Family influences on the cognitive development of profoundly deaf children: exploring the effects of socioeconomic status and siblings.

We evaluated the cognitive development of 48 profoundly deaf children from hearing families (born 1994-2002, mean age M = 8.0 years at time of test, none of whom had received early auditory-verbal therapy) as a function of family socioeconomic status and number of siblings. Overall, the deaf children matched a younger group of 47 hearing controls (M = 4.6 years) on verbal ability, theory of mind, and cognitive inhibition. Partial correlations (controlling for age) revealed positive relations in the hearing group between maternal education and inhibition, between number of younger siblings and references to emotions, and between number of close-in-age siblings and references to desires and false beliefs. In the deaf group, there were positive relations between household income and memory span, between maternal education and references to false beliefs, and between number of younger siblings and nonverbal ability. In contrast, deaf children with a greater number of older siblings aged ≤12 years showed inferior memory span, inhibition, belief understanding, picture-sequencing accuracy, and mental-state language, suggesting that they failed to compete successfully with older siblings for their parents' attention and material resources. We consider the implications of the findings for understanding birth-order effects on deaf and language-impaired children.