A negative voltage deflection in the event-related brain potential is enhanced following error- and loss-related feedback in simple gambling and decision-making tasks. Investigators have assumed that the perceptual properties of the feedback stimuli are unimportant in explaining these effects of feedback. This assumption has been tested in the present study through a series of seven ERP experiments using gambling tasks. In the experiments, participants were asked to make a choice between several gambles and then received feedback indicating whether they won or lost during the trial. The perceptual properties of the feedback were manipulated. Consistent with previous research, neutral and loss feedback elicited a larger FRN than gain feedback, and there was no FRN difference between neutral and loss feedback. However, this FRN reward effect was modulated by the perceptual similarity among the feedback stimuli. When gain and neutral/loss feedback were similar to each other, the enhancement of the FRN following the neutral/loss-related feedback was smaller compared to when the gain and neutral/loss feedback were different from each other. In addition, perceptually salient feedback tended to produce a larger FRN effect than less perceptually salient feedback, and when the reward information was indicated by conjoined features, the FRN reward effect was diminished. Furthermore, the presence of perceptual interference in the feedback stimuli enhanced the FRN-like negativity. Letter strings comprising different letters elicited a larger FRN than those comprising identical letters, even when different letters were mapped to the same reward. This FRN congruency effect could not simply be explained by semantic interference. No FRN congruency effect was found when the reward information was unknown to the participants, suggesting that the perceptual mismatch that induced the FRN congruency effect has to be task-relevant. A perceptual mismatch model is proposed to explain all the experimental results.
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