Surface versus edge-based determinants of visual recognition

Abstract

Two roles hypothesized for surface characteristics, such as color, brightness, and texture, in object recognition are that such information can (a) define the gradients needed for a 2 1 2 -D sketch so that a 3-D representation can be derived (e.g., Marr & Nishihara, 1978) and (b) provide additional distinctive features for accessing memory. In a series of five experiments, subjects either named or verified (against a target name) brief (50–100 ms) presentations of slides of common objects. Each object was shown in two versions: professionally photographed in full color or as a simplified line drawing showing only the object's major components (which typically corresponded to its parts). Although one or the other type of picture would be slightly favored in a particular condition of exposure (duration or masking), overall mean reaction times and error rates were virtually identical for the two types of stimuli. These results support a view that edge-based representations mediate real-time object recognition in contrast to surface gradient or multiple cue representations. A previously unexplored distinction of color diagnosticity allowed us to determine whether color (and brightness) was employed as an additional feature in accessing memory for those objects or conditions where there might have been an advantage for the color slides. For some objects, e.g., banana, fork, fish, and camera, color is diagnostic as to the object's classification. For other objects, e.g., chair, pen, mitten, and bicycle pump, color is not diagnostic, as such objects can be of any color. If color was employed in accessing memory, color-diagnostic objects should have shown a relative advantage when presented as color slides compared to the line drawing versions of the same objects. Also, this advantage would be magnified when subjects could anticipate the color of an object in the verification task, particularly on NO trials when the foil was of a different color. Neither an overall advantage for color-diagnostic objects when presented in color nor a magnification of a relative advantage on the NO trials in the verification task was obtained. Although differences in surface characteristics such as color, brightness, and texture can be instrumental in defining edges and can provide cues for visual search, they play only a secondary role in the real-time recognition of an intact object when its edges can be readily extracted.