The curvature of the background affects the perception of 3D object motion
36.449, Sunday, May 12, 2:45 - 6:45 pm, Orchid Ballroom
Junjun Zhang1, Myron Braunstein2, George Andersen3; 1George Washington University, 2University of California, Irvine, 3University of California, Riverside
Optical contact with a flat background is important for the perception of object location in a 3D scene (Meng & Sedgwick, 2001, 2002) and for the perception of 3D object motion with cast shadows (Kersten, 1997). In the present study, we investigated the effect of background curvature on the perceived trajectory of an object moving in a 3D scene. In the first experiment, observers were presented with a sphere moving in a horizontal plane at eye level against a grid background. The trajectory of the sphere was concave, convex or straight, indicated by changes in its angular size and angular speed during the motion sequence. The background was flat or curved in the horizontal direction, with concave or convex curvature indicated by the spacing of the horizontal and vertical grid lines. Observers were asked to judge the direction of the spheres motion (convex or concave). The results showed that the judged curvature of the objects motion depended almost entirely on the direction of curvature of the background. In the second experiment, observers were presented with two displays on each trial, differing in both the amount of curvature of the motion path and the amount of curvature of the background. Both curvatures were in the same direction (either convex or concave). The observers were asked to judge which display showed the more curved motion path. Judgments of the curvature of the sphere's motion were largely determined by the curvature of the background, with the motion path of an object judged as more curved when it was displayed against a more curved background. Our results clearly indicate that, when an object is moving against a curved background, both the perceived direction and the perceived amount of curvature of the object's trajectory depend primarily on the curvature of the background.