Event-related brain potential in responses to social messages via human faces

In two experiments participants were presented a sequence of facial photographs to examine effects of pleasantness of facial expressions, namely, pleasant and unpleasant, and task relevance on P300 component of event-related brain potentials in the 3-stimulus version of the oddball task. Exp. 1 showed that, although the amplitudes of P300 were the largest in response to task-relevant target stimuli and moderate in response to task-irrelevant nontargets, the Pleasantness of stimuli did not affect the amplitudes of P300 when the stimuli were task-relevant or irrelevant. Data in Exp. 2 suggested that the emotional significance rather than physical characteristics of stimuli might be responsible for generation of P300 by task-irrelevant nontargets.