Abstract: Prosocial behavior often requires people to invest their own effort so that someone else can benefit. Yet theories and empirical work have largely emphasized the value of others’ outcomes, whereas the cost of the effort one personally incurs has received far less attention. The few studies that directly address prosocial effort have concentrated on effort-based reward decisions made before any effort is exerted, such as whether people are willing to work for rewards delivered to themselves or to others. This decision-stage focus leaves a critical dynamic question unanswered: once effort has actually been performed, does it continue to devalue the outcome obtained for others, or retrospectively enhance it, as it does for self-benefiting effort?
To address this question, we propose a two-stage model of how prosocial effort shapes reward processing. The model builds on the effort paradox observed in nonsocial contexts, in which effort exerts opposite effects at different processing stages. Before action, higher effort prospectively discounts reward value because it is encoded as a cost, whereas after action the same effort can retrospectively enhance reward value through effort justification or contrast effects. Extending this framework to the social domain, we argue that the effort-reward relationship depends on the beneficiary. When people work for themselves, reward processing should follow the classic effort paradox, showing prospective devaluation before effort exertion and retrospective enhancement after effort exertion. When people work for an anonymous other, however, effort may be encoded mainly as a personal cost weighed against someone else’s gain. Prosocial effort would then produce a double-devaluation pattern, reducing subjective reward value both before and after the effort is exerted. This prediction offers a new account of prosocial apathy: people may fail to help not because they do not care about others, but because the effort required to help persistently suppresses the perceived value of the outcome.
The proposed research will test this model along two integrated lines of investigation. Study 1 examines the cognitive and neural mechanisms by comparing reward processing when participants exert cognitive effort to earn rewards for themselves versus for anonymous strangers. Experiment 1 will use behavioral tasks to measure decision preferences before effort and affective evaluations after reward feedback, together with computational modeling of effort discounting. Experiments 2a and 2b will extend this design with EEG and fMRI. EEG will resolve the temporal dynamics of reward processing at the cue and feedback stages, and fMRI will localize the cortical and subcortical reward-related regions. Together, these experiments will reveal whether prosocial effort yields neural evidence of double devaluation, and whether this pattern diverges from the effort paradox observed in self-benefiting effort. Study 2 further tests whether the proposed mechanism is domain-general or domain-specific across effort types and benefit domains. Experiment 3 contrasts cognitive with physical effort, using matched task structures to examine whether prosocial effort produces comparable neural dynamics across cognitively and physically demanding tasks. Experiment 4 compares reward gain with loss avoidance, asking whether exerting effort to prevent another person’s loss shifts prosocial valuation toward the self-benefiting pattern. Experiment 5 compares reward gain with harm avoidance by adding a pain avoidance context, thereby testing whether a morally salient benefit to another person attenuates or reverses the double-devaluation pattern.
The innovation of this work lies in reconceptualizing prosocial behavior as a continuous effort-reward integration process rather than a static cost-benefit choice. It introduces effort cost and its temporal dynamics into the study of prosocial behavior, distinguishes two competing hypotheses, and links behavioral decisions, subjective experience, electrophysiological dynamics, and neural valuation within a single framework. By clarifying how effort reshapes the value of benefits to others before and after its exertion, the research will address a key gap in current theories of prosocial behavior and provide a new perspective on how self-incurred costs and others' benefits are balanced, and on how such behavior can be promoted.

Key words: prosocial behavior, cognitive effort, reward, effort paradox