Perceived speed of motion in depth is reduced in the periphery

The perceived speed of motion in depth (MID) for a monocularly visible targ et was measured in central and peripheral vision using a 2AFC speed discrim ination task. Only binocular cues to MID were available: changing disparity and interocular velocity difference (IOVD). Perceived speed for monocular lateral motion and perceived depth for static disparity were also assessed, again in both central and peripheral vision. The purpose of the experiment was to assess the relative contributions of changing disparity and IOVD cu es to the perceived speed of stereomotion. Although peripheral stimuli appe ared to lie at approximately the same depth as their central counterparts, their apparent speed was reduced. Monocular/lateral and binocular/MID speed s were reduced to a similar extent. It seems that reduced apparent monocula r speed leads to reduced perceived MID speed, despite the fact that the dis parity system appears to be unaffected. These results suggest that the IOVD cue makes a significant contribution to MID speed perception. (C) 2000 Pub lished by Elsevier Science Ltd.