Segregation of spatially superimposed optic flow components.

The transparency phenomenon, which arises when a radial and a rotational motion pattern are spatially superimposed, suggests that these motion patterns are processed independently. Indeed, for unrestricted stimulus durations, observers could identify the rotational pattern as clockwise or counterclockwise, and the radial pattern as expansion or contraction, even under uncertainty. However, when the time available to process the compound stimulus was equal to the minimum duration required to identify each of the patterns when presented in isolation, identification was impaired. Whereas for spirallike motion patterns the radial and rotational components could be identified, radial and rotational motion patterns were not processed independently when superimposed. Although radial and rotational transformations could not be identified simultaneously, a coherent optic flow pattern could be segregated from another superimposed optic flow component given definite foreknowledge.