Responses of visual cells in cat superior colliculus to relative pattern movement.

Are there visual cells in the cat superior colliculus, selectively sensitive to relative pattern movement? Based on extracellular recordings from paralyzed pretrigeminal preparations, a sample of 76 collicular units could be divided into two main types according to relative movement sensitivity: those that responded optimally and selectively to one specific relative velocity between a small disk and a full-field grating; and those that discharged maximally whenever the grating shifted relative to a disk moving at one specific "absolute" speed, regardless of the precise relative velocity between the two. It was hypothesized that the latter group, in conjunction with extraretinal "calibration" cues, may be part of a neural mechanism encoding spatial depth in terms of motion parallax.