To study the electrophysiological correlates of conscious vision, we recorded event-related potentials (ERPs) in a patient with partial unilateral visual extinction as a result of right-hemisphere damage. When, following bilateral presentations, contralesional stimuli were not perceived, there was an absence of the early attention-sensitive P1 (80-120 msec) and N1 (140-180 msec) components of the ERP response. In contrast, following unilateral presentations, or in those bilateral presentations in which contralesional stimuli were perceived (about 60%), these ERP components were present. These results provide novel evidence that extinction involves the stage of early focusing of attention and that the P1 and N1 components of visual ERPs are reliable physiological correlates of conscious vision.

Motion information tends to be segregated from color and form information in the visual system, both perceptually and neuroanatomically, and it is therefore possible that different mechanisms of attention are used to select targets defined by these different feature types during visual search. To test this hypothesis, we recorded the N2pc component of the event-related potential waveform during visual search tasks with color, orientation, and motion targets. The N2pc component has previously been shown to reflect a specific attentional mechanism that is present for color and form targets, and we sought to determine whether this component would also be present for motion targets. The N2pc component was indeed observed for motion targets as well as color and orientation targets, consistent with the use of a common attentional mechanism across feature types. In addition, we found that motion singletons (i.e., individual items that moved in the opposite direction from the other items in the army) elicited an N2pc component even when they were task-irrelevant, indicating that motion discontinuities may produce an automatic orienting of attention.