Task Relevance Modulates Early Threat and Prediction Signals in Face Processing: An Event-Related Potential Study

Threat and prediction signals are proposed to influence perceptual processing automatically. Here, we examine how the pre-allocation of spatial attention and the task relevance of the stimulus modulate early neural responses to likely and unlikely facial expressions. Thirty participants viewed pairs of bilaterally presented stimuli consisting of either faces (one emotional, one neutral) or Gabor patches (one tilted, one vertical). Electroencephalography was recorded, and early ERPs associated with visual processing (P1 and N170) were analyzed. Participants were explicitly informed of the probabilities with which each facial expression would appear, and then engaged in one of three tasks: judging the emotion of facial expressions, the orientation of Gabor patches, or the location of missing pixels at a central fixation cross. We observed that event probabilities modulated P1 amplitudes and that facial threat modulated N170 amplitudes. Critically, these modulations were reliable only when facial expressions were task relevant. They were absent when faces were task irrelevant, including when spatial attention remained pre-allocated to the face locations. Together, these findings suggest that early neural responses to threat and prediction signals depend on task-relevant engagement with the stimulus rather than on the pre-allocation of spatial attention alone, constraining accounts that characterize these effects as automatic.