Anisotropy of the Orientation Selectivity in the Visual Cortex Area 18 of Cats Reared Under Normal and Altered Visual Experience

Abstract

The “oblique effect” refers to the reduced visual performance for stimuli presented at oblique orientations compared to those at cardinal orientations. In the cortex, neurons that respond to specific orientations are organized into orientation columns. This raises the question: Are the orientation signals in the iso-orientation columns associated with cardinal orientations the same as those in the iso-orientation columns associated with oblique orientations, and is this signal influenced by experience? To explore this, iso-orientation columns in visual area 18 were examined using optical imaging techniques. Kittens were raised under either standard or modified conditions, including total darkness or rhythmic light stimulation through one or both eyes, which could potentially disrupt the orientation tuning of visual neurons. A signal profile around the pinwheel center was calculated to assess the distribution of the orientation signal within the hypercolumn. This profile exhibits a sinusoidal pattern with identifiable minima and maxima. To emphasize that these amplitude variations are localized within a specific circle rather than throughout the entire optical map, we used the terms “local minima” and “local maxima.” The number of local maxima in areas corresponding to oblique orientations was similar to those in regions associated with vertical orientations. The highest number of local maxima was found in horizontal iso-orientation columns, indicating a “horizontal bias.” This finding may be related to the postnatal development of sensory–sensory and sensory–motor integrations involving the visual system. We propose that the data presented should be incorporated into mathematical models of visual cortex activity, as well as vision itself.