Mandatory Processing of Irrelevant Fearful Face Features in Visual Search

Faces expressing fear may attract attention in an automatic bottom-up fashion. Here we address this issue with magneto-encephalographic (MEG) recordings in subjects performing a demanding visual search combined with the presentation of irrelevant neutral or fearful faces. The impact of the faces 'emotional expression on attentional selection was assessed by analyzing the N2pc component-a modulation of the event-related magnetic field response known to reflect attentional focusing in visual search. We observed that lateralized fearful faces elicited an N2pc approximately between 240 and 400 msec in ventral extrastriate cortex that was independent of the N2pc reflecting target selection in visual search. Despite their clear influence on neural processing, fearful faces did not significantly influence behavioral performance. To clarify this discrepancy, we further performed an MEG experiment in which the demands of the search task were reduced. Under those conditions, lateralized fearful faces elicited an N2pc response that was again independent of the N2pc response to the search target. Behavioral performance was, however, influenced in a significant manner, suggesting that for behavioral effects to appear, sufficient attentional resources need to be left unoccupied by the search task-a notion put forward by the perceptual load theory. Our observations are taken to indicate that irrelevant fearful faces influence attentional processing in extrastriate visual cortex in an automatic fashion and independent of other task-relevant attentional operations. However, this may not necessarily be echoed at the behavioral level as long as task-relevant selection operations exhaust attentional resources.