Differentiating global and local contour completion using a dot localization paradigm

Abstract

Competing theories of partially occluded object perception (amodal completion) emphasize either relatively local contour relationships or global factors such as symmetry. These disparate theories may reflect 2 separate processes: a low-level contour interpolation process and a higher-order global recognition process. The 2 could be distinguished experimentally if only the former produces precise representations of occluded object boundaries. Using a dot localization paradigm, we measured the precision and accuracy of perceived object boundaries for participants instructed to complete occluded objects with divergent local and global interpretations. On each trial, a small red dot was flashed on top of an occluder. Participants reported whether the dot fell inside or outside the occluded object's boundaries. Interleaved, 2-up, 1-down staircases estimated points on the psychometric function where the probability was.707 that the dot would be seen as either outside or inside the occluded object's boundaries. The results reveal that local contour interpolation produces precise and accurate representations of occluded contours, and consistency across observers, but completion according to global symmetry does not. These results support a distinction between local, automatic contour interpolation processes and global processes based on recognition from partial information.