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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).

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 slowing , and to specific effects such as verbal, visuo-spatial or memory impairments. Sometimes impairments in only one or two of the tests in a scale could be informative but they are easily obscured by the averaging processes with other tests in the scale (Botez, Ethier, Leveille, & Botez-Marquard, 1977). On the other hand, one has to be careful with interpreting single test results on their own because impaired performance in only one test could also be due to chance. In addition, it was found that overall IQ scores on standard tests cannot directly predict the size of brain lesions (Maher, 1963). Discrete brain lesions can produce deficits over a broad range of cognitive functions and these functions can be affected with different severity. Degenerative diseases and aging lead to differential deterioration of diverse cognitive functions and the affected functions decline at different rates. Although IQ tests are to some extent able to measure general cognitive ability when the brain is intact, the fact that they measure a mixture of performances which cannot easily be disentangled limits their use for neuropsychological assessment. (Lezak, 1995)

To be able to draw valuable inferences regarding the current IQ score of a patient it is necessary to compare it to some measure that indicates what this patient’s performance was like before the brain damage. A premorbid IQ score has to be calculated. The current / premorbid difference in IQ can be an informative tool for clinicians in determining whether the individual has sustained loss of functioning as a result of the accident or illness. Based on the finding that language is relatively robust and remains constant when other cognitive abilities (e.g. memory, reasoning, arithmetic skills) are declining, vocabulary and reading tests were chosen as an index for premorbid functioning. Yates (1956, as cited Zhu & Weiss, 2005) was the first person to argue that premorbid functioning could be estimated with the WAS Vocabulary score since it was found to be relatively independent from age-related decline in performance. Later research (Rusell, 1972), however, showed that individuals with brain damage performed much more poorly on vocabulary than the general population. Therefore, reading tests mainly replaced vocabulary tests as an index for premorbid functioning. Nelson and O’Connell (1978 in F) introduced the National Adult Reading Test (later New Adult Reading Test or NART), which contains a list of words, all of which are irregularly pronounced (e.g. ache, aisle, chord, etc.). They developed a regression-based formula for estimating WAIS- IQ scores from the scores on NART and concluded that predictions based on NART were fairly accurate. However, recently concerns have been raised about its robustness and the possible influence of scorer biases. Further, the method has been questioned as it underestimates the premorbid ability of dementia patients (Stebbins, Wilson & Gilley, 1990). An alternative method to determine premobid functioning uses the relationship between Wechsler IQ scores and demographic variables such as age, education, sex, race, and occupation (Heaton, Ryan, Grant, & Mathews, 1996). The correlation between current IQ scores and demographic variables is then used to develop prediction equations to determine premorbid IQ scores. The most recent approach is a new word-reading test, the Wechsler Test of Adult Reading (WTAR), which uses words that are phonetically difficult to pronounce and would require previous learning. The WTAR was found to correlate highly with other reading tests and IQ scores obtained with WAIS. Moreover, it has been conormed directly with the Wechsler scales, which reduces variablity due to other factors when comparing current and premorbid IQ scores (Zhu & Weiss, 2005).

So far only theoretical issues concerning neuropsychological assessment and interpretation were covered. When assessing brain damaged patients intellectually, there are, however, a number of practical issues that have to be taken into consideration. First, there are general factors that might affect performance of patients as well as of healthy people. These include culture, socio-economic status (SES), temperament, age, education, genetics or individual interests (lec notes). Age has a particularly pronounced effect on IQ scores. Therefore, scores should always be adjusted for age (as for example in WAIS-III). Secondly, there are factors that affect performance particularly in brain damaged patients. Brain damage often leads to personality and emotional change, most commonly to disinhibition, anxiety, hypersensitivity, emotional dullness or altered social awareness (Parikh & Robinson, 1987, as cited in Lezak, 1995). Further, obsessive-compulsive traits often evolve; patients can be more irritable, restless, have a lower frustration tolerance or be simply apathic (Heilman, Bowers & Valenstein, 1993).

Mental activity variables, which influence the efficiency of mental processes such as attention and concentration, are among the most common mental problems of brain damaged patients (Lezak, 1989 as cited in Lezak, 1995). Attentional deficits can have an effect on performance on almost every cognitive function tested. Many patients have a reduced auditory attention span, which results in that they hear only part of what was said, particularly when the task is complex. Other patients have difficulty keeping track of their ongoing mental activities, which often shows in repetitions on list learning tasks. Some patients have problems with executive functions such as switching between different tasks that are required in the test procedure. A further problem related to attentional deficits is increased distractibility. That is, some patients are easily distracted by their surrounding and have problems focusing on the task, which can subsequently interfere with cognitive performance and learning (Aks & Coren, 1990). In such cases the examiner should attempt to provide a test environment that is as sterile as possible (e.g. clocks should be quiet and out of sight, ideally room should be soundproof). If, however, the patient got distracted by for example a loud noise during a timed task it might be preferable to repeat the test on another day. In addition, the examiner should document attentional lapses when they occur since this could be further explored to obtain information about the patients abilities/inabilities.

A typical observation when testing brain damaged patients is that they fatigue easily, especially when they are still in the acute phase of the trauma. Examiners must be alert to detect fatigue because patients might not report it or might not be aware of it. That is examiners should look out for slurring in speech or restlessness. It is therefore crucial that patients are tested at an optimal time of the day (preferably the morning). Sometimes the patients fatigue might require the examiner to stop testing. Most tests can be continued on subsequent days. In addition, patients with cerebral impairments can vary noticeably in their performance from day to day or even from hour to hour. The examiner should attempt to test these patients on their “good days”. That is, when they feel confident and alert for the examination (Smith, 1993).

Fatigue and attentional deficits are often related with frustration and depression. When patients notice their frequent errors they might get frustrated, which in turn lowers their motivation and discourages them. This can carry over even into tests on which the patient would be normally good at. The examiner should encourage the patient whenever possible and should deliberately ensure that the patient has some success, even if the impairment is extensive. These factors put high demands on the clinician who is administering the tests because they have to find a balance between optimal and standard conditions. Creating optimal conditions is aimed at obtaining the best test performance the patient is capable of producing. However, these should not be too far away from standard conditions, which are necessary for many tests to allow a meaningful interpretation of individual differences.

Most often patients taking neuropsychological tests are on drug medication for their disorder. The effect of medication on cognitive functioning is multifaceted. For example, the anticholinergic action of some drugs used in Parkinson’s Disease and depression might interfere with memory functions (Vollhardt et al., 1992 as cited in Lezak, 1995). Brain damage can also interfere with drug effects, making them less predictable than for intact people (Eames et al., 1992 as cited in Lezak, 1995). Examiners should be aware that some patients take time to adjust to a new drug, which can alter their mental efficiency.

As mentioned above, intellectual assessment of patients most often involves a comparison between the current and the premorbid IQ score. Of all the previously mentioned factors that can affect test results, the examiner should be most cautious with those that affect the two IQ scores (current and premorbid) differently. That is, factors such as culture or SES will most likely affect tests scores to an equal extent, while attentional and fatigue problems will probably be more pronounced in the more demanding tests of current IQ. Since the current versus premorbid IQ difference is taken as a measure of the extent of functional impairment due to brain damage, its correct interpretation has wide implications for rehabilitation and therapy.

When using IQ tests to determine the extent to which general cognitive functioning is compromised after brain damage (e.g. due to stroke or traumatic brain injury) it is also important to consider impairments in other domains (e.g. sensory deficits). It is a fact that brain damage very rarely affects only single structures; in the majority of cases several functions are impaired simultaneously. Poor performance in IQ tests can therefore be due to specific impairments such as hearing and visual deficits, neglects or aphasia. Patients with these deficits might have the ability to perform well in IQ tests but are unable to do the tasks because of another concurrent impairment. It is therefore important not to evaluate intelligence performance on its own but in conjunction with other tests to rule out possible underlying deficits.

A recent approach to improve intellectual assessment, especially in problem patients, (e.g. patients with memory, attention, comprehension or executive function deficits, aphasics) is the combination of standard test batteries with neuroimaging methods such as event-related potentials (ERPs). ERPs can measure sensory, perceptual and cognitive processing that reflects speech processing, reading, attention, memory, concept formation, and expectancy. The main advantage is that ERPs can measure these processes independent of overt behaviour and verbal activity. Standard neuropsychological assessment tasks can be adapted for computer presentation and the electro-encephalogram (EEG) can be recorded simultaneously. The patient’s brain responses hence substitute for behavioural or verbal responses enabling accurate neuropsychological assessment or treatment monitoring. A study by O’Connolly, Major, Allen , & D'Arcy in 1999 investigated performance on WISC-III with ERPs in healthy adults and claims to provide evidence for the efficacy of this new method for neuropsychological assessment. Du Rouseau (2006) correlated IQ scores from the Wechsler scale with EEG data and found that neural efficiency, increased brain complexity and frontal lobe syncronisation as measured with EEG was positively correlated with IQ scores. High versus low IQ scores were predicted from EEG data with 92.8 % accuracy.


Intelligence is regarded as a capacity of mind that includes many related mental abilities, such as the capacity to reason, to aquire knowledge and apply it, to plan, to solve problems, to think abstractly and to comprehend ideas and language. There is an ongoing debate among researchers about the extent to which intelligence can be measured using IQ tests. The numerous limitations of IQ tests in healthy people seem to be multiplied when looking at neurologically impaired patients. There are a range of theoretical issues that limit the use of IQ tests for neuropsychological assessment. For example, tests developed to measure IQ measure a variety of cognitive functions. Moreover, IQ scores cannot predict lesion size or site. This means IQ test scores provide only very general information about a patient’s abilities. Further, results about current abilities should always be interpreted in the context of a standard measure, which provides information about patients’ premorbid aptitudes. Despite the fact that no specific conclusions can be drawn from patients’ IQ test results, clinicians sometimes find it useful to compare premorbid and current scores to determine the extent of functional loss after brain damage. In order for these results to be meaningful, however, a number of practical issues when conducting the tests have to be considered. For example, examiners should attempt to create optimal test conditions that take patients’ limitations due to their impairment into account. In many cases IQ tests should be combined with other tests that determine possible perceptual or language impairments. New techniques such as the combination of traditional tests with simultaneous EEG recording could assist in obtaining more accurate results of patients’ actual cognitive abilities. However, due to the numerous limitations of intelligence assessment, the importance of results should not be overestimated. Rather, results should be regarded as contributing only a small piece of information to the whole picture of a patient’s history.


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