Conditions for the detection of coherent motion

Previous studies have suggested that human motion perception involves at least two different detection stages: an orientation selective or component motion stage and a combination stage where selectivity to the coherent motion of a pattern, e.g. a plaid is established. These studies are inconclusive as to the motion detection process per se. Here we provide evidence that the motion detectors involved are of the correlation type. We determined critical values for the temporal and spatial modulation of the stimulus structure where the motion of the stimulus is no longer visible. Our results indicate that the spatial parameters of plaid- and component-motion detectors are identical but that the critical temporal modulation period is shorter for plaid-motion detectors. The results are discussed with respect to recent neurophysiological and psychophysical evidence for the two-stage motion detection model.