The surface and deep structure of the waterfall illusion.

The surface structure of the waterfall illusion or motion aftereffect (MAE) is its phenomenal visibility. Its deep structure will be examined in the context of a model of space and motion perception. The MAE can be observed following protracted observation of a pattern that is translating, rotating, or expanding/contracting, a static pattern appears to move in the opposite direction. The phenomenon has long been known, and it continues to present novel properties. One of the novel features of MAEs is that they can provide an ideal visual assay for distinguishing local from global processes. Motion during adaptation can be induced in a static central grating by moving surround gratings; the MAE is observed in the static central grating but not in static surrounds. The adaptation phase is local and the test phase is global. That is, localised adaptation can be expressed in different ways depending on the structure of the test display. These aspects of MAEs can be exploited to determine a variety of local/global interactions. Six experiments on MAEs are reported. The results indicated that relational motion is required to induce an MAE; the region adapted extends beyond that stimulated; storage can be complete when the MAE is not seen during the storage period; interocular transfer (IOT) is around 30% of monocular MAEs with phase alternation; large field spiral patterns yield MAEs with characteristic monocular and binocular interactions.