What factors need to be taken into account when conducting and interpreting intellectual assessments in neurological impaired patients?

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What factors need to be taken into account when conducting and interpreting intellectual assessments in neurological impaired patients?

Intelligence is a concept that encompasses many mental ablilities. Researchers have tried to define the core features of intelligence and have come up with many different definitions. Binet and Simon (1905, as cited in Kamphaus, Winsor, Rowe & Kim, 2005) defined intelligence as “the ability to judge, understand and reason well”. Perhaps the most widely referenced and enduring definition comes from David Wechsler (1939), who described intelligence as “the aggregate or global capacity to act purposefully, to think rationally, and to deal effectively with the environment” (p. 3). Since then, scientists have attempted to integrate different researchers’ ideas and find a consensus definition. A fairly recent definition comes from "Mainstream Science on Intelligence", which was signed by 52 intelligence researchers in 1994. They regard intelligence as “very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings -- "catching on," "making sense" of things, or "figuring out" what to do.” (Gottfredson, 1997, p. 13). For a better understanding of how intelligence can and should be assessed a short introduction is given into different theories of intelligence. This is followed by a brief description of the the most widely used intelligence tests. Subsequently, theoretical issues of assessing patients’ intellectual abilities are outlined such as the need for a standard condition (premorbid intelligence). Finally, a number of factors are discussed that are specific to conducting tests with brain-damaged patients.  

As intelligence tests incorporate current theories into their design, some aspects of psychological interpretations of intelligence need to be understood. The most influential approach to understanding intelligence is the psychometric approach. It is based on psychometric testing, which typically establishes an intelligence quotient (IQ). The traditional view is that this score reflects a general intelligence factor “g”. Others (e.g., Thurstone, 1938, as cited in Lezak, 1995) do not agree with one general score and focus on more specific group factors such as memory, verbal comprehension, spatial visualisation, or number facility. Some researchers (e.g., Catell, 1987 as cited in Ferrer & McArdle, 2004) consider g as part of a two-part construct, consisting of gF and gC, which stand for fluid intelligence and crystallized intelligence. Fluid intelligence includes the capacity to learn and solve problems independent from culture and verbal skills, while crystallised intelligence is highly culturally dependent and helps solving tasks that require learned and habitual responses. While some theorists regard the concepts of IQ and g as firmly established, others (e.g. Gardner, 1983) are critical of the psychometric approach. They argue that to base a concept of intelligence on test scores alone is to ignore many important aspects of mental ability. Gardner (1983) emphasizes some of these aspects in his multiple intelligences approach. He includes for example musical and bodily-kinaesthetic and various forms of personal intelligence in his theory. While Gardner's arguments have attracted considerable interest, the stability and validity of performance tests in these new domains has yet to be demonstrated. There is also some to doubt whether some of these abilities (e.g., bodily-kinesthetic) are appropriately described as forms of intelligence rather than as special talents. Robert Sternberg's (1985, as cited in Sternberg, 2005) triarchic theory of intelligence proposes three fundamental aspects: analytic, creative, and practical, of which only the first is measured to any significant extent by mainstream tests. His investigations suggest the need for a balance between analytic intelligence, on the one hand, and creative and especially practical intelligence on the other. In line with this, other investigators have demonstrated the relative independence of academic and practical intelligence. Brazilian street children, for example, were found to be quite capable of doing the math required for survival in their street business even though they have failed mathematics in school (Carraher, Carraher, and Schliemann, 1985). The fact that there is little agreement among researchers about what to include into the concept of intelligence emphasizes the need to be very cautious when interpreting IQ test results.

The most widely used instruments to assess intellectual functioning are the Stanford-Binet Intelligence scales, the Kaufman Adolescent and Adult Intelligence Test, and the Wechsler Intelligence Scales. The Stanford-Binet scale measures the five cognitive factors knowledge, fluid reasoning, quantitative reasoning, visual-spatial processing and working memory. The newest edition measures these five factors in the verbal as well as in the non-verbal domain (Roid & Pomplun, 2005). The Kaufman Intelligence test measures learning, memory, simultaneous processing, planning and knowledge. A strength of the Kaufman tests is that they are the only measure that assesses a person’s ability to learn new information and apply this information to new, more complex situations. (Kaufman et al., 2005). The most frequently used test batteries are probably the Wechsler Intelligence Scales (WIS, current version Wechsler Adult Intelligence Scale- WAIS-III). The Wechsler test battery consists of eleven different tests. Six of them are classified as verbal tests (Information, Comprehension, Arithmetic, Similarities, Digit Span and Vocabulary). They are thought to measure verbal reasoning and attention to verbal materials as well as aquired knowledge. The other five tests were termed performance tests. They include Digit-Symbol Coding, Picture Completion, Block Design, Picture Arrangement and Object Assembly and are thought to measure spatial processing, attention to visual detail, and visuomotor integration. Most of these tests contain similar items at different levels of difficulty. This allows relatively fine graded measurement and comparison of performances between the different WIS tests. The sum of all eleven scores is used to calculate a full scale score, which has been found to be an excellent predictor of academic achievement. The WIS scales have been found to be reliable and valid instruments for comprehensive assessment of general cognitive functioning. Therefore clinicians use them as one of the key instruments for the assessment and diagnosis of, for example, developmental disorders such as mental retardation or learning disability; cognitive giftedness; neuropsychological disorders such as traumatic brain injury; Alzheimer’s disease; multiple sclerosis; and alcohol related disorders such as Korsakoff syndrome (e.g., Tulsky et al., 2003).

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Some researchers, however, question the usefulness of these tests for neuropsychological assessment. Although much of the behaviour that intelligence tests measure is directly referable to certain cognitive functions, these functions most often overlap and cannot be investigated separatly. Much research has focused, for example, on a comparison between the different WIS scores (verbal, performance and full) in an attempt to isolate impairment in one or the other major functional system to aid diagnosis. This attempt has not been very successful for several reasons. Tests in each scale differ considerably in their sensitivity to both, general effects such as mental ...

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