Abstract
Vision is an active process. The receptive field properties of cortical neurons are subject to learning and to top-down influences of attention, expectation and perceptual task. Even at early cortical stages of visual processing neurons are subject to contextual influences that play a role in intermediate level vision, contour integration and surface segmentation, which enables them to integrate information over large parts of the visual field. These influences are not fixed but are subject to experience, enabling neurons to encode learned information. Even in the adult the visual cortex there is considerable plasticity, where cortical circuits undergo exuberant changes in axonal arbors following manipulation of sensory experience. The integrative properties of cortical neurons, the contextual influences that confer selectivity to complex stimuli, are mediated in part by a plexus of long range horizontal connections that enable neurons to integrate information over an area of visual cortex representing large parts of the visual field. These connections are the substrate for an association field, a set of interactions playing a role in contour integration and saliency. The association field is not fixed. Rather, neurons can select components of this field to express difference functional properties. As a consequence neurons can be thought of as adaptive processors, changing their function according to behavioral context, and their responses reflect the demands of the perceptual task being performed. The top-down signal facilitates our ability to segment the visual scene despite its complex arrangement of objects and backgrounds. It plays a role in encoding and recall of learned information. The resulting feedforward signals carried by neurons convey different meanings according to the behavioral context. We propose that these dynamic properties are mediated by an interaction between reentrant signals to the cortex and intrinsic cortical connections, changing effective connectivity within the cortical network. The evolving view of the nature of the receptive field includes contextual influences which change in the long term as a result of perceptual learning and in the short term as a result of a changing behavioral context.
Meeting abstract presented at VSS 2013