Relative Distance Perception Through Expanding and Contracting Motion and the Role of Propriospecific Information in Walking

Two experiments using a new device that correlates simulated optic flow with forward and backward head motions are reported. The first experiment tested the effectiveness of the rate of optical expansion/contraction as a cue for relative distance perception; the second experiment examined the role of propriospecific information in determining whether or not a simulated wall was perceived to be moving relative to the ground. In walking along the line of sight in a stationary environment, the image of a nearer object expands/contracts more than the image of objects farther away. In Experiment 1, observers’ abilities to judge which of two walls was nearer, according to expanding/contracting patterns, were tested. The results show that both walking and stationary observers can detect the order of depth from expansion patterns but not from the contraction patterns. Experiment 2 assessed the role of propriospecific information for specifying the motion or nonmotion of a simulated “wall” relative to the ground. The results show the importance of synchrony between expansion/contraction patterns and head motion. Whether or not an observer is obtaining information actively does not seem to matter for perceiving relative distance but it does matter in perceiving object motion.