After-Effects Of Effort Expenditure: Cognitive Versus Physical Effort

Effort not only prospectively subtracts the reward value before effort expenditure but also retrospectively adds the reward value after effort expenditure.However,work on the mechanisms underlying increased reward value following effort expenditure has yielded heterogeneous results.Based on previous studies,an important factor of elucidating these inconsistent results is the type of effort expenditure,which has not been examined whether the after-effect of effort expenditure depends on its type.The present study is the first one to investigate the behavioral and neural dynamics underlying the effort-reward relationship in different type of effort throughout four experiments.In Experiments 1,2and 3,one hundred and fifty-seven participants completed an effortful task,which effort was manipulated in trials level,in high-effort trials and low-effort trials,and then played a gambling game to earn monetary rewards.Their risk-taking tendency during the gambling game was measured as index of reward evaluation.The effortful task was either cognitive or physical;the decision context in the gambling game was either risky where the outcome probability was known or ambiguous where the outcome probability was unknown.Behavioral results suggested that investing effort facilitates subsequent risktaking behaviors at a short,trial-to-trial scale,which is robust.Importantly,the risk-taking after-effect occurs across cognitive and physical effort in a domain-general way,but occurs across risky and ambiguous decision context in a domain-specific way.The risktaking after-effect of effort exertion is restricted to trials with a greater probability cost in the risky decision context rather than in the ambiguous decision context,regardless of effort type.Thirty-two participants were recruited for Experiment 4 and the procedure of Experiment 4 was similar to previous three experiments.Given that the risk-taking behaviors adopted in previous three experiments involved more executive functions,we adopted an easier choice task to exclude the influence of cognitive control in Experiment4.Participants performed varied levels of physically or cognitively effortful task and then selected one of two doors to earn monetary rewards while their EEG was recorded.EEG results revealed that: effort discounts reward value as reflected by the reward positivity and the subsequent P3 for high-versus low-effort trials.The P3 was differentially sensitive to the discounting after-effects of cognitive and physical effort expenditure,whereas the reward positivity was comparably sensitive to the discounting after-effects of cognitive and physical effort expenditure.These results suggested that the existence of a cost-invariant mechanism between effort types(cognitive effort versus physical effort),but the cost-invariant mechanism is separate between the behavioral and neural measures.This study was the first one to examine the effort-reward relationship under different type of effort in trials level.These findings provide new insights into understanding the inconsistent results of the after-effects of effort expenditure,and further extend the P3 as an index of distinct psychological and neural mechanisms between cognitive effort and physical effort,and are helpful to have a better understanding of the neural mechanism of effort-based motivational diseases,such as depression,anhedonia,schizophrenia.