Symbol -mediated perceptual processing in children (Homo sapiens) and chimpanzees (Pan troglodytes)

The cognitive prerequisites for successful categorization have been the focus of intense research. Prior studies have demonstrated both perceptual and conceptual strategies of categorization. The extent to which language impacts these strategies is debatable. An ideal investigation of this issue would control for the presence of language by studying individuals with a language system compared to those without such a system. The current investigation examines the role of language in categorization both within and across species by comparing chimpanzees (Pan troglodytes), a species capable of acquiring some sort of language system, to human children. Two separate experiments were performed with chimpanzees (both non-language trained and language trained) and two groups of human children in order to control for the presence of language. The effects of language on categorization were assessed through the use of a matching task containing items with both known and unknown labels. Additionally, other features of items were manipulated such as perceptual similarity, familiarity with items, and level of category (subordinate level versus basic level) in an attempt to determine which strategies individuals used when matching items. In Experiment 1, two groups of children (30 and 36 months) participated in an identical categorization task that involved picking matching photographs. Results indicate that language does not play a strong role in children's categorization strategy; rather, familiarity with items seems to influence conceptual categorization to a greater extent. Furthermore, children are able to flexibly use both perceptual and conceptual strategies of categorization. In Experiment 2, two groups of chimpanzees (non-language trained and language trained) were tested in a similar matching paradigm. Results indicate that both groups of chimpanzees use perceptual and conceptual strategies of categorizing. Moreover, labels may adversely affect conceptual categorization in chimpanzees. Comparisons between children and chimpanzees and implications for future research are discussed.