The P4pc: an electrophysiological marker of attentional disengagement?

The processing of successive targets requires that attention be engaged and disengaged. Whereas attentional engagement can be studied by means of the N2pc component of the event-related potential (ERP), no ERP component has been linked to attentional disengagement. Here, we report the finding of such a component using an RSVP paradigm with multiple, successive targets and with a spatial-cuing paradigm. In both experiments, disengagement of attention was necessary to attend to subsequent targets. A distinct waveform following the N2pc, which we call the P4pc (Positivity 400 ms post-target posterior contralateral), was found. The P4pc was found when a lateralized cue indicated that attention would be needed for the processing of a target at either the same or a different location as the cue, but not when only the cue was to be responded to, indicating that the need to disengage attention is a prerequisite for the P4pc to occur. We expect the P4pc to provide a valuable addition to the set of electrophysiological measures used to study the dynamics and mechanisms of visual attention and visual search.