UC Davis

The present study is an in-depth examination of receptive vocabulary in individuals with Down syndrome (DS) in comparison to control groups of individuals of similar nonverbal ability with typical development (TD) and non-specific etiology intellectual disability (ID). Verb knowledge was of particular interest, as it is known to be a predictor of later syntactic development. Fifty participants with DS, aged 10-21 years, 29 participants with ID, 10-21 years, and 29 participants with TD, 4-9 years, completed measures of receptive vocabulary (PPVT-4), nonverbal ability (Leiter-R), and phonological memory (Nonword Repetition subtest of the CTOPP). Groups were compared on percentage correct of noun, verb and attribute items on the PPVT-4. Results revealed that on verb items, the participants with ID performed significantly better than both participants with DS and TD, even when overall receptive vocabulary ability and phonological memory were held constant. Groups with DS and TD showed the same pattern of lexical knowledge, performing better on nouns than both verbs and attributes. In contrast, the group with ID performed similarly on nouns and verbs, but worse on attributes.