Electrophysiological correlates of perceptual reversals for three different types of bistable images

Abstract

Bistable stimuli, i.e. stable visual images that can be perceived in two mutually exclusive ways, offer unique tools for dissociating perceptual from stimulus-driven changes in visual processing. Recently, event-related potentials (ERPs) have been employed to investigate the time-course of these endogenous changes in visual perception. For example, using a variant of the Necker cube, Kornmeier & Bach (2004, 2005) identified a ‘reversal negativity’ ERP component, i.e. a broad increase in negative potential extending from 200–400msec post-stimulus, for trials in which observers reported perceptual reversals. To further investigate the reversal negativity, as well as possible earlier influences on bistability, the current study employed three different types of bistable stimuli: a modified Rubin's face/vase, a modified Schröder's staircase, and a novel stimulus, Lemmo's cheetahs. Using a 128-channel system, 21 observers viewed flashing bistable stimuli, time-locked to the EEG recording, and indicated reversals by a button-press. Results show clear reversal negativities for all three bistable stimuli. In addition, an effect of early visual spatial attention on figure reversals was implicated by an analysis of the early occipital P1 & N1 ERP components. The P1 & N1 were enhanced for trials in which the observer reported perceptual reversals as compared to trials in which no reversals were reported for the face/vase and staircase, but not for the cheetahs. Taken together these results support a model of bistable perception in which changes in early spatial attention (indicated by P1 & N1 enhancement) modulate reversals (indicated by the reversal negativity).