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 (T₁, T₂) were presented at a stimulus onset asynchrony of either 200 ms or 800 ms. T₁ was a white digit among white letters presented on a dark background using rapid serial visual presentation at fixation. T₂ 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 T₂ 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. T₁ and T₂ were reported in one block of trials, and only T₂ in another block (order counterbalanced across subjects). Accuracy of report of T₂ was lower at short SOA than at long SOA when both T₁ and T₂ were reported, but was similar across SOA when only T₂ 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 T₁, and particularly so at the short SOA. The results suggest that attention to T₁ interfered with the deployment of visual spatial attention to T₂.