Figure 1. A neuronal population which explicitly encodes horizontal, but not vertical, disparity.

The shaded region represents the space of two-dimensional disparity on the retina [14]. The purple disks represent the preferred 2D disparity of an idealized population of disparity sensors. Although these sensors form a one-dimensional population, all tuned to zero vertical disparity, they can nevertheless encode two-dimensional stimulus disparity, e.g. the stimulus disparity represented by the green dot, which has both a horizontal and a vertical component. (Cf figure 1 of Serrano-Pedraza & Read [16].)