Comparison of effects of eye movements and stimulus movements on striate cortex neurons of the monkey.

AN IMAGE MOVES with respect to the retina both when our eves move a nd when the object moves, but in one case we perceive a stationary object, in the other case a moving object. How can we tell the difference? One approach to this question was proposed by Helmholtz (10) over a century ago. He suggested that when efferent impulses go to the eye muscles, other impulses go simultaneously to areas within the brain. The impulses to the brain would indicate that an eye movement is occurring and that movement of the image with respect to the retina is due to movement of the eye and not to movement of the object. W. James (12) vigorously disputed this hypothesis, but similar hypotheses have been suggested to explain how an insect differentiates between its own movement and movement generated by external forces (1 1), why salamanders make continuous circling movements after eye rotation (Is), and how stability of perceived space is maintained in man (19). The impulses from a motor area to a sensory system have been referred to as a “corollary discharge” (18, 19). I f such a corollary discharge exists, one would expect to see a difference at some point in the visual system in the neural response depending on whether the retina moves past a stationary image or whether the image moves across a stationary retina. The purpose of the present experiments was to see whether in striate cortex neurons there is any difference between the response to rapid eye movements across a stationary stimulus and the response to rapid stimulus movements across a stationary eye. A brief report of these experiments has been published previously (22).