A neural model of smooth pursuit control and motion perception by corticalarea MST

Smooth pursuit eye movements (SPEMs:) are eye rotations that are used to ma intain fixation on a moving target. Such rotations complicate the interpret ation of the retinal image, because they nullify the retinal motion of the target, while generating retinal motion of stationary objects in the backgr ound. This poses a problem for the oculomotor system, which must track the stabilized target image while suppressing the optokinetic reflex. which wou ld move the eye in the direction of the retinal background motion (opposite to the direction in which the target is moving). Similarly the perceptual system must estimate the actual direction and speed of moving objects in sp ite of the confounding effects of the eye rotation. This paper proposes a n eural model to account fur the ability of primates to accomplish these task s. The model simulates the neurophysiological properties of cell types foun d in the superior temporal sulcus of the macaque monkey, specifically the m edial superior temporal (MST) region. These cells process signals related t o target motion, background motion, and receive an efference copy of eye ve locity during pursuit movements. The model focuses on the interactions betw een cells in the ventral and dorsal subdivisions of MST, which are hypothes ized to process target velocity and background motion, respectively. The mo del explains how these signals can be combined to esl,lain behavioral data about pursuit maintenance and perceptual data From human studies, including the Aubert-Fleischl phenomenon and the Filehne Illusion. thereby clarifyin g the functional significance of neurophysiological data about these MST ce ll properties. It is suggested that the connectivity used in the model may represent a general strategy used by the brain in analyzing the visual worl d.