Abstract: Regret is defined as an emotion that occurs when the outcome is worse than it could have been had one made a different choice. Its neural mechanism has become a hot area in social cognitive neuroscience. The orbitofrontal cortex (OFC) has been shown to play a key role in the experience of regret. Researchers propose that regret feeling and activities of OFC could be influenced by the degree of responsibility in choice process. Prior behavioral research indicated that responsibility influenced the regret feeling about incorrect decisions. But to date the relationship between responsibility magnitude and regret intensity has not been explored. Whether an individual would experience gradually augmented regret as a result of the increment of responsibility is the core question in our study. The regret level is the main independent factor in the current experiment. According to the theory of responsibility diffusion, the levels of responsibility could be manipulated by the number of people responsible for an incorrect choice on a trial-by-trial basis. The more individuals shall make a decision, the weaker sense of responsibility they would feel. We also intend to explore this effect by investigating temporal process, brain activities, as well as self-reported ratings. Thus, the special components of ERPs, including fERN and P300, were measured in a gamble task fulfilled by three participants together. We hypothesized that the amplitudes of fERN would be significantly different between the condition of taking responsibility alone and the other conditions.
An ERP experiment with 15 undergraduates (8 males, 7 females) was conducted to test the hypothesis. The result of each trial was displayed by an equilateral triangle. There were three levels of responsibility: 1(the participant made the wrong choice by his/her own); 1/2 (the participant and one of the collaborators made the wrong choice); 1/3 (all three participants made the wrong choice). Participants’ event-related potential data during the presence of the triangle, as well as the self-reported ratings were analyzed off-line. The fERN was calculated as the voltage difference between the most negative peak between 250-350ms and the preceding positive peak after the appearance of feedback, while the amplitude of P300 was calculated as the mean amplitude between 350-550ms. The brain electrical source analysis technique (BESA) was also conducted to estimate the dipole sources of fERN and P300.
Participants’ sense of responsibility was much higher in the wrong choice alone condition than the other conditions and the evaluation of counterfactual thinking became higher as the magnitude of responsibility went larger. The amplitude of fERN was distinctively larger in the wrong choice alone condition than the other conditions, indicating that binary evaluation was also influenced by top-down modulations. On the other hand, the P300 amplitude was inversely related to the number of people responsible for an incorrect choice. This is consistent with the notion that their personal accountability for the consequences of a choice influences the allocation of attentional and cognitive resources to the task. Sourcing analysis showed that fERN might be generated from brain regions near the anterior cingulate cortex (ACC) and right sub-gyral, while the P300 was related to the precuneus and medial frontal gyrus.
The result confirms our hypothesis that increment of responsibility leads to stronger regret feelings. It also implies that error-related processing could be modulated by responsibility magnitude, which in turn regulates feelings of post-decision regret.

Key words: regret, responsibility, outcome evaluation, the ERPs