Performance of retarded and nonretarded persons on information-processing tasks: Further tests of the similar structure hypothesis.

Abstract

In this article we review information-processing studies applicable to the similar structure hypothesis. This hypothesis holds that when nonorganically impaired retarded and nonretarded persons are similar in general developmental level, they are also similar in the cognitive processes and concepts by which they reason. Results of this review were strikingly different from those of an earlier review focusing on Piagetian investigations. A meta-analysis revealed that the performance of retarded groups was significantly inferior to that of their nonretarded psychometric mental age peers. We also found a significant relation between the mental age of the subjects and the probability of finding a significant difference between retarded and nonretarded subjects. A number of alternative explanations are offered for these findings. When a mentally retarded child and a younger nonretarded child are at the same level of cognitive development, say at the same mental age, how similar are the processes by which the two children reason? For the past two decades this question has been a central issue in a sometimes heated debate—one with significant implications for the study of both mental retardation specifically and cognitive development generally. This debate is called the developmental versus difference controversy. On one side of the controversy is the developmental position, advanced by Zigler (1969) and elaborated by Weisz, Yeates, and Zigler (1982). This position, which applies only to individuals not suffering from organic impairment, holds that retarded and nonretarded people pass through cognitive developmental stages (e.g., the stages described by Piaget, 1964, 1970) in an identical order, but differ in rate and upper limit of development. Retarded children are said to traverse the stages more slowly and attain a lower developmental ceiling than nonretarded children. According to the developmental position, retarded and nonretarded children who are equated for level of development (most often operationally defined as psychometric mental age [MA]) will not differ in the cognitive processes by which they reason. On the other side of the controversy is the difference position, held by several theorists. One tenet of this position is that the