Abstract
Our visual system groups image elements of objects and segregates them from other objects and the background. I will discuss the neuronal mechanisms for these grouping operations, proposing that there are two processes for perceptual grouping. The first is ‘base grouping’, which is a process that relies on neurons tuned to feature conjunctions and occurs in parallel across the visual scene. If there are no neurons tuned to the required feature conjunctions, a second process, called ‘incremental grouping’, comes into play.
Incremental grouping is a time-consuming and capacity-limited process, which relies on the gradual spread of enhanced neuronal activity across the distributed representation of an object in the visual cortex, during a delayed phase of the neuronal responses. Incremental grouping can occur for only one object at any one time. The spread of enhanced activity corresponds to the spread of object-based attention at the psychological level of description. Hence, we found that the binding problem is solved by labelling the representation of image elements in the visual cortex with enhanced activity and we did not obtain any evidence for a role of neuronal synchronization.
Inhibition of the late-phase activity in primary visual cortex completely blocked figure-ground perception, demonstrating a causal link between enhanced neuronal activity and perceptual organization. These neuronal mechanisms for perceptual grouping account for many of the perceptual demonstrations by the Gestalt psychologists.