Learning Count Nouns and Adjectives: Understanding the Contributions of Lexical Form Class and Social-Pragmatic Cues

In two experiments, one hundred ninety-two 3-year-olds, 4-year-olds, and adults heard a novel word for a target object and then were asked to extend the label to one of two test objects, one matching in shape-based object category (the shape match) and the other matching in a property other than shape (the property match). We independently manipulated the lexical form class cues (count noun, adjective) and social-pragmatic cues (point actions, property-highlighting actions) accompanying the label. The impact of these two types of cue on extension differed markedly across age groups. Adults and 4-year-olds extended the word to the property match significantly more often when the term was modeled as an adjective and when it was presented with property-highlighting actions; but adults extended both adjectives and count nouns systematically to the property match when the speaker highlighted the non-shape property, whereas 4-year-olds systematically extended only adjectives to the property match under these conditions. Three-year-olds extended the word to the property match significantly more often when the label was modeled as an adjective but were not significantly affected by the social-pragmatic cues; and they failed to extend either adjectives or count nouns systematically to the property match when the speaker highlighted the non-shape property. We discuss the results in terms of the proposal that word learning draws on cues from multiple sources and the nature of the “shape bias” in lexical development.