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Questions and Answers
Question # 11
Does a Wechsler Verbal IQ>Performance IQ deviation of significant proportions signal the presence of NLD and/or right cerebral hemisphere dysfunction?
A conceptual error made by some clinical neuropsychologists is to consider symptoms and signs of disturbance in isolation from the context of the results of a comprehensive neuropsychological evaluation. This is particularly counterproductive in the case of NLD because one "symptom" of the syndrome (i.e., a Verbal IQ well in excess of a Performance IQ) can occur as a result of disturbances that have nothing to do with the NLD syndrome, white matter perturbations, or right hemisphere dysfunction.
For example, such a discrepancy may be seen in individuals who, for one reason or another, adopt a slow-but-accurate strategy on the Wechsler Performance "speeded" subtests (i.e., ignore the instructions to perform as quickly as possible). So too, persons with lower motor neuron disease and other afflictions that affect dexterity, but not higher cognitive functions, may obtain very low scores on the Performance scale; the same scenario, mutatis mutandis, obtains for the hard-of-seeing.
The list of reasons for doing poorly on the Wechsler Performance
scale relative to the Verbal scale could go on and on. The important
issue to bear in mind with respect to the analysis of the NLD syndrome
is the following: All or virtually all of its elements should be
present if the dynamics of the syndrome are to be clarified, and if
forms of treatment that are thought to be suitable for persons who
exhibit NLD are to be instituted with confidence.
Finally, some of the results of two recent investigations have a bearing on this issue. First, Pelletier, Ahmad, & Rourke (2001, and see Question #10) examined data from 89 carefully diagnosed/classified 9- to 15-year-old children with NLD. We found the following: only 27% of the children with NLD exhibited VIQ>PIQ by 10 points or more; 78% exhibited 2 of their highest scores on the Verbal scale on the Information, Similarities, or Vocabulary subtests; and, 77% exhibited 2 of their lowest scores on the Performance scale on the Block Design, Object Assembly, or Coding subtests. In a subsequent study by Drummond et al. (2005, and see Question #10) of 10 carefully diagnosed/classified 7- to 8-year-old children with NLD, we found the following: 70% of the children with NLD exhibited VIQ>PIQ by 10 points or more; 80% exhibited 2 of their highest scores on the Verbal scale on the Information, Similarities, or Vocabulary subtests; and, 90% exhibited 2 of their lowest scores on the Performance scale on the Block Design, Object Assembly, or Coding subtests.
School Psychologists and others who are involved in setting criteria for classification of NLD might wish to take special note of these results. Of particular concern should be the finding in the Pelletier et al. (2001) investigation that only 27% of the children between 9 and 15 years of age with NLD exhibited a Verbal>PIQ discrepancy of 10 points or more. This would imply that using this fairly crude measure as the sole criterion for further consideration of NLD for a child at this age level would rule out roughly 73% who exhibit the syndrome. Use of this criterion in this manner for 7- and 8-year-olds would be expected to preclude consideration of some 30% who exhibit NLD at this age level (Drummond et al., 2005).
The issue of "right hemisphere dysfunction" and its relationship to NLD will be clarified in subsequent questions within this section.
Drummond, C. R., Ahmad, S. A., & Rourke, B. P. (2005). Rules for the classification of younger children with Nonverbal Learning Disabilities and Basic Phonological Processing Disabilities. Archives of Clinical Neuropsychology, 20, 171-182.
Pelletier, P. M., Ahmad, S. A., & Rourke, B. P. (2001). Classification rules for Basic Phonological Processing Disabilities and Nonverbal Learning Disabilities: Formulation and external validity. Child Neuropsychology, 7, 84-98.
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