Binocular cells

V1 is the first area in which input from both eyes is combined. Most cells, specifically in layers 4B, 2, and 3 illustrate binocular responses, in which they can be driven by either eye.

This is an essential condition for stereopsis. Most of the binocular cells show a preference for one eye, a phenomenon termed to as ocular dominance. The cells which have similar ocular dominance (example, those that are driven preferentially by the ipsilateral eye) take place ocular dominance columns which are located in long stripes about 500 µm across. The columns representing ipsilateral and contra-lateral input alternate regularly over the cortex and, when visualized at the level of layer 4C, appear like the pattern of stripes on a zebra.

The receptive fields of binocularly driven cells look like those of simple or complex cells, lie in corresponding locations in the two retinas, have alike orientation properties and have similar arrangements of excitatory and inhibitory areas. The same input from both eyes into arrays of binocular cells is required for perception of a fused image. To that extent, inputs into these cells are not equal they measure retinal disparity and therefore are the V1 cells responsible for stereopsis.