Retinal image smear as a source of information about magnitude of eye movement.

A number of experiments were conducted to determine to what extent retinal image smearing during saccades provides information about the eye movement magnitude to the perceptual system.The technique involved obtaining measures of perceived movement when the total visual field was displaced in conjunction with saccadic eye movements.Trials with normal retinal smear were compared with trials on which smearing was greatly reduced or eliminated.The results are interpreted as showing that the absence of normal retinal smear during a saccade increases the uncertainty in the information available to the perceptual system and that this uncertainty results in a tendency to perceive smaller than veridical amounts of movement.Questions concerning the source of extraretinal information about eye position available to the perceptual system, and questions concerning the accuracy of such information, have been with us at least since Helmholtz (1867/1962).Accurate information about eye position might possibly be provided by input to the perceptual system from the muscle spindles or tendon organs of the extraocular muscles.Two major kinds of observation, however, persuaded Helmholtz that this was not the case.He pointed out that if a person with a paralyzed external rectus muscle of the right eye tries to move that eye to the right (left eye occluded), he sees the visual world jump to the right.In short, he perceives as if his eye did move to the right, and since the retinal image did not change, the world must have moved.If adequate "inflow" information were available to the perceptual system from the muscles that move the