Effects of stimulus similarity on perceptual and conceptual comparisons.

Abstract

Subjects were to judge as rapidly as possible whether pairs of geometric designs were the same or different on a given relevant dimension (size, shape, or color). Response times varied depending on the number of values on nonrelevant dimensions shared by the comparison stimuli (stimulus similarity). “Same” responses were facilitated by stimulus similarity, regardless of whether the stimuli were perceptually available for comparison or available (identified by verbal labels) only for conceptual or memorial comparison. “Different” responses were slowed by similarity in the perceptual task, but facilitated in the conceptual task. An experimental manipulation that permitted the subjects to identify the comparison stimuli prior to a memorial comparison did not change the basic similarity function. The data were generally more consistent with an activation rather than with a search/retrieval theory of short-term memory. A descriptive linear model with two similarity-dependent parameters for response competition and semantic distance effects gives a close account of the data.