Thompson, Lashley, and Spearman: Three Views of the Biological Basis of Intelligence

Thompson, Lashley, and Spearman: Three Views of the Biological Basis of Intelligence FRANCIS M. CRINELLA State Developmental Research Institutes 2501 Harbor Boulevard Costa Mesa, Ca Iifornia 92626 An important problem for the empirical psychologists of a century ago was the differentiation of human from non-human intelligence.lJ The strategy they adopted to demonstrate interspecific differences involved (1) establishing a plausible definition of “intelligence,” (2) developing tests of the construct which could be performed by a number of species, and (3) arraying the performances of the different species according to test This approach rarely yielded a clear phylogenetic progression of test performances, although a few notable successes have been rep~rted.~J For most of the twentieth century, American comparative psychology has been rooted in Thorndike’s conclusion of 1898 that there are no qualitative interspecific differences in i n t e l l e ~ t . ~ In . ~ retrospect, failure to validate this basic tenet of Darwinism appears to have been due to longstanding disagree- ments over the nature of intelligence in the human animal, much less in infrahu- man species. Over time, the search for a consensual operational definition of the construct in animals was largely abandoned and replaced by investigations of specific components of the behavioral repertoire, as represented in paradigms such as classical conditioning, maze learning, passive avoidance and the like. In the process of exploring these areas, one of the experimental methods that emerged was the induction of brain lesions to produce variability in perfor- mance, a practice that came to be called ‘‘neuropsychology.”loJ1 Karl Lashley is generally considered the founder of that subdiscipline of experimental psychol- ogy.12 INTELLECTUAL RETARDATION At the turn of the century, empiricism was introduced into the study of mental retardation with the objective investigations of Binet and Simon.13 Despite the contemporaneous emergence of neuropsychology and the scientific study of mental retardation, few early investigators drew parallels between animals with experimentally induced brain lesions and mentally retarded hu- mans. There were several reasons why these lines of inquiry failed to converge, the two most important being that there had never been an agreed-upon opera- tional definition of intelligence in non-human species, and that the investigation of defective performance in animals was typically confined to a limited set of laboratory tasks, thereby constraining inferences that a general intellectual loss