Different time courses of event-related potentials in spatial search for emotionally loaded faces

Recognition of facial expressions has been investigated extensively over the last decade. However, the mechanism of advanced processing of emotional expressions as compared to neutral ones remains unclear. In our study, a face-in-the-crowd task with crowds of neutral and emotionally biased faces was performed by 18 normal subjects. Event-related potentials were recorded and analyzed in response to (a) different facial expressions (positive/negative) and (b) different detection difficulties induced by varying the number of faces. Results show that: (1) When responding to negative faces the late component (500-800 ms post-stimulus) showed a positive shift compared to positive faces; (2) A unique negative component for negative faces was observed at approximately 400 ms in fronto-central regions. In addition, no significant influence of emotional expressions on the early cognitive stages was observed. The N2 amplitude decreased only with increasing detection difficulty in processing the all neutral faces. Our results suggest that the time courses of ERPs to negative and positive faces differ, which implies different search strategies for negative and positive faces.