Still Searching a Cluttered Scene

M.J. Bravo and H. Farid

Vision Sciences (VSS), Sarasota, FL, 2004

Purpose: Most of the research on visual search and recognition has used isolated objects presented on uniform backgrounds. It is unclear whether the conclusions from this work generalize to cluttered scenes. For example, in sparse displays, global shape is thought to play a central role in recognition. Background clutter may obscure global shape, however, and so we expect that in clutter, local cues such as color will play a larger role.

Methods: Each search stimulus contained 12 photographs of ordinary objects. These objects were either arranged sparsely (well-separated on a uniform grid) or arranged as clutter (randomly positioned and often overlapping). On each trial, observers were first presented with a category name (animal, vehicle, food). Their task was to locate a member of that category in the search stimulus. This target often overlapped other objects, but was itself never occluded. To measure the effect of color, the stimuli were presented in their original color, in grayscale, or in a hue-shifted color.

Results: In the uniform condition, response times did not differ for the original-color, grayscale, and hue-shifted stimuli. In the clutter condition, however, response times were about 20% faster for the original-color stimuli than for the grayscale and hue-shifted stimuli.

Conclusions: In sparse stimuli, global shape is such a reliable cue for recognition that color plays a minimal role. In clutter stimuli, however, global shape is less reliable and so local cues like color have increased importance. (Color might also be expected to facilitate segmentation in the clutter stimuli, but the similar response times for hue-shifted and grayscale stimuli did not support this prediction.) This result, in conjunction with our results from last year, indicates that the processes underlying recognition and search may differ significantly for sparse and cluttered scenes.