Complex Cells in the Cat Striate Cortex Have Multiple Disparity Detectors in the Three-Dimensional Binocular Receptive Fields

Abstract

Along the visual pathway, neurons generally become more specialized for signaling a limited subset of stimulus attributes and become more invariant to changes in the stimulus position within the receptive fields (RFs). One of the likely mechanisms underlying such invariance appears to be pooling of detectors located at different positions. Does such spatial pooling occur for disparity-selective neurons in primary visual cortex? To examine whether the three-dimensional (3D) binocular RFs are constructed by pooling detectors for binocular disparity, we investigated binocular interactions in the 3D space for neurons in the cat striate cortex. Approximately one-third of complex cells showed the spatial pooling of disparity detectors to a significant degree, whereas the majority of simple cells did not. The degree of spatial pooling of disparity detectors along the preferred orientation axis was generally larger than that along the axis orthogonal to the orientation axis. We then reconstructed 3D binocular RFs in their complete form and examined their structures. Disparity tuning curves were compared across positions along the orientation axis in the RFs. A small population of cells appeared to show a gradual shift of the preferred disparity along this axis, indicating that they can potentially signal inclination in the 3D space. However, the majority of cells exhibited a position-invariant disparity tuning. Finally, disparity tuning curves were examined for all oblique angles in addition to horizontal and vertical. Tunings were broadest along the orientation axis as the disparity energy model predicts.

Integration of Multiple Spatial Frequency Channels in Disparity-Sensitive Neurons in the Primary Visual Cortex

“…Each cell was classified into simple or complex based on standard criteria (F1/F0 ratio; Skottun et al, 1991). The balance of responses between the two eyes was quantified using the binocularity index (Sasaki et al, 2010).…”

Disparity processing in primary visual cortex

“…That so many components of this are visible in the responses of V1 neurons indicates a surprisingly sophisticated computation, and yet one that can be performed by the extended BEM. The contribution of multiple subunits can be demonstrated in a more direct way if a sufficiently large stimulus set is used to probe disparity signals in different sub-regions of the RF [6]. Figure 4 illustrates the principle used.…”

“…If the cell is composed of two subunits, each of which is a BEM, and they have different Y locations, then the cell's response will be an inseparable function of Y L , Y R , elongated along the diagonal (figure 4e). The extent of this elongation can be used to estimate a minimum number of subunits, and a substantial number of neurons recorded by Sasaki et al [6] needed more than three subunits to account for the responses. This combination of spatially offset subunits was illustrated by modification (b) in figure 1.…”

“…if some dot patterns led to changes in the contrast gain), the set of LN filters recovered by STC may be quite different from the true RF subunits of a given cell. The method of Sasaki et al [6] requires far fewer assumptionsthe fact that dots that are separated but still within the RF show no binocular interaction clearly indicates that the RF is divided into subunits with distinct binocular RFs, regardless of any nonlinearities within those sub-regions. The disadvantage of this method is that it gives a much less complete picture of the properties of those subunits.…”

“…Having multiple subunits helps Figure 4. Binocular interactions across different locations in the RF can be used to identify different subunits (after Sasaki et al [6]). (a,b) An RF (for simplicity, it is identical in right and left eyes), with a row of random dots superimposed.…”