The subregion correspondence model of binocular simple cells.

We explore the hypothesis that binocular simple cells in cat areas 17 and 18 show subregion correspondence, defined as follows: within the region of overlap of the two eye's receptive fields, their ON subregions lie in corresponding locations, as do their OFF subregions. This hypothesis is motivated by a developmental model (Erwin and Miller, 1998) that suggested that simple cells could develop binocularly matched preferred orientations and spatial frequencies by developing subregion correspondence. Binocular organization of simple cell receptive fields is commonly characterized by two quantities: interocular position shift, the distance in visual space between the center positions of the two eye's receptive fields; and interocular phase shift, the difference in the spatial phases of those receptive fields, each measured relative to its center position. The subregion correspondence hypothesis implies that interocular position and phase shifts are linearly related. We compare this hypothesis with the null hypothesis, assumed by most previous models of binocular organization, that the two types of shift are uncorrelated. We demonstrate that the subregion correspondence and null hypotheses are equally consistent with previous measurements of binocular response properties of individual simple cells in the cat and other species and with measurements of the distribution of interocular phase shifts versus preferred orientations or versus interocular position shifts. However, the observed tendency of binocular simple cells in the cat to have "tuned excitatory" disparity tuning curves with preferred disparities tightly clustered around zero (Fischer and Krüger, 1979; Ferster, 1981; LeVay and Voigt, 1988) follows naturally from the subregion correspondence hypothesis but is inconsistent with the null hypothesis. We describe tests that could more conclusively differentiate between the hypotheses. The most straightforward test requires simultaneous determination of the receptive fields of groups of three or more binocular simple cells.