Functional organization of neurons in cat striate cortex: variations in preferred orientation and orientation selectivity with receptive-field type, ocular dominance, and location in visual-field map

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Abstract
The preferred stimulus orientation, orientation tuning range, ocular dominance, receptive-field location and receptive-field type were assessed for neurons in area 17 of cat visual cortex. The neurons were divided into 3 cell types: simple I, simple II and complex. Anisotropies in the frequency of occurrence of cells preferring stimuli with particular orientations were found in area 17. These anisotropies were most pronounced for simple I and complex cells. Orientation anisotropies were also found relative to receptive-field size and ocular dominance. Cells with small receptive fields had a more prominent bias for horizontal and vertical stimuli than cells with large receptive fields. Overall, monocular cells of all receptive-field types exhibited no biases for any particular orientation, although monocular simple II cells preferred vertical stimuli. Binocular simple II cells preferred horizontal stimuli, while binocular complex cells preferred horizontal and vertical stimuli. To take into account naturally occurring anisotropies in the visual field, retina and cerebral cortex, the visual field was divided into 2 Cartesian and 2 polar coordinate schemes. As a result of these divisions, although all orientations were represented at all locations, many neurons with receptive fields near the vertical meridian preferred horizontal stimuli, while neurons with receptive fields near the horizontal meridian tended to prefer vertical stimuli. Neurons with receptive fields at the center of visual space, near the intersection of the 2 major meridians, preferred horizontal and vertical stimuli. Neurons outside these regions showed less anisotropy in orientation preference. The anisotropy for horizontal and vertical stimulus preferences in central vision extended to an eccentricity of at least 12.degree.. A systematic relationship between preferred orientation and angular location of a receptive field from the center of visual space was found. Simple I cells tended to prefer orientations organized along radii or concentric circles centered on the middle of visual space, while complex cells had preferred orientations predominantly along concentric circles. Orientation selectivity varied with receptive-field type, being narrowest for simple I cells and broadest for complex cells. Orientation selectivity changed little with increasing eccentricity for any cell type. At all locations, complex cells had the broadest orientation tuning range preferred orientations are highly organized within the map of the visual field in area 17. This organization is discussed in terms of perception and the dynamic visual flow field as described by Gibson.