The Neural Representation of Stereoscopic Depth Contrast

Stereoscopic vision provides examples of contrast phenomena broadly analogous to those seen with brightness. Several authors have suggested that lateral inhibition between disparity-tuned neurons might underlie these phenomena. This type of lateral inhibition would differ from the more familiar kind which occurs with retinal ganglion cells, where an inhibitory surround has essentially a linear subtractive effect. Lateral inhibition by disparity-tuned units would introduce the nonlinearity of the tuning curve. I argue here that the evidence nonetheless suggests that a linear subtractive mechanism operates in the stereo realm—in fact, that there is a stereo equivalent of the classical centre-surround. This seems at first sight implausible, partly because of the occurrence of the nonlinearity mentioned above, but also because disparity is only provided at certain locations in the retinal field, namely those where appropriate features are matched. I show that both objections can be easily overcome, the first because Laplacian-like centre–surrounds can be constructed from disparity-tuned cells, the second because interpolation can fill in between features, and can provide precisely the quantitative dependence upon disparities of neighbouring features which matches the experimental data.