On the control of visual spatial attention: evidence from human electrophysiology

We used electrophysiological methods to track the deployment of visual spatial attention while observers were engaged in concurrent central attentional processing, using a variant of the attentional blink paradigm. Two visual targets (T-1, T-2) were presented at a stimulus onset asynchrony of either 200 ms or 800 ms. T-1 was a white digit among white letters presented on a dark background using rapid serial visual presentation at fixation. T-2 was another digit that was presented to the left or right of fixation simultaneously with a distractor digit in the opposite visual field, each followed by a pattern mask. In each T-2 display, one digit was red and one was green. Half of the subjects reported the red digit and ignored the green one, whereas the other half reported the green digit and ignored the red one. T-1 and T-2 were reported in one block of trials, and only T-2 in another block (order counterbalanced across subjects). Accuracy of report of T-2 was lower at short SOA than at long SOA when both T-1 and T-2 were reported, but was similar across SOA when only T-2 was reported. The electrophysiological results focused on the N2pc component, which was used as an index of the locus of spatial attention. N2pc was reduced in amplitude when subjects reported T-1, and particularly so at the short SOA. The results suggest that attention to T-1 interfered with the deployment of visual spatial attention to T-2.