Measurable biological substrates to verbal-performance differences in Wechsler scores

The use of intelligence tests and the interpretation of verbal-performance differences has been criticized as not being useful in the classification, treatment planning, or placement of children. As a result, some professiona ls have suggested that intelligence testing does not provide useful theoret ical or clinical information. The purpose of this article is to provide a g eneral review and discussion of studies relating to hemispheric asymmetry, particularly asymmetry of the planum temporale in normal and reading disabl ed populations and possible implications with regard to the meaningfulness of IQ test results. A great deal of neurobiological research has examined t his region of the brain because it has long been recognized for its role in linguistic processing. Specifically, the planum temporale has consistently been found to be associated with language comprehension and has been the f ocus of multiple clinical and experimental studies. Although Wechsler (1978 ) never anticipated that research would reveal the neuropsychological basis of intelligence, recent research specific to Verbal IQ (VIQ), the Verbal C omprehension (VC) factor, and verbal-performance (V-P) differences as measu red by the Wechsler Intelligence Scale for Children-Third Edition (WISC-III ) suggests otherwise. This research suggests that both the VIQ and VC facto r of the WISC-III are related to the length of the left temporal bank of th e planum temporale. Based on these studies, V-P differences may reflect the asymmetry of the planum. With advanced technology and functional neuroimag ing, further research may provide information relating to how these finding s can be useful in clinical practice.