Perceived velocity of point-light walkers under complex viewing and background conditions

Abstract

An experiment with a computer-generated display of nine moving dots representing a human walker (Cutting, 1978) was carried out. The independent variables were the observer's perspective (stabilized or mobile), the background (vertical gratings with spatial frequencies of 0.2, 0.4, and 0.8 cycles/deg), the movement of the background (-1, 0, 1, 2, and 4 cycles/s), and the objective velocity of the walker. The dependent variable was the velocity estimated by the observer. It was predicted that the mobile observer's perspective should lead to a more precise estimate of the walker's velocity, because there were more motion cues available. There were 10 observers and their data were analyzed individually. Five observers perceived the walker's velocity faster under the mobile observer's perspective, three showed the opposite result, and two observed no significant difference. This large variability was attributed to the ambiguity of motion cues when there is no direct information available about the distance of the background from the moving object. © 2005 Japanese Psychological Association. Published by Blackwell Publishers Ltd.