Abstract: Some researches have investigated the relativity in outcome evaluation, but it is unclear about what the reference point is and its brain mechanism when the participants evaluate the relative value and relative magnitude. Enlightened by “Prospect theory” of reference point effect, we speculate that the feedback-related ERPs may represent reference point effect. In order to explore the hypothesis, this research distinguished the relative information based on a reference point and the absolute information based on zero by using Bet-feedback money gamble task.
Event-related brain potentials (ERPs) were measured when 12 healthy college students did Bet-feedback money gamble task. We mainly analyzed ERPs elicited by the five feedbacks outcome following two bet conditions.
The results showed a similar tendency in FRN and P300. The amplitude of the FRN elicited by the first feedback was largest, and the amplitude of the FRN elicited by the fifth feedback was smallest, and the amplitudes of the FRN elicited by the second, third and fourth feedbacks were intermediate between that of the first and that of fifth feedback. The difference between the amplitude of the P300 elicited by the first feedback and that by the fifth feedback was not significant, while the amplitudes of the P300 elicited by the other three feedbacks did not show significant difference. The amplitudes of the P300 elicited by the first feedback and by the fifth feedback are larger than those of the other three feedbacks. In summary, the results showed that the amplitudes of both FRN and P300 elicited by the second, third and fourth feedbacks, in which the financial gap between bet and feedback is small in relative magnitude, are not significantly different; the amplitudes elicited by the three feedbacks and those elicited by the first and fifth feedbacks, in which the financial gap between bet and feedback is large in relative magnitude, show significant difference.
These results revealed that feedback-related ERPs reflect the processing of relative information based on a reference point, but the reference point was not the bet but the space where bet was. By reference to the space where bet was, the amplitude of FRN elicited by loss (i.e. the first feedback) was larger than that of gain (i.e. the fifth feedback) and the amplitude of FRN elicited by even (i.e. the other three feedbacks) was in the middle. According to the space of bet, the amplitude of P300 elicited by the larger feedback in relative magnitude is larger than that of the smaller feedback in relative magnitude, while the amplitude of P300 elicited by the equal feedback in the relative magnitude is not different significantly.
Therefore, the feedback-related ERPs reflected the processing of the relative information based on the space of bet, showing effect of reference point, rather than the processing of the absolute information referring to point of zero

Key words: FRN, P300, reference point effect