Prosocial apathy for helping others when effort is required

Abstract

Prosocial acts - those that are costly to ourselves but benefit others - are a central component of human co-existence1-3. While the financial and moral costs of prosocial behaviours are well understood4-6, everyday prosocial acts do not typically come at such costs. Instead, they require effort. Here, using computational modelling of an effort-based task we show that people are prosocially apathetic. They are less willing to choose to initiate highly effortful acts that benefit others compared to benefitting themselves. Moreover, even when choosing to initiate effortful prosocial acts, people show superficiality, exerting less force into actions that benefit others than themselves. These findings replicated, were present when the other was anonymous or not, and when choices were made to earn rewards or avoid losses. Importantly, the least prosocially motivated people had higher subclinical levels of psychopathy and social apathy. Thus, although people sometimes 'help out', they are less motivated to benefit others and sometimes 'superficially prosocial', which may characterise everyday prosociality and its disruption in social disorders.

Figure 1. Prosocial Motivation Measure (PMM) for Self vs. Other

a. In Study 1 participants were assigned to two different roles in the experiment completely anonymously. They made choices between a fixed low effort, low reward option (shown on left) or a variable higher effort (30%, 40%, 50%, 60%, 70% maximum voluntary contraction, MVC) but higher reward option (2-10 credits). Once a choice was made the chosen force was exerted on a handheld dynamometer in the participant’s dominant hand (Exert effort). Only if the required level was reached for 1s out of a 3s window would the offered reward be obtained, otherwise 0 credits would be delivered. On half the trials, the credits on offer were for themselves (Self: shown in red). On the other half of trials, credits were for the other participant (Other: blue). b. In Study 2 participants met face-to-face with a confederate (whom they believed to be another participant taking part in the same study). Participants took part in two sessions in counterbalanced order. In one session, they made choices to win money for the other person and themselves; in another session, they made choices to avoid losing money for the other person and themselves.

Figure 2. Prosocial apathy when deciding to exert effort to reward others.

A. Proportion of higher effort/higher reward option chosen over baseline option (lower reward, lower effort) plotted against effort (top panel) and reward levels (bottom panels) in Study 1 (n=48). Effort levels 1-5 correspond to 30, 40, 50, 60 and 70% of a participant’s maximum voluntary contraction (MVC). Reward levels 1-5 correspond to 2, 4, 6, 8 and 10 credits. Participants chose the high effort/higher reward option more frequently for self (red bars) than other (blue bars), with this difference increasing with effort level. They were also less reward sensitive for other people than themselves. Error bars show S.E.M. B. In Study 2 (n=45), people again chose the higher effort/higher reward option more frequently for self than other, with this effect increasing with effort level (top panel). Participants were also less reward sensitive for others compared to self (bottom panel). Error bars show S.E.M. C. When making choices to avoid losing for self or other in Study 2, participants chose the higher effort/lower loss option more frequently for self than other (top) and were less loss sensitive for self than other. Error bars show S.E.M.

Figure 3. Model comparison robustly shows across two studies that a model with separate discount parameters for self and other best explains behaviour.

A. Model comparison results from Study 1 with x-axis depicting model number and y-axis the sum of Bayesian information Criterion (BIC) Score. Models with parabolic, linear and hyperbolic discounting functions with either single (models 1-6) or separate discount (K) parameters (models 7-10) for self and other and/or single (red and green) or separate noise (β) parameters (yellow and blue) for self and other. A parabolic model with separate parameters for self and other discounting but a single noise parameter best explained participant’s behavior and in the majority of subjects (model 7 in all studies), which was determined by having the lowest summed BIC score in combination with explaining behaviour in the majority of participants. Pie chart shows the proportion of participants the winning model explains behaviour in (green) compared to the same model with separate noise parameters (blue). Asterisks show the two models with lowest BIC scores. B Model comparison results from Study 2-win replicated the winning model from Study 1. Asterisks show the two models with lowest BIC scores. C Model comparison results from Study 2-lose also replicated the winning model from Study 1 and Study 2-win. Asterisks show the two models with lowest BIC scores. D Mathematical formula for the winning parabolic model. The graph shows discount parameters for the median K scores for self and other at reward level 4 for illustrative purposes.

Figure 4. Reduced force when exerting effort to help others.

Even when choosing the experimental option for other, participants applied less grip force than when applying force to reward themselves. A. Force exerted as the total area under the curve during the ‘effort period’ on each trial (top panel). Participants applied less grip force when rewarding the other person compared to self at the higher levels of effort. In a linear regression, Agent, Reward, Effort and the Agent x Effort interaction were all significant predictors of force exerted (all p<.001). Asterisks show significant beta weight (p<.001). Error bars show S.E.M. B. Reduced force when rewarding others was replicated in Study 2 (top). As in Study 1, Agent, Reward, Effort and Agent x Effort interaction were significant predictors of force exerted (all p<.001). Asterisks show significant beta weight (p<.001). Error bars show S.E.M. C. Participants also applied less force when avoiding losses for others compared to self (top). Agent, Reward and Effort were again all significant predictors of force exerted (all p<.001). Asterisks show significant beta weight. Error bars show S.E.M. (p<.001). Together, these results show that people are superficially prosocial, even after choosing to exert effort participants apply less grip force to reward other people than themselves.