Moving and motion adaptation
The motion aftereffect is an enduring favourite of vision science. It is normally thought synonymous with adapting an observer to a period of image motion, using stimuli that range from cavalry to waterfalls, from scrolling TV credits to moving gratings and dots. Here I show an alternative route, one that emphasises repetitive eye movement not the stimulus that produced them. The resulting illusory motion cannot be explained in terms of direct adaptation to image motion but rather two separate eye-movement mechanisms. The first is low-level and associated with the control system itself. This mechanism explains why illusory motion seen following eye movement changes direction and why, unusually, reflexive eye movement produces an aftereffect that does not 'store' across a period of darkness. The second is more intriguing. Our experiments imply that eye movement is an indirect means of adapting mechanisms more usually thought sensitive to image motion. It does so using an important link between the eye-movement system and cortical motion-processing centres. This new type of motion aftereffect might therefore inform us about fundamental processes associated with perceiving motion during eye movement, emphasising that aftereffects are not just simply about neural fatigure but play a more functional role.