Perceived size and motion in depth from optical expansion
The research investigated the perceived motion in depth resulting from the optical expansion or contraction of objects. A theoretical analysis of this cue was made in terms of the size-distance invariance hypothesis. For presenting stimuli, a computer simulation was developed which simulated the physical motion in depth of a constant-sized object at a constant velocity. A series of experiments showed that the extent of perceived motion in depth did not relate to the change in perceived stimulus size as predicted by the size-distance invariance hypothesis. Instead, substantial perceptions of depth motion occurred even though the ratio of the terminal perceived sizes was similar to the ratio of the terminal visual angles. Extending past research, a theoretical account based on the existence of two distinct processes involved in responding to size and distance was applied successfully. One process expressed by the size-distance invariance hypothesis determines the response to immediate, sensorily specified information. The second process involves the effect of size remembered from a previous perception (off-sized judgments) upon the response to distance. As determined by measurement obtained from using the head motion procedure, this remembered (representational) size, as it occurs in successive instants of the optical expansion pattern, can be translated by the visual system into a robust perception of distance.