A preference for visual speed during smooth pursuit eye movement

Does the preference for visual speed extend to motion perception when the eye moves? Current evidence from psychophysics and neuroscience is limited to small patches of image motion and stationary fixation. Active observers, however, are more likely to use large patches of retinal flow and extra-retinal signals accompanying eye movement to judge motion. We therefore investigated whether speed remains a primary dimension during smooth pursuit using a ‘discrimination-contour’ technique. Our results showed that observers struggled most when trying to discriminate pursued stimuli that travelled at the same speed but moved over different distances and durations. This remained the case when retinal flow was added, and when we isolated trials in which extra-retinal signals were the only salient cue to motion. Our results suggest that preferential sensitivity for visual speed is quite general, supported by the many different types of motion mechanism used by active observers