Geometry of orientation and ocular dominance columns in monkey striate cortex.

In addition to showing that ocular dominance is organized in slabs and that orientation preferences are organized in linear sequences likely to reflect slabs, Hubel and Wiesel (1974a) discussed the intriguing possibility that slabs of orientation might intersect slabs of ocular dominance at some consistent angle. Advances in optical imaging now make it possible to test this possibility directly. When maps of orientation are analyzed quantitatively, they appear to arise from a combination of at least two competing themes: one where orientation preferences change linearly along straight axes, remaining constant along perpendicular axes and forming iso-orientation slabs along the way, and one where orientation preferences change continuously along circular axes, remaining constant along radial axes and forming singularities at the centers of the spaces enclosed. When orientation patterns are compared with ocular dominance patterns from the same cortical regions, quantitative measures reveal (1) that singularities tend to lie at the centers of ocular dominance columns, (2) that linear zones (arising where orientation preferences change along straight axes) tend to lie at the edges of ocular dominance columns, and (3) that the short iso-orientation bands within each linear zone tend to intersect the borders of ocular dominance slabs at angles of approximately 90 degrees.