Deaf people who are deprived of linguistic experience during the formative years seem to provide a unique opportunity to psychologists concerned with the language-cognition relationship. Empirical studies of deaf people's performance on nonverbal cognitive tasks were reviewed. Deaf were found to perform similarly to hearing persons on tasks where verbal knowledge could have been assumed a priori to benefit the hearing. Such evidence appears to weaken a theoretical position which attributes to language a direct, general, or decisive influence on intellective development. The poorer performance of the deaf on some tasks is parsimoniously attributed to either lack of general experience which is no longer manifest by adulthood or to specific task conditions which favor linguistic habits.

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About 200 children, age 5–11, from three different regions in Southern England were interviewed about their understanding of social events: school, store, money, payment, the community and government, some specific jobs, and acquisition of a role. Seven characteristics of thinking about the ‘impersonal’ social world were proposed and illustrated by interrelated evidence. To most 5- to 6-year old children the world ‘out there’ appeared: (1) undifferentiated (minimal role and individual differences); (2) personalized (voluntaristic); (3) everything occurs according to known rules (no contingencies); (4) conflict-free (happy); (5) with easy access to money; (6) ego-typical (own experience is the norm), and (7) focused on external aspects. Four substages of social understanding were proposed as showing a developmental progression: (1) arbitrary-personalized with imaginative elaborations; (2) primitive functional differentiation; (3) part systems of social functions, and (4) coherent global system. While substage 4 eliminates major ‘childish’ discrepancies due to a global conceptual framework – analogous to Piaget’s concrete operations – it does not indicate any deep understanding of society’s structure which is probably reserved for adolescents and adults with specialized interests and the capacity for formal operations. Implications of these findings for educational and social planning were discussed.

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Recent studies with deaf subjects are reviewed, grouped into subareas of rule learning, logical symbols, Piaget-type, memory, and perception. Comparative results on hearing controls are reported with a view to isolate the potential effects of linguistic deficiency on cognitive performance. The general conclusions of a previous review are confirmed in that the thinking processes of deaf children and adolescents are found to be similar to hearing subjects. It is pointed out that with few exceptions persons profoundly deaf from birth are severely deficient in linguistic skills in spite of many years of schooling; verbal processes could therefore not account for the emergence of cognitive skills even where developmental lags were noted. Occasional failures on certain logical tasks could be parsimoniously attributed to an unfavorable environment such as is observed in culturally different groups. The reviewed data challenge existing theories that base intellectual development largely upon linguistic learning; on the other hand, they confirm Piaget's operative theory.