Reward association alters brain responses to emotional stimuli: ERP evidence.

We investigated the effects of reward learning on the processing of emotional faces using event-related potentials (ERPs). A simple choice game was used to imbue angry and happy faces with a high or low probability of reward. ERPs were recorded in a subsequent test phase in which participants performed a visual search task to discriminate the emotion of a face singleton as being angry or happy without any reward. Results revealed a significant interaction between reward-history and emotion for the N1 and P2 components, in which the difference between the mean amplitudes for angry and happy faces was smaller in the high-reward association condition than in the low-reward association condition. This reward-modulation effect indicates that reward association reduced the initial visual awareness and hence attentional allocation to angry faces. Moreover, we found a positive relationship between the personal trait of reward sensitivity and the reward-modulation effect for the late-latency response-selection related slow positive wave (SPW) component and the behavioral response accuracy, suggesting that participants with higher reward sensitivity may employ more cognitive resources to evaluate the reward history during the late decision stage of emotional processing. Our study contributes to a better understanding of how reward-association history affects both the perceptual and executive levels of emotional face processing.