An investigation of the relationship between eye and retinal inlage movement in the perception of movementl ARIENMACK2 NEW SCHOOL FOR SOCIAL RESEARCH The question investigated was whether correlative phenomenon of no perceived perception of object mation and or not eye movements accompanied by movement despite the occurrence of retinal correlatively if eye movements are not abnormal retinal image movements, displacement to maintain that retinal image matched by retinal image displacements, movements t1uJt are either or both at a movement is either a sufficient or mavement will be perceived. Thus. when different rate or in a different direction necessary condition for tile perception of retimll: image changes are "matched," than the eye movement, predictably lead object movement. An afterimage viewed in constancy is predicted, and when those to perceived movement. Os reported the dark by an 0 moving his eyes appears changes are not "matched," some change whether or not they saw a visual target to move (Mack & Bachant, J969), but in visual perception is predicted. Constancy move when the movement of the target there is no retinal movement. A moving is predicted when retinal image changes are was either dependent on and simultaneous object in an otherwise empty fJeld, accounted for in terms of 0 movement with their eye movements or when the accurately pursued by the O's eyes, appears information. Constancy here signifies the target movement was independent of their to move, but there is no retinal movement. perception of stability in the visual field, eye movements. In the main experiment, A stationary scene viewed by moving eyes i.e., objects in the visual field appear to observations were made when the ratio appears stationary despite retinal image maintain their positions despite between eye and target movement (em/tm) movements (position constancy). The displacements of the retinal images. was 2/5. 1/5, 1/10, 1/20, and O. All these existence of these and other phenomena Failures of constancy refer to those ratios were tested when the direction of suggests that the relationship between occasions in which image displacements of the target movement was in the same (H+), retinal image movement and perceived stationary objects lead to perceived opposite (H-), and at right angle's to movement is more complex. A theory that movement in the visual field. (V+, V-) the movement of the eye~ t:ve attempts to specify the relationship The postulation of some sort of movements, target movements, and reports between image or stimulus displacements comparator mechanism provides a concept of target movement were recorded. Results and perceived movement has been that allows us to account for many of the indicate that a discrepancy between eye variously referred to as a cancellation, facts of movement perception. There is and target movement greater than 20% discounting, compensating, or now considerable evidence supporting the predictably leads to perceived target taking-into-account theory of movement operation of this sort of mechanism during movement, whereas a discrepancy of5% or perception (von Holst, 1954; Mackay, head movements. Information about head less rarely leads to perceived movement. 1967; Rock, 1966; Teuber, 1960). movements appears to mediate the The results are interpreted as support for If we are permitted to overlook the relationship between visual displacement the operation of a compensatory subtle and not so subtle differences and perceived movement (Wallach & mechanism during eye movements. between the various statements of this Kravitz, 1965; Wallach & Frey, 1969; Hay, theory, it becomes possible to set out its 1968; Rock, 1966). In these studies, What is the basis of perceiving the main outlines. All forms of this theory are abnurmal visual displacements, movement of a single object in an in agreement that retinal image changes displacements that are either faster, slower, otherwise unstructured visual field? The alone can neither account for the or in a different direction than the O's own most obvious answer is that it is the occurrence of movement perception nor head movements and do not simply reflect movement of the retinal image that is alone determine whether the movement the 0 movement, predictably led to crucial,3 since with every movement of an perceived resides in the object or in the O. perceived object motion. Until now there object there is a corresponding movement It is a theory that accounts for perceived has been no available evidence that a of the image of that object across the object motion as well as the failure to comparator operates during eye retina of the O. This answer is the more perceive object motion despite movements. Since the eyes are rarely still attractive since there is now ample displacements or changes in the retinal and since we generally see our visual evidence that vertebrate nervous systems image. It assumes, in fact, that these are environment as stationary despite the are well endowed with receptor cells correlative events. The theory asserts that constant displacements of the retinal uniquely sensitive to retinal movements. If, the basis ofperceived object motion resides images produced by the fairly constant however, retinal displacement were the in the relationship between the behavior of movements of the eye, it would appear central factor in perceiving object the retinal image and the available sensory that some kind of comparator mechanism movement, it would follow that every time information about the movement of the o. in fact operates during eye movements.4 there was retinal movement greater than It assumes the existence of some kind of Yet in the only completely reported the threshold of the detecting cell central mechanism, a comparator experiment examining the relationship mechanisms, object movement· would be (von Holst, 1954) that takes into account, between eye movements, image perceived, and in its absence, no such matches, compares, or evaluates retinal movements, and the perception of movement would be seen. image shifts with reference to information movement (Wallach & Lewis, 1965) the It is, of course, a well·known fact that about 0 movement. The theory assumes authors conclude that target movements the case is not so simple. There are too that if not accounted for or matched by are not assessed in terms of eye many instances of perceived movement in appropriate 0 movements, retinal image movements. By devising a situation in the absence of retinal movement and of the displacements will invariably lead to the which the 0 saw a projection of his own Perception & Psychophysics, 1970, Vol. 8 (SA) Copyright 1970, Psychonomic Journals, Inc., Austin, Texas 291 pupil, the authors produced abnormal target motion. Unfortunately the account approximately 2 mm in diam, were displacements of a visual target dependent given is brief and no details are included. recorded by one channel of the pen on eye movements. This technique made it The contradiction between the Wallach recorder. Simultaneous recording of eye possible to produce a situation in which and Lewis results and those briefly and target trace movemertt permitted a the target disk, the projection of the pupil, reported by Yarbus made further continuous check on the relation between could be made to move at either a slower examination of the relationship between eye and target movement. The volume or faster rate than the eye itself. Their eye movement, image movement, and control knob was calibrated from 0 to I. results indicate that abnormal target perceived movement necessary. Another When this knob was set at 0, the trace was dis p lacements accompanying eye reason for such a study is the fact that an not moved at all by eye movements. When movements, do not reliably cause reports eye- m()ve me n t/ im age -m ove men t this knob was set at 1, the trace moved the of perceived target movement. They comparator capable of doing nothing more same amount as the eyes and thus could conclude: "Our results are incompatible than merely discriminating between approximate a stabilized image (Le., when with the view that the apparent rest of instances of eye movements that are either the direction of trace displacement and eye visual objects whose images shift due to accompanied or not accompanied by movement were the same). When the knob eye movements is to be explained by a retinal displacements would make it very was set at some point between 1 and 0, the compensating process which takes the eye difficult to account for any perception of trace moved some fraction of the amount movements into account." movement during eye movements. the eyes moved. Thus, when the knob was From the Wallach and· Lewis results it By a technique different from that used set at 2/5, the target trace moved 2/5 of might be possible to argue that all by either Wallach and Lewis or Yarbus, a the distance that the eyes moved. (All de tection of retinal displacement is situation was created in which eye calibrations were frequently checked.) The suppressed during eye movements. If this movements were accompanied by increase in what is best described as trace were the case, then, since no retinal abnormal image displacements, that is, jitter with increase in gain were mostly displacements would be registered during displacements that did not directly reflect eliminated by filtering. What jitter an eye movement, there would be no the movements of the eye. Os reported remained was accounted for in the reason to expect a loss of position whether or not the target at which they experimental design. constancy during eye movements, and were looking appeared to move. A switch on the control panel permitted there would be no reason to postulate rapid shifts from the horizontal to the some kind of comparator that could match METHOD vertical input channels of the oscilloscopes.