A negative deflection in the event-related potential is enhanced following error- and loss-related feedback in decision-making and simple gambling tasks. Researchers have assumed that the perceptual properties of the feedback stimuli are unimportant in explaining these effects. This assumption was tested in the present study through a flanker gambling task, in which the perceptual properties of the feedback were manipulated. Consistent with previous studies, loss elicited a larger feedback-related negativity (FRN) than gain feedback. However, this FRN reward effect was modulated by the perceptual properties of the feedback stimuli. When gain and loss feedback were perceptually similar to each other, the enhancement of the FRN following the loss feedback was smaller compared to when the gain and loss feedback were different from each other. In addition, incongruent feedback elicited a larger FRN than congruent feedback; this FRN congruency effect was larger following gain than loss feedback. These results suggested that perceptual properties of the feedback stimuli play a role in the elicitation of the FRN.