Interaction of scene background, size change, direction and velocity in determining perceived motion in depth

Abstract

Gibson (1950) contrasted ground theory in which distance judgments are made for objects seen against a continuous background surface with air theory in which isolated objects are seen against a homogeneous background. The present study examined the effects of three sources of distance information with objects displayed against a real world scene background or a uniform background. Observers were presented with two displays in sequence and asked to select the display in which the final position of a spherical object was closer. The object either varied in projected size or maintained a constant size and either moved downward in the projection or moved only horizontally. Objects that moved downward either maintained a constant 3-D velocity or a constant projected velocity. Size change was effective in indicating motion in depth for both background conditions, but the effect of vertical motion was different for the two background conditions. With a homogeneous background, objects moving only horizontally were judged as moving closer and the different velocity functions did not significantly affect judgments. With a scene background, judged motion in depth was smallest for objects moving only horizontally. Objects moving at a constant 3-D velocity were judged as approaching closer than objects moving at a constant projected velocity. These results show an interaction of the presence or absence of a ground surface with size and motion information, with changing size effective independently of the background but the effect of motion direction and velocity strongly dependent on the presence of a scene background.

Footnotes

 NIH AG13419-06