Topographic Signatures of Global Object Perception in Human Visual Cortex

Abstract

Our visual system readily groups dynamic fragmented input into global objects. How the brain represents such perceptual grouping remains however unclear. To address this question, we recorded brain responses using functional magnetic resonance imaging whilst observers perceived a dynamic bistable stimulus that could either be perceived globally (i.e., as a grouped and coherently moving shape) or locally (i.e., as ungrouped and incoherently moving elements). We further estimated population receptive fields and used these to back-project the brain activity during stimulus perception into visual space via a searchlight procedure. Global perception resulted in non-topographic suppression of responses in lower visual cortex accompanied by wide-spread enhancement in higher object-sensitive cortex. However, follow-up experiments indicated that higher object-sensitive cortex is suppressed if global perception lacks shape grouping, and that grouping-related suppression can be diffusely confined to stimulated sites once stimulus size is reduced. These results speak against a rigid between-area response amplitude code acting as a generic grouping mechanism and point to a within-area response amplitude code mediating the perception of figure and ground.