Perception of random-dot symmetry and apparent movement at and near isoluminance

There have been conflicting reports on whether apparent movement in random-dot kinematograms is abolished at isoluminance. The present results suggest that it is, provided that dynamic (uncorrelated) surrounds are used, and the subject has to report the shape of the target rather than the presence of movement in an isolated portion of the target. On the other hand, perception of random-dot symmetry is still possible at isoluminance. The reason for this difference appears to be the need for exact-position information in movement but not symmetry perception. Control experiments suggest that the effects are not due to artefacts such as chromatic aberration in the eye.