Electrophysiological evidence of multitasking impairment of attentional deployment reflects target-specific processing, not distractor inhibition.

We studied the interaction between the control mechanisms subserving spatial attention and central attention using the psychological refractory period (PRP) paradigm. Two stimuli, a pure tone (T(1)) and a circular visual array (T(2)), including a salient target and a salient distractor, were presented at varying stimulus onset asynchronies, each requiring a speeded response. Target-specific and distractor-specific lateralized event-related potentials were isolated by placing one of them at a lateral position and the other on the vertical midline. As SOA was decreased, a progressive reduction and postponement of a T(2)-locked N2pc component was observed with a lateral target and a central distractor. No lateralized potentials were associated with a lateral distractor and a central target. The sustained posterior contralateral negativity (SPCN) was observed independently of SOA modulation, only with a lateral target. We also observed an earlier positive deflection, the Ppc (positivity posterior contralateral), that was contralateral to both lateral targets and distractors, whose amplitude and latency were not affected by SOA variations. We conclude that central processing interferes specifically with target processing reflected by the N2pc and SPCN. We propose that the Ppc reflects an initial, bottom-up response to the presence of a salient stimulus, whereas the N2pc and SPCN reflect the controlled deployment of spatial attention to targets and maintenance of target information in visual short-term memory, respectively.