Perceptual effect of pursuit eye movements in the absence of a target

Abstract

THE traditional explanation¹ of visual tracking has been that smooth tracking by the eyes depends on the presence of a moving retinal image at or near the fovea. However, evidence is steadily accumulating suggesting that this explanation is incomplete². The presence of an extrafoveal afterimage or stabilised retinal image in certain circumstances suffice to initiate smooth tracking movements^3–5; observers are able to track, in the dark, the position of their own hand⁶ or of a moving sound source⁷ and may, after considerable practice, be able to generate sinusoidal tracking movements purely voluntarily^4,8. We describe here a perceptual effect apparently created by the generation of smooth horizontal tracking eye movements, in the absence of a target, by observers regarding a display of dynamic visual noise. We interpret this effect in terms of the presence within random visual noise of features which lead to the neuronal representation of movement at some unspecified level of organisation of the visual system.