Figure ground segregation modulates perceived direction of ambiguous moving gratings and plaids

A translating oriented grating viewed through a circular aperture with an o ccluding area in the middle appeared to move alternately in an oblique or i n a vertical direction depending on the foreground/background assignment on the central occluding area. The effect occurred even when the central area was simply removed from the display, thus giving rise to a 'subjective' oc cluder. Parametric studies revealed that the probability of seeing oblique or vertical motion was affected by the size of the central area but not by its contrast relationships with the grating. Similar phenomena of ambiguous motion direction were observed using changes in colour along a translating grating that produced neon colour spreading effects, or using oriented edg e discontinuities that collapsed into subjective plaids composed of two one -dimensional gratings. These results are discussed with respect to the hypo thesis that surface segmentation mechanisms play a crucial part in the inte rpretation of motion signals. (C) 1998 Elsevier Science Ltd. All rights res erved.