Overview of Variables Believed to Be Correlates of High Performance IQ

A survey of research results of variables believed to be correlates of high P-IQ, covered in Chapter 8 as well as this chapter, provides little in the way of empirical validation. Patients with left-hemisphere lesions are anticipated to have P > V profile, but in most studies they do not. Patients with temporal lobe epilepsy in the left hemisphere, who undergo left lobectomies, display a decided postoperative P > V pattern on Wech-sler's adult scales, including the WAIS-III, but within the neuropsychological literature, that is pretty much it. Across instruments and studies, based on more than 1,300 patients with left lesions, the P > V profile is only 3^ points. But that number is inflated by data obtained on old studies with the old Wechsler-Bellevue. Subtract those studies, and focus on the WAIS and WAIS-R investigations, and the P > V profile for N = 967 patients with left-hemisphere damage is an unimpressive 2 points.

The research reviews with adolescents and adults are no more compelling for several other variables long believed to be associated with high Performance IQ. Individuals with learning disabilities are defined more by their high and low areas of functioning when Wechsler subtests are regrouped by Bannatyne's system or by acronyms (e.g., ACID) than by V-P IQ discrepancy. Individuals with mental retardation do not show consistent P > V profiles, and neither do those with Autistic Disorder (especially if they are high functioning). Although Wechsler's children's scales, including the WISC-III, frequently yield substantial P > V patterns for Hispanic individuals, data from the WAIS-III reveal only small P > V IQ discrepancies, especially when Hispanics and other ethnic groups are matched on age, gender, and education; indeed, when these other variables are controlled, the POI > VCI difference is only about 1 point. American Indians do display a substantial P > V profile for children and adults, but studies with adult samples are sparse, and nonexistent for the WAIS-III.

In general, none of the variables that are supposedly associated with high Performance IQ have been adequately validated for adult samples, and certainly not for the WAIS-III. The profile of four factor indexes holds the most hope for future research investigations, particularly because these indexes effectively subdivide both the Verbal and Performance scales into their major component abilities.

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