comparison of typicality judgments of learning-disabled and nonlearning-disabled children

Typicality judgments refer to the extent to which items are thought to be typical of their language categories. For example, an apple is a typical fruit, whereas a kiwi is an atypical one. Typicality judgments help reveal a person's level of word knowledge and concept development. The theory of category prototypes (Posner, 1969) gave rise to the assessment of the typicality judgments of children and adults. The two main purposes of this study were to provide typicality norms for learning disabled (LD) children, and to clarify the nature of the differences between learning disabled and nondisabled (NLD) students regarding their word knowledge and categorization skills. A total of 210 subjects participated in the study; 180 were public school children (grades 2, 4, 6) from Palm Beach County, Florida. Half of these students attended part-time classes for the learning disabled while the other half were enrolled in regular classrooms. All children had achieved IQs in the average range of intelligence. The remainder of the subjects (30) were adult college students at Florida Atlantic University in Boca Raton. All subjects were asked to determine whether each of 125 words were category members, and if they were, how well each one exemplified the particular category in question. Categories included birds, clothing, vegetables, fruit, and four-footed animals. Results revealed that the LD children knew the meanings of fewer category items, included fewer appropriate words as category items, and were less adultlike in their rankings of words that were included as category members. Although both LD and NLD children's word rankings became more adultlike with age, the LD children's pattern of progression differed. For LD children, typicality ratings became significantly more adultlike between grades four and six, whereas the NLD subjects demonstrated significantly improved ratings between grades two and four. This different pattern illustrated a developmental lag in word knowledge for the LD children.