Claim tree

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

Among the computational models fitted to momentary happiness data, the Responsibility Redux model achieved the best (lowest) AIC in both studies (Study 1 AIC –1499; Study 2 AIC –1195).

methodological table1

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

The anterior insula is the neural substrate of the guilt effect, increasing its BOLD response when participants are responsible for low outcomes affecting their partner.

hypothesis —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

If the anterior insula tracks guilt, then insula BOLD should be higher in the Social than the Partner condition and show a significant Social-by-low-outcome interaction.

prediction —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The authors suggest this left STS region tracks a partner's unexpected outcomes less when they do not follow from the participant's decisions.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The behavioural guilt effect (larger happiness decrease after low partner outcomes following participant rather than partner choices) is compatible with 'simple guilt'.

interpretation —

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

In both studies, participants felt worse after low lottery outcomes for the partner when those outcomes followed their own choice rather than the partner's, which the authors interpret as interpersonal guilt.

synthesis —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

If connectivity between the guilt- and responsibility-related outcome-phase regions (left insula, left STS) and prefrontal cortex depends on whether participants decide for themselves alone or also for their partner and on the type of choice, then a seed-to-voxel psychophysiological-interaction analysis seeded in these regions should reveal prefrontal clusters showing a significant Condition-by-Choice interaction.

prediction —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Connectivity between the left anterior insula and the right inferior frontal gyrus varied with choice and condition, suggesting this prefrontal region is sensitive to guilt-related information during social choices.

interpretation —

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

Decisions in the Social compared with the Solo condition engaged three clusters — the precuneus (d = 0.79), left temporo-parietal junction (d = 0.59), and medial prefrontal cortex (d = 0.54).

empirical fig4b

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

The difference in response between low and high lottery outcomes was greater in the Social than the Partner condition in left insula (0.44***), right insula (0.19***), and right middle temporal cortex (0.67***).

empirical app1table10

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

Dot products between individual neural guilt responses and the Yu et al. (2020) guilt-related brain signature (GRBS) were overall positive (mean = 5.22, median = 6.97, sign test p = 0.017, Cliff's Delta = 0.4), providing convergent validity with a previously published neural guilt signature.

control —

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During the outcome phase, responses to low lottery outcomes were higher in the Social than the Partner condition in both left and right insula (InsulaL 0.41***, InsulaR 0.18***) and lower in the right middle temporal cortex (–0.12**).

empirical app1table9

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

During receipt of lottery versus safe outcomes (across all conditions), clusters were more active in the bilateral anterior insula, dmPFC, right STS, bilateral ventral striatum, right dorsolateral prefrontal cortex, and bilateral inferior parietal lobe.

empirical fig4d

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

On each trial participants chose between a safe and a risky monetary option under three conditions: choosing for oneself (Solo), for oneself and the partner (Social), and having the partner choose for both (Partner).

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

The findings rest on two samples of healthy adults — Study 1 (behaviour only, N = 40) and Study 2 (fMRI, N = 44); all BOLD/fMRI results derive from Study 2, while the behavioural results come from both studies.

scope —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between guilt- and responsibility-related outcome-phase regions and prefrontal cortex changes depending on whether participants decide for themselves alone or also for their partner, and on the type of choice (Safe or Risky).

hypothesis —

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

Functional connectivity between the left anterior insula (seed) and a cluster in the right inferior frontal gyrus varied with condition and choice, being highest when participants made Risky choices for themselves and Safe choices for both players (pFWE = 0.020, T = 4.34, d = 0.80, 115 voxels, peak MNI [46 16 22]).

empirical fig5

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

The guilt effect occurred whether the participant received the high lottery outcome (Study 1: t(39) = –3.58, p < 0.001, d = 0.56; Study 2: t(43) = –2.68, p = 0.01, d = 0.4) or the low outcome (Study 1: t(39) = –3.39, p = 0.002, d = 0.54; Study 2: t(43) = –3.58, p < 0.001, d = 0.54).

control —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

To hold the partner's behaviour constant across participants, the partner's decisions were simulated by an algorithm that always selected the option with the highest expected value.

methodological —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

Individual GRBS dot-product values did not correlate with the behavioural guilt responses (Spearman's Rho = –0.058, p = 0.725), indicating the neural signature does not track individual differences in behavioural guilt sensitivity.

control —

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

The insula ROIs responded more to low lottery outcomes for the partner in the Social than the Partner condition — even after subtracting responses to high outcomes — mirroring the behavioural guilt effect.

empirical fig4e

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

A left IFG cluster showed the opposite pattern of connectivity with the left STS seed — highest for Safe-self / Risky-both-players choices — but did not survive correction for multiple comparisons (p uncorrected = 0.001, T = 4.44, 35 voxels, peak MNI [–48 14 6]).

empirical fig5s1

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

The left superior temporal sulcus cluster responded to model-based regressors coding participant reward prediction resulting from participant and partner choices across both sessions of the experiment.

empirical fig4i

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

A likelihood ratio test showed the Responsibility model fitted the happiness data better than all other models, including the Responsibility Redux model (Study 1: all LR ≥ 47.36, p < 0.0001; Study 2: all LR ≥ 77.83, p < 0.0001).

empirical table1

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The linear mixed model containing all three two-way interaction terms (Model 5, Equation 10) explained the happiness data significantly better than simpler models without interactions (p < 2e−5) and no worse than the model with all interactions (p > 0.5), warranting reporting the crucial partnerHigh:participantDecided (guilt) interaction from it.

methodological app1table2

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

The lower happiness when the participant is the decision-maker may reflect responsibility aversion — a cost of the 'weight of the responsibility'.

interpretation —

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

A mass-univariate voxel-wise analysis found a small left anterior insula cluster (peak T = 3.95, d = 0.59, 22 voxels) responding more to low partner outcomes following participant than partner choices, which survived small-volume family-wise-error correction (p = 0.024).

empirical fig4f

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

In mixed-effects regressions on choices, the Social condition significantly increased choice of the risky option in Study 1 but not in Study 2.

empirical app1table1

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

A model-based GLM (GLM2) entered the best-fitting computational (Responsibility) model's variables — certain rewards (CR), expected value (EV), participant RPE (sRPE), and partner RPE from participant choices (social_pRPE) and from partner choices (partner_pRPE) — as regressors to locate brain regions reflecting them.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Model selection among the happiness models used likelihood-ratio tests comparing the Responsibility model pairwise against each other model, supplementing the AIC, BIC, R² and adjusted R² values.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

Momentary happiness was modelled with five computational models (Basic, Inequality, Guilt-envy, Responsibility, and Responsibility Redux) sharing separate, exponentially decaying terms for certain rewards, expected value, and reward prediction errors.

methodological —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

If a neural substrate tracks the participant's responsibility for the partner's outcomes, then within regions sensitive to the outcomes of risky choices, BOLD should respond more strongly to the partner's reward prediction errors resulting from the participant's own choices than from the partner's choices.

prediction —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

A neural substrate tracks the participant's responsibility for the partner's outcomes: within regions sensitive to choice outcomes, the partner's reward prediction errors are represented more strongly when they arise from the participant's own choice than from the partner's choice.

hypothesis —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

There was no significant interaction between the difference in expected values and experimental conditions in either study (p > 0.52).

control —

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

One cluster in the left STS responded more to partner reward prediction errors resulting from participant rather than partner choices (pFWE = 0.022, T = 4.70, d = 0.53, 100 voxels, peak MNI [−52 –32 0]).

empirical fig4h

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

Only the precuneus and TPJ showed positive Risky–Safe differences in both the Social>Solo and Social>Partner comparisons, being most active when participants chose the lottery in the Social condition.

empirical fig4c

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

A parameter-recovery procedure on synthetic data generated from each participant's estimated parameters showed the happiness-model parameters could be reliably recovered, verifying their stability.

methodological fig3s1

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant happiness was lower when the participant was the decision-maker (Social + Solo vs. Partner), independent of outcome (Study 1: t(3600) = –3.92, p < 0.0001, β = –0.14; Study 2: t(2870) = –6.07, p < 0.0001, β = –0.24).

empirical —

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the partner received in the current trial.

empirical fig3b,fig3f

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participant momentary happiness varied with the rewards the participant received in the current trial.

empirical fig3a,fig3e

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants chose the risky option (lottery) more often in the Solo than the Social condition in Study 1 (t(4796) = 2.54, p = 0.011, β = 0.164) but not in Study 2 (t(3829) = 0.23, p = 0.82, β = 0.015).

empirical fig2a,fig2d

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' own reward prediction errors (sRPE) influenced happiness more than the partner's reward prediction errors (social_pRPE and partner_pRPE) (Study 1: all Z > 6.0, p < 0.001; Study 2: all Z > 3.7, p < 0.003).

empirical —

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants' probability of choosing the risky option (lottery) increased with the difference between the expected value of the lottery and the value of the safe option (Study 1: t(4796) = 9.26, p < 3.1e–20, β = 0.074; Study 2: t(3829) = 10.62, p < 5.3e–26, β = 0.093).

control fig2a,fig2d

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants showed very similar risk preferences whether deciding only for themselves (Solo) or for themselves and their partner (Social), with only a tendency toward higher risk aversion in the Social condition in Study 1.

synthesis —

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

Participants were slightly more risk averse (higher ρ) in the Social than the Solo condition in Study 1 (t(39) = 2.27, p = 0.03, d = 0.36, BF10 = 1.69) but not in Study 2 (t(43) = 1.40, p = 0.17, d = 0.21, BF10 = 0.41).

empirical fig2c,fig2f

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

The partner's reward prediction errors resulting from the participants' own choices (social_pRPE) had weights greater than 0 (Responsibility model: Study 1: Z = 2.85, p = 0.004; Study 2: Z = 3.26, p = 0.001), contributing to explaining participants' momentary happiness.

empirical —

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

A pre-task icebreaker succeeded in establishing a positive attitude toward the partner: participants rated their partners highly (all above 8 on a 1–10 scale) on sympathy, cooperativity, honesty, openness, and sociability in both studies.

control app1table11

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior functional connectivity work has shown network differences between social and self-only choices, midbrain–anterior cingulate interactions during guilt compensation, and links between insula connectivity and responsibility aversion.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Prior literature documents an association between the anterior insula and guilt.

literature-context —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

Responsibility for choices did not influence happiness following positive (high) lottery outcomes for the partner (both studies, all |t| < 1.3, p > 0.2, BF10 < 0.2).

control —

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

The Responsibility model yielded higher R² values than all other models (Study 1: all t > 3.6, p < 0.007; Study 2: all t > 2.9, p < 0.034), except the Guilt-envy model in Study 1 (t = 2.19, p = 0.17).

empirical table1

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for outcomes generates guilt, then participant happiness should decrease more after low lottery outcomes for the partner when the participant rather than the partner chose the lottery.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

If responsibility for the partner's outcomes influences the participant's momentary happiness, then a computational model that includes the partner's reward prediction errors arising from the participant's own choices (social_pRPE) should explain the happiness data better than models omitting them, and social_pRPE weights should be reliably greater than zero.

prediction —

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

The Responsibility Redux model — incorporating expected, previous and current rewards, reward prediction errors for both participant and partner, and decision-maker — predicted the variations in participants' momentary happiness well.

empirical fig3c,fig3g

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

Responsibility for a social choice that yields a low outcome for a partner produces interpersonal guilt, experienced by the decision-maker as a larger decrease in momentary happiness than when the partner made the same choice.

hypothesis —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

The risk-aversion parameter ρ did not differ between gain and loss trials (Study 1: t(17) = 0.21, p = 0.84, d = 0.05; Study 2: t(15) = –0.61, p = 0.55, d = 0.15), justifying pooling across gain and loss trials.

control —

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Risk premiums did not differ between Solo and Social conditions in either study (Study 1: t(39) = 1.53, p = 0.134, d = 0.24, BF10 = 0.49; Study 2: t(43) = –0.21, p = 0.84, d = –0.03, BF10 = 0.17).

control fig2b,fig2e

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Rutledge and colleagues established that changes in momentary happiness during a probabilistic reward task are explained by recent reward expectations and the prediction errors arising from them.

literature-context —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

Study 2 reproduced the Study 1 design inside the fMRI scanner with identical parameters except for longer inter-stimulus intervals (3–11 s) and partners who were experimenters positioned outside the scanner.

scope —

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

When the partner received the low lottery outcome, participant happiness was lower when the participant rather than the partner had chosen the lottery — a significant partner-outcome × decision-maker interaction (Study 1: t(1180) = 3.52, p = 0.0004, β = 0.37; Study 2: t(937) = 2.85, p = 0.0045, β = 0.33) — operationalizing interpersonal guilt.

empirical fig3d,fig3h

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness cost observed in the Social condition is general agency aversion — the unpleasantness of being the decision-maker as such — and is not contingent on responsibility for a negative outcome befalling the partner.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The happiness decrease following negative partner outcomes under participant choice is driven by the participant's own lottery outcome rather than by the partner's, and so reflects self-directed disappointment rather than interpersonal guilt.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The imaging pipeline and condition contrasts do not recover established effects, so differences reported between Social and Partner conditions cannot be attributed to the experimental manipulation.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

The model-based fMRI approach does not recover known neural signals, so parametric modulators derived from the computational model — including the partner reward prediction error regressors — cannot be trusted.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

Participants did not engage with the lottery task in a value-sensitive way — choices were inattentive or random — so the behavioural measures carry no information about preference or affect.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

The happiness and choice differences between Social and Partner conditions reflect a social-context-driven shift in risk attitude — participants become more or less risk averse when choosing on another person's behalf — rather than responsibility-contingent interpersonal guilt.

hypothesis —

Bilateral ventral striatum shows greater BOLD response when participants choose the risky (lottery) rather than safe option, irrespective of Social or Solo condition (left cluster: Cohen's d=0.72; right cluster: d=0.85), replicating established striatal responses to risky decision-making.

control fig4a

The bilateral ventral striatum was more active when participants chose the risky rather than the safe option (Cohen's d = 0.72 left, 0.85 right), irrespective of Social or Solo condition, replicating previous findings.

control fig4a ~0.58

Bilateral ventral striatum activation increases with the computational model's expected certain rewards and expected values of chosen lotteries (left: pFWE=0.002, T=5.63, d=0.75, Z=5.41, 110 voxels, MNI [−14 8 −8]; right: pFWE=0.005, T=5.46, d=0.70, Z=5.26, 80 voxels, MNI [10 10 −4]), validating the model-based fMRI approach as a manipulation check before the STS analysis.

control fig4g

As a manipulation check, bilateral ventral striatum activation increased with expected certain rewards and the expected values of chosen lotteries, explained by a model-based regressor coding participant rewards (left: pFWE = 0.002, T = 5.63, d = 0.75; right: pFWE = 0.005, T = 5.46, d = 0.70).

control fig4g ~0.56