The illusory brightening MAE separates low-level motion models.

Abstract

The brightening MAE provides a challenge to low-level motion models. Introduced by Anstis (1967, Science 155 710-712), uniform fields appear to brighten after adaptation to repeated darkening. When the uniform test field is replaced by a spatial gradient, observers report illusory motion. We first measured the apparent speed of the aftereffect. Observers adapted to a circular pattern of linearly lightening or darkening radial segments, which were later replaced by static luminance gradients. When brightening or darkening, the adjacent segments of the dynamic pattern were set to grey so that any local motion energy at the boundaries was balanced over the adaptation period. At test, the sign of the spatial gradient was chosen appropriately for each segment to deliver uniform rotational motion. We found that the perceived speed of the rotation was precisely inversely proportional to the spatial gradient, as predicted by a spatiotemporal gradient motion computation. Motion energy models employ spatially band-pass front-end filters and therefore will not respond to uniform fields (the even Gabor is an exception). However, if the temporal brightening and spatial luminance gradient were combined before motion analysis, motion at test might be predicted by alternative models. To separate the models we sculpted the profile, introducing non-zero higher-order spatial derivatives. We now observed an apparent slowing of the aftereffect, which increased in turn with the accumulation of higher orders of spatial derivative for both convex and concave luminance ramps. Crucially, computer simulation shows the energy model and the multichannel gradient model predict increased speed from a simple addition of temporal brightening and the test spatial pattern. The data however are consistent with an isolated spatially low-pass first temporal derivative component delivering brightening, divided by multiple spatial derivatives introduced in the test pattern, a previously proposed multichannel gradient architecture, resulting in slowing of perceived speed.Meeting abstract presented at VSS 2014