Event-related potentials to overlapping shapes: Effects of saliency and interference

Abstract

Visual perception is often challenged by various difficulties that act concomitantly and whose respective impacts may therefore be hard to distinguish. We used event-related potentials to dissociate the impact of target saliency, generated by occlusion, from that of interference produced by incongruent nontargets. In one block, the target (a square) partially occluded another square tilted by 45º. This nontarget square interfered only to a small extent with target perception. In another block, the target was the occluded stimulus, and interference from the nontarget was substantial. Blocks including two kinds of overlapping shapes (a cross and a square) were added to control for the interference effect. Block comparisons revealed that occlusion modulated an occipital N250 and reaction times. In contrast, interference modulated a parietal N380 but not reaction times. Attention, Perception, & Psychophysics 2010, 72 (6) a cross, and a square over a square tilted by 45º. Three additional stimuli were created by tilting each of these stimuli by 45º. The stimuli with interference were the stimuli with two squares. They will be referred to as the same-shape stimuli. The noninterfering stimuli were the stimuli with a cross. They will be designated as the different-shape stimuli. The stimuli were inlaid in a black annulus used to create a condition in Brodeur, Lepore, Bacon, and Debruille (2009). It was preserved here to make the results of the present study comparable to those of the previous one.

The beneficial influence of inattention on visual interference in schizophrenia.

“…Interference effects on ERPs occur later, generally starting at around 250 ms after the stimulus onset. The interference ERP characteristically manifests as a negative potential shift within a broad time window, lasting 200 to 400 ms, over central or posterior electrodes (Brodeur, Lepore, Bacon, Renoult, & Debruille, 2010).…”