Pii: S0010-0277(00)00100-1

We examined the time-course of the in ̄uence of background knowledge on perceptual categorization by manipulating the meaningfulness of labels associated with categories and by manipulating the amount of time provided to subjects for making a categorization decision. Extending a paradigm originally reported by Wisniewski and Medin (1994) (Cog. Sci. 18 (1994) 221), subjects learned two categories of children's drawings that were given either meaningless labels (drawings by children from `group 1' or `group 2') or meaningful labels (drawings by `creative' or `non-creative' children); the meaningfulness of the label had a signi®cant effect on how new drawings were classi®ed. In addition, half of the subjects were provided unlimited time to respond, while the other half of the subjects were forced to respond quickly; speeded response conditions had a relatively large effect on categorization decisions by subjects given the meaningless labels but had relatively little effect on categorization decisions by subjects given the meaningful labels. These results suggest that some forms of background knowledge can show an in ̄uence at relatively early stages in the time-course of a categorization decision. q 2000 Elsevier Science B.V. All rights reserved.