Neuronal circuits capable of generating visual cortex simple-cell stimulus preferences.

Abstract

The range of simple-cell stimulus preferences to be found at each point in the striate cortex can be accounted for in terms of a model of retinocortical and intracortical circuits. It is assumed that each hypercolumn represents a conformal logarithmic mapping of its aggregate field, or hyperfield. Retinal-unit-field centres within the same aggregate field are assumed to be nonoverlapping, and overlap between retinal centres is attributed to a marked overlap between, adjacent aggregate fields. Unit-field centres are assumed to be arranged regularly along aggregate-field radii, with diameters which increase linearly with ecentricity. Retinal-unit-field centres project retinotopically to overlapping clusters consisting of nine cortical pillars, and each pillar receives from a corresponding cluster of nine retinal-unit=field centres. Under this mapping, aggregate-field radii project to orientation columns, and concentric semicircules project to spatial-frequency columns. Inhibitory basket-cell axons project at right angles to the orientation columns, in parallel with the spatial-frequency columns, to produce a range of preferences and tuning curves for orientation, symmetry, directionality, and length. The same circuits also offer explanations for adaption phenomena such as tilt aftereffects, and suggest ways in which attentional mechanisms might operate.