Int. J. Man-Machine Studies (1975) 7, 547-569 Eye Movements and Visual Perception: A "Two Visual System" Model* RICHARD L. DIDDAY Information Sciences, University of California, Santa Cruz, California 95064, U.S.A. AND MICHAEL A. ARBIB Department of Computer and Information Science, and Center for Systems Neuroscience, University of Massachusetts at Amherst, Amherst, Massachusetts 01002, U.S.A. (Received 13 February 1975) Eye movement is one of the few externally measurable activities of visual per- ception, and provides a checkpoint for models of perceptual processes. Here the model of Arbib & Didday (1971) is compared with that of Noton & Stark (1970, 1971a, b), and is found to predict the same behavior but without requiring explicit storage of eye movement commands. Introduction Eye movement is one of the few externally measurable activities of visual perception. There have been a number of studies of eye movements in the last 150 years; Yarbus (1967) lists about a 100 relevant references. There is a trend toward using saccadic eye movements (the rapid, co-ordinated rotation of the eyes from or/e "point" of fixation to the next) to infer the functioning of brain processes which are not directly measurable. For example, some workers [Tichomirov & Poznyanskaya (1967) and Newell & Simon (1972)] use measurements of such movements to uncover chess players' board analy- sis techniques. Noton & Stark (1970, 1971a, b) have used such measurements to test a hypothesis about a memory scheme and its relationship to patterns of eye movements. This paper presents a model of the role of eye movements which builds on neurophysiological investigations of the "two visual systems" of Ingle, Schneider, Trevarthen & Held (1967); and which yields an alternative interpretation of Noton & Stark's results. *An earlier version of this paper was presented at the Conference on Biologically Moti- vated Automata Theory held at the MITRE Corporation, MacLean, Va., 19-21 June, 1974. 547