More on the Effects of Early Manual Communication on the Cognitive Development of Deaf Children

Three groups of Israeli deaf children ages 6 to 14 and a group of hearing children were compared on intelligence. The three deaf groups were (a) 23 deaf children with deaf parents and deaf siblings (DpDs)—heredity as cause of deafness, manual environment; (b) 76 deaf children with hearing parents and deaf siblings (HpDs)—heredity, partial manual environment; and (c) 144 deaf children with hearing parents and siblings (HpHs)—no heredity, oral environment. Three measures of cognitive development were used: teachers' evaluations, the Draw-a-Person Test, and the Snijders-Oomen Non-Verbal Test. The DpDs children were superior to other deaf children and comparable to hearing children on most intelligence measures. Results showed that the manual environment factors, and not heredity, are responsible for the cognitive superiority of deaf children of deaf parents.