Figure 1.

Two hypotheses of how cortical simple cells encode binocular disparity. (a) Position encoding. Binocular disparity is encoded through a difference in position between left and right eye RFs that have the same profile (7–9). In the figure, the two eyes are fixating at a point, F, in depth. Receptive field positions in the two eyes of a simple cell can be at retinal correspondence (C) or can be shifted to either side of the corresponding point as shown for the right eye, creating RF position disparity between the two eyes. Depending on the amount of RF position disparity, various binocular disparities can be encoded. (b) Phase encoding. Alternatively, binocular disparity may be encoded through a difference in RF profile (phase) between the two eyes (RF phase disparity) without RF position disparity (10–17). The left eye RF and three variations of the right eye RF shown in the figure are at retinal correspondence (i.e., there is no RF position disparity) in the sense that the envelope of each RF (– ⋅ –) is centered at C. However, RF phases for the two eyes can be different, creating RF phase disparity through which binocular disparity can be encoded.