Dynamic properties of visual cortex
The response properties of cells in primary visual cortex indicate a role in contour integration and surface segmentation. These responses are as dependent on the global characteristics of contours and surfaces extending beyond their receptive fields as they are on the attributes of features within their receptive fields. Features in the receptive field surround can influence the selectivity of cells for features within the receptive field, and can alter even the dimensions of the receptive field itself. These contextual influences show the strongest attentional modulation in primary visual cortex. Contextual influences are also modified by perceptual learning, and the influence of learning is manifest in a task-dependent fashion. The contextual influences, and their modulation by experience, attention and behavioral task are likely to involve an interaction between long range connections within primary visual cortex and feedback connections from higher order cortical areas. Cells in V1 are capable of encoding more complex stimuli than previously believed, and this specificity is derived from the systematic relationship between short and long range cortical connections and cortical functional architecture. The emerging picture is that the properties of cells, even at early stages in visual processing, are dynamic, changing according to visual context, experience, attention and behavioral context.