The representation of three-dimensional visual space in the cat's striate cortex

1. Binocularly driven single units were recorded in the cat's striate cortex. For each neurone the two monocular receptive fields were stimulated simultaneously in order to assess the optimal positioning of the image in both eyes to give the best binocular response.2. The electrode was driven perpendicular to the surface of the brain to explore cortical columns, all the cells of which are known to have the same preferred target orientation.3. All orientation columns were found to fit into one of two classes according to their binocular organization.4. In a constant depth column the receptive fields of binocular neurones cover a small retinal area and they are laid out in almost identical arrays in the two eyes. Consequently, the horizontal disparity is practically the same for all the units. The depth column as a whole is viewing a thin sheet of visual space, a few degrees wide, floating at some distance from the cat. There may be about 0.6 degrees disparity difference between neighbouring depth columns.5. In a constant direction column the binocular units' fields are all super-imposed on the retina contralateral to the hemisphere containing the column. In the ipsilateral eye they are more scattered horizontally. Therefore the horizontal disparity varies enormously from cell to cell and the column as a whole is viewing a cylinder of visual space directed towards the contralateral eye. Neighbouring direction columns may vary by about 4 degrees in their oculocentric visual direction.6. This columnar arrangement is probably important for space perception in the cat. Activity in only one depth and one direction column would specify the orientation and the three-dimensional locus of an object in space.7. The two types of column may be involved in the control of disjunctive and conjugate eye movements.