Visual jitter: evidence for visual-motion-based compensation of retinal slip due to small eye movements

When dynamic random noise is replaced by static noise after a period of adaptation, adjacent unadapted regions filled with static noise appear to 'jitter' coherently in random directions for several seconds, actually mirroring the observer's own eye movements of fixation [Murakami, I. & Cavanagh, P. (1998). Nature, 395, 798-801]. The present study aims at psychophysically locating two distinct stages underlying this visual jitter phenomenon: a monocular, adaptable stage that measures local retinal motion and a compensation stage that estimates a baseline motion minimum and subtracts it from motion vectors nearby. The first three experiments revealed that visual jitter has storage, directional selectivity, and spatial frequency selectivity, like the motion after-effect does. These results suggest some overlap in the adaptation mechanisms for the two effects, possibly at or below the level of primary visual cortex. The next two experiments revealed the transfer of the effect across the vertical meridian as well as the existence of a preferred stimulus size that is a linear increasing function of eccentricity, mimicking the RF size of the monkey MT neurons. These results suggest that some extrastriate motion area along the parietal pathway including MT mediates motion-based compensation of retinal slip.