Knowledge enrichment and conceptual change in folkbiology: evidence from Williams syndrome.

Ten participants with Williams syndrome (WS) (average verbal mental age of 11;5) were compared to two groups of normally developing children (average mental ages 10;11 and 6;7 years) with respect to intuitive biological knowledge about people, animals, and plants. Participants in the older control group were individually matched to the participants with WS on verbal mental age. The probes for biological understanding were drawn from the existing literature on the development of folkbiology and were divided into two batteries based on the hypothesized distinction of (1) general knowledge consistent with the conceptual repertoire of normally developing preschool children (the T1/T2-Neutral Animal Knowledge battery) and (2) folkbiological concepts normally acquired between ages 6 and 12 which require conceptual change for their construction (life, death, people-as-one-animal-among-many, species kind as determined by origin of the animal; the T2-Dependent battery). The two task batteries were equated for task demands, differing only in the content of the concepts probed. It was hypothesized that if this distinction is a false one, and the construction of folkbiology is accomplished entirely by enrichment of the preschooler's knowledge, there should never be a population with differential performance on these two batteries. People with WS were nonetheless found to be differentially impaired on the T2-Dependent battery. They performed at the level of the older control group on the T1/T2-Neutral battery, but at the level of the 6-year-olds on the T2-Dependent battery. These data support the distinction between two types of conceptual knowledge acquisition: acquisition of new knowledge formulated over an existing conceptual base (enrichment), on the one hand, and knowledge acquisition that results in genuine conceptual change, on the other. The implication of these results for a precise characterization of how concepts of people with "cocktail party syndrome" may be "superficial" is also discussed. Copyright 1998 Academic Press.