FIRST-ORDER AND 2ND-ORDER MOTION PERCEPTION IN GABOR MICROPATTERN STIMULI - PSYCHOPHYSICS AND COMPUTATIONAL MODELING

This paper examines the perception of first-and second-order motion in human vision. In an extension of previous work by Boulton and Baker [ J.B. Boulton, C.L. Baker, Motion detection is dependent on spatial fre quency not size, Vision Res., 31 (1991) 77-87; J.B. Boulton, C.L. Bake r, Different parameters control motion perception above and below a cr itical density, Vision Res., 33 (1993) 1803-1811], the direction of tw o-frame apparent motion is measured for stimuli composed of Gabor or G aussian micropatterns. Three conditions are investigated. Condition 1 is that used by Boulton and Baker, in which motion is defined by the d isplacement of Gabor micropatterns. In condition 2, motion is defined by the displacement of Gaussian micropatterns. In condition 3, the env elopes of Gabor micropatterns are displaced while their carriers remai n static. Using sparsely distributed micropatterns, direction judgemen ts in all three conditions are determined by the spacing of the microp atterns. With a dense stimulus, direction judgements vary as a functio n of displacement in qualitatively different ways for the three condit ions. The psychophysical results are predicted by a two-channel comput ational model. In one channel, motion is calculated directly from stim ulus luminance, while in the other it is preceded by a texture-grabbin g operation. The relative activities of the two channels dictates whic h governs direction judgements for any given stimulus. (C) 1998 Elsevi er Science B.V.