The influence of contextual stimuli on the orientation selectivity of cells in primary visual cortex of the cat.

Perception of a visual attribute, such as orientation, is strongly dependent on the context within which a feature is presented, such as that seen in the tilt illusion. The possibility that the neurophysiological basis for this phenomenon may be manifest at the level of cells in striate cortex is suggested by anatomical and physiological observations of orientation dependent long range horizontal connections which relate disparate points in the visual field. This study explores the dependency of the functional properties of single cells on visual context. We observed several influences of the visual field area surrounding cells' receptive field on the properties of the receptive field center: inhibition or facilitation dependent on the orientation of the surround, shifts in orientation preference and changes in the bandwidth of orientation tuning. To relate these changes to perceptual changes in orientation we modeled a neuronal ensemble encoding orientation. Our results show that the filter characteristics of striate cortical cells are not necessarily fixed, but can be dynamic, changing according to context.