A MODEL OF THE COMBINATION OF OPTIC FLOW AND EXTRARETINAL EYE-MOVEMENT SIGNALS IN PRIMATE EXTRASTRIATE VISUAL-CORTEX - NEURAL MODEL OF SELF-MOTION FROM OPTIC FLOW AND EXTRARETINAL CUES

The determination of the direction of heading from optic flow is a com plicated task. To solve it the visual system complements the optic flo w by non-visual information about the occurrence of eye movements. Psy chophysical studies have shown that the need for this combination depe nds on the structure the visual scene. In a depth-rich visual environm ent motion parallax can be exploited to differentiate self-translation from eye rotation. In the absence of motion parallax, i.e. in the cas e of movement towards a frontoparallel plane, extraretinal signals are necessary for correct heading perception (Warren and Hannon, 1990). L appe and Rauschecker (1993b) have proposed a model of visual heading d etection that reproduces many of the psychophysical findings in the ab sence of extraretinal input and links them to properties of single neu rons in the primate visual cortex. The present work proposes a neural network model that integrates extraretinal signals into this network. The model is compared with psychophysical and neurophysiological data rom experiments in human and non-human primates. The combined visual/e xtraretinal model reproduces human behavior in the case of movement to wards a frontoparallel plane. Single model neurons exhibit several sim ilarities to neurons from the medial superior temporal (MST) area of t he macaque monkey. Similar to MST cells (Erickson and Thier, 1991) the y differentiate between self-induced visual motion that results from e ye movements in a stationary environment, and real motion in the envir onment. The model predicts that this differentiation can also be achie ved visually, i.e. without extraretinal input. Other simulations follo wed experiments by Bradley et al. (1996), in which flow fields were pr esented that simulated observer translation towards a frontoparallel p lane plus an eye rotation. Similar to MST cells, model neurons shift t heir preference for the focus of expansion along the direction of the eye movement when extraretinal input is not available. They respond to the retinal location of the focus of expansion which is shifted by th e eye movement. In the presence of extraretinal input the preference f or the focus of expansion is largely invariant to eye movements and ti ed to the location of the focus of expansion with regard to the visual scene. The model proposes that extraretinal compensation for eye move ments need not be perfect in single neurons to achieve accurate headin g detection. It thereby shows that the incomplete compensation found i n most MST neurons is sufficient to explain the psychophysical data. ( C) 1998 Elsevier Science Ltd. All rights reserved.