Abstract

The primate fovea enjoys excellent color and spatial vision despite being dominated by a cell that is specialized for neither color nor acuity. Ingling and Martinez [Vision Res. 23, 1495 (1983)] have shown that the r-g X-cell adds surround and center responses for color and subtracts surround from center responses for acuity. In effect, hue signals are encoded by a low pass filter and luminance (form) signals are encoded by a bandpass filter. The multiplexed signals are transmitted to the cortex, where a demultiplexing operation must take place. Two demultiplexing algorithms—Russell (nonlinear) filtering and cancellation-have been discussed in the literature. We introduce a linear filtering algorithm that can be implemented easily in neural systems. Computational experiments with Mondrians show that linear filtering with a thresholding operation produces results identical to Russell filtering. We discuss psychophysical and electrophysiological evidence for each method and show how cortical color opponent, double opponent, and achromatic (high resolution) cells can arise from the simple opponent r-g type I cells. The multiplexing/demultiplexing operation allows the visual system to substitute computation for bandwidth in the r-g X-cell channel.

© 1989 Optical Society of America