Attending to a location in three-dimensional space modulates early ERPs.

It has been reported that attending to a particular location can modulate incoming sensory signals, as reflected by the stimulus-evoked P1 and N1 components of the visual event-related potential (ERPs) in a two-dimensional (2D) display [Attention, Space, and Action: Studies in Cognitive Neuroscience, Oxford University Press, New York, 1999, p. 31]. In contrast, in this study we examined the effect of attention in 3D space using a stereoscopic display. Stimuli were presented randomly, one at a time, in an orthogonal combination of two depths (near, far) and two 2D locations (left, right) relative to the fixation point. The task was to attend selectively to one of these four positions and to respond to a target stimulus defined by shape in the attended 3D location. The effect of 2D location selection on the P1 amplitude was greater for stimuli in the near than the far depth plane, and the amplitude of N1 increased in response to stimuli in the attended combination of 2D location and depth. These results suggest that the effect of early spatial selection on the visual ERP is not simply based on retinotopic organization of the visual field, but also on intermediate stages that construct a 3D spatial representation of the external world.