THE PERCEIVED DIRECTION OF TEXTURED GRATINGS AND THEIR MOTION AFTEREFFECTS

The stimuli in these experiments are square-wave luminance gratings wi th an array of small random dots covering the high-luminance regions. Owing to the texture, the direction of these gratings, when seen throu gh a circular aperture, is disambiguated because the visual system is provided with an unambiguous motion energy. Thus, the direction of tex tured gratings can be varied independently of grating orientation. Whe n subjects are required to judge the direction of textured gratings mo ving obliquely relative to their orientation, they can do so accuratel y (experiment 1). This is of interest because most studies of one-dime nsional motion perception have involved (textureless) luminance-define d sine-wave or square-wave gratings, and the perceived direction of th ese gratings is constrained by the aperture problem to be orthogonal t o their orientation. Thus, direction and orientation have often been c onfounded. Interestingly, when subjects are required to judge the dire ction of an obliquely moving textured grating during a period of adapt ation and then the direction of the motion aftereffect (MAE) immediate ly following adaptation (experiments 2 and 3), these directions are no t directly opposite each other. MAE directions were always more orthog onal to the orientation of the adapting grating than the corresponding direction judgments during adaptation (by as much as 25 degrees). The se results are not readily explained by conventional MAE models and po ssible accounts are considered.