The importance of differentiation in young children's acquisition of expertise.

In a short-term longitudinal study, stories told about novel creatures conveyed information varying in its capability for differentiating. Depending on the context, a bodily feature could be functionally undifferentiated (FUF), meaning that its subtypes (e.g., eyes of two forms) shared a generic function ("seeing"), or functionally differentiated (FDF), meaning that each subtype's function was unique to it (e.g., only a "hooded eye" could "see in a sandstorm"). 5- to 6-year-olds who heard 8 stories, but not those who heard only 4, cited FDFs more than FUFs in a pair-justification test of judged similarity; and their delayed recall of specific story events was greater when FDFs rather than FUFs were involved. In the absence of direct instruction, young children show sensitivity to the degree of differentiation afforded by feature-function relations.