Sign vocabulary in deaf toddlers exposed to sign language since birth.

Lexical comprehension and production is directly evaluated for the first time in deaf signing children below the age of 3 years. A Picture Naming Task was administered to 8 deaf signing toddlers (aged 2-3 years) who were exposed to Sign Language since birth. Results were compared with data of hearing speaking controls. In both deaf and hearing children, comprehension was significantly higher than production. The deaf group provided a significantly lower number of correct responses in production than did the hearing controls, whereas in comprehension, the 2 groups did not differ. Difficulty and ease of items in comprehension and production was similar for signing deaf children and hearing speaking children, showing that, despite size differences, semantic development followed similar paths. For signing children, predicates production appears easier than nominals production compared with hearing children acquiring spoken language. Findings take into account differences in input modalities and language structures.