Occlusion-related cue used for analysis of motion in the primate visual cortex.

Although cells in ventral part of the medial superior temporal area (MST) do not respond to movements of a wide textured field, many of them start to respond when a stationary object is placed in front of the moving field. The effective direction in this stimulus configuration is opposite to the preferred direction of individual cells for movement of an object. Here, we examined what stimulus cues were detected by the cells in response to movements of a background pattern behind an object. The responses disappeared when the border of the object was blurred. Because blurring the border degraded an occlusion-related cue, i.e., appearance and disappearance of components of the background at the border, we conclude that the occlusion-related cue is essential for the responses.