Abstract: Closeness of outcome refers to the degree of distance between real behavioral outcomes and desired outcomes. Previous studies revealed that closeness of outcome was one of the main factors that induce counterfactual thinking about the outcome, and played an important role in inducing post-decisional emotions (e.g., regret, rejoicing). Although some recent researches have explored how closeness of outcome affects negative outcome evaluation (e.g., losing money) in gambles, there is no evidence that whether it modulates positive outcome evaluation (e.g., gaining money). By simultaneously recording event-related potentials (ERPs) data from participants engaged in a simple like-slot-machine gambling task, the present study aimed to further investigate that whether and how closeness of outcome modulated feedback outcome evaluation when gaining money.
Fourteen healthy undergraduates (7 males and 7 females, age 19-24, M=21.6 years) were recruited to take part to this study. The participants in the experiment were all right-hand, had normal or corrected-to-normal vision and had no neurological or psychological disorders. Each participant signed a consent form prior to the experiments and was paid after the experiment. The study was approved by the local academic committee.
In this experimental task, closeness of feedback outcome was manipulated through depending on the distance between feedback outcome and desired outcome in the screen in the gambling task. Thus, three conditions were included in analyzed results: near-gain, general-gain, and full-gain. The EEG was recorded from 64 scalp channels using electrodes mounted in an elastic cap. Feedback-related ERPs, including feedback-related negativity (FRN) and P300, were calculated for a 1200 ms epoch including a 200 ms pre-feedback baseline. The amplitude of FRN and P300 were peek-to-peak measured separately in the 200~300 ms and 300~500 ms time windows after the appearance of feedback.
Behavioral results suggested that emotional response of the participants was obviously modulated by the closeness of outcome. Specially, participants tended to use the emotional word “rejoicing” to describe their feelings when near-gains, and tended to use the word “elation” to describe their feelings when full-gains. In addition, the closeness of feedback outcome also modulated the reaction time of participants in the next trial following it, in which, participants’ reaction time was evidently longer when near-gains, compared with the one when full-gains and general-gains. ERP results indicated that the FRN and P300 were sensitive to the closeness of outcome, with near-gains eliciting larger amplitudes of the FRN and larger amplitudes and longer latencies of the P300, compared with full-gains and general-gains. These results revealed that positive outcome evaluation is also modulated obviously by closeness of outcome.

Key words: closeness of outcome, outcome evaluation, FRN, P300, ERP