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A THEORY OF VISUAL STABILITY ACROSS SACCADIC EYE MOVEMENTS

Bridgeman, Bruce , van der Heijden, A.H.C. and Velichkovsky, Boris M (1994) A THEORY OF VISUAL STABILITY ACROSS SACCADIC EYE MOVEMENTS.

Short Abstract:

We identify two aspects of the problem of how there is perceptual stability despite an observer's eye movements. The first, visual direction constancy, is the (egocentric) stability of apparent positions of objects in the visual world relative to the perceiver. The second, visual position constancy, is the (exocentric) stability of positions of objects relative to each other. We analyze the constancy of visual direction despite saccadic eye movements. Three information sources have been proposed to enable the visual system to achieve stability: the structure of the visual field, proprioceptive inflow, and a copy of neural efference or outflow to the extraocular muscles. None of these sources by itself provides adequate information to achieve visual direction constancy; present evidence indicates that all three are used. Our final question concerns the information processing operations that result in a stable world. The three traditional solutions involve elimination, translation, and evaluation. All are rejected. From a review of the physiological and psychological evidence we conclude that no subtraction, compensation or evaluation need take place. The problem for which these solutions were developed turns out to be a false one. We propose a "calibration" solution: correct spatiotopic positions are calculated anew for each fixation. Inflow, outflow, and retinal sources are used in this calculation: saccadic suppression of displacement bridges the errors between these sources and the actual extent of movement.

Long Abstract:

We identify two aspects of the problem of how there is perceptual stability despite an observer's eye movements. The first, visual direction constancy, is the (egocentric) stability of apparent positions of objects in the visual world relative to the perceiver. The second, visual position constancy, is the (exocentric) stability of positions of objects relative to each other. We analyze the constancy of visual direction despite saccadic eye movements. Three information sources have been proposed to enable the visual system to achieve stability: the structure of the visual field, proprioceptive inflow, and a copy of neural efference or outflow to the extraocular muscles. None of these sources by itself provides adequate information to achieve visual direction constancy; present evidence indicates that all three are used. Our final question concerns the information processing operations that result in a stable world. The three traditional solutions involve elimination, translation, and evaluation. All are rejected. From a review of the physiological and psychological evidence we conclude that no subtraction, compensation or evaluation need take place. The problem for which these solutions were developed turns out to be a false one. We propose a "calibration" solution: correct spatiotopic positions are calculated anew for each fixation. Inflow, outflow, and retinal sources are used in this calculation: saccadic suppression of displacement bridges the errors between these sources and the actual extent of movement.

Keywords:	space constancy, proprioception, efference copy, space perception, saccade, eye movement, modularity, visual stability
Subjects:	Neuroscience: Neural Modelling Psychology: Perceptual Cognitive Psychology Psychology: Physiological Psychology Psychology: Psychobiology Psychology: Psychophysics
ID code:	bbs00000437
Deposited by:	Bruce Bridgeman on 01 May 2001