Twins: Patterns of cognitive development as measured on the Wechsler Preschool and Primary Scale of Intelligence.

Abstract

Cognitive patterning and development was appraised for 142 pairs of twins at 4, 5, and 6 years of age, based on their test scores on the Wechsler Preschool and Primary Scale of Intelligence. Compared with the singleton norms, the twins showed an initial lag at age 4, with Verbal IQ being somewhat more depressed than Performance IQ, By age 6, however, the twins had fully recovered their deficit on both scales and reached parity with singletons. Monozygotic twins displayed relatively high withinpair correlations for Verbal IQ and Performance IQ, and even higher correlations for Full Scale IQ. Dizygotic twins displayed moderate within-pair correlations for the IQ scores, and most were significantly lower than the monozygotic correlations. Further analysis showed that monozygotic twins were also significantly more concordant for the differences between Verbal IQ and Performance IQ, and for the patterning of the subtest scores. Measures of family socioeconomic status and parental education correlated .2S-.32 with the twins' IQ at age 6. The results led to the inference that within a broad range of home environments, the genetic blueprint made a substantial contribution to cognitive patterning and development. Mental development in the preschool years is characterized by the rapid expansion of cognitive abilities which gradually develop into the attribute called intelligence. While infancy is largely dominated by sensorimotor processes, there appears to be a significant transition after age 2 years to the more