Stereoscopic Depth Channels for Position and for Motion

Summary

In this chapter we summarize psychophysical and single-neuron evidence that information as to movement in depth and information as to position in depth are processed in different psychophysical channels and possibly by different neural mechanisms. One item of evidence is that inspecting a target oscillating in depth reduces visual sensitivity to depth motion, but only for a restricted range of trajectories close to the adapting trajectory. This suggests that there are several binocularly-driven neural filters, each of which is preferentially sensitive to a different direction of motion in depth. Further evidence is the existence of areas of the visual field blind to motion in depth but where positional (static) depth perception is normal. Supporting evidence obtained by single-neuron recording in cat cortex is the existence of two classes of neuron that emphasize information as to the direction of motion in depth rather independently of position: one class prefers trajectories passing between the eyes while the other class prefers trajectories that miss the head. A third class of neuron is well known. This class is sensitive to position in depth and is best driven by binocularly-viewed sideways motion.