The success of Ralph Reitan's career may be attributed to numerous influences, but here consideration will be given to the theoretical framework in which it emerged. As we know, Reitan was a student of Ward Halstead, and developed a strong interest in Halstead's work with a group of neurosurgeons in the development of new test procedures for assessing brain function in humans. The tests described in Halstead's Brain and Intelligence: A quantitative study of the frontal lobes (1947) and related publications (Halstead, 1951) formed the basis for Reitan's research and clinical careers. After reviewing a large number of tests Halstead identified 26 procedures, listed in his book, as a particular group of tests he characterized as potential “quantitative indicators” of “Biological Intelligence” (Halstead, 1951), and stressed the importance of the abilities these tests assessed for adaptive functioning. A factor analysis with a four factor solution based upon several of these tests became the basis of what we now know as the Halstead-Reitan Battery.
The theory developed was evolutionary or “Darwinian” in nature, and Halstead offered the view that his tests were indicators of level of adaptive function in civilized society. Based upon a survival of the fittest concept, they reflected those abilities that promoted survival on the planet. Those individuals who developed brain function that supported acquisition of these abilities were those who did not become extinct. As indicated in the title of his book, Halstead believed that this evolutionary process was largely a product of development of the frontal lobes. While the part of the theory about the frontal lobes remains unsettled (Reitan & Wolfson, 1994), there is greater agreement that Halstead's tests are particularly sensitive to brain function unlike another group of tests characterized as measuring “psychometric intelligence” that are more related to cultural influences, notably education. Reitan continued to characterize these tests as measures of adaptive behavior.
The major point developed in this presentation is that a substantial portion of Ralph Reitan's success is that he had the wisdom to recognize that Halstead's “Biological Intelligence” tests were very powerful instruments for assessing brain function, and that tests of that type differed from “psychometric intelligence” tests that were associated mainly with upbringing. Some of these tests had existed for many years, but they had not been related so coherently to the evolution of the brain and the emergence of adaptive behaviors. For example, a form of the Tactual Performance Test was used since the Civil War, but its relevance to brain function was not understood. Believers in natural selection would no doubt make the assumption that life forms emerged that did not acquire the abilities of the type assessed by these tests, and on the basis of natural selection did not survive. The clear clinical inference that can be made is that impairment of the brain systems that support “Biological Intelligence” because of damage or disease would be associated with loss of the associated behaviors. It was this inference that appeared to be the major impetus for Reitan's research vision and for the development of clinical neuropsychology in general.
Rather than pursuing a factor analytic model as initiated by Halstead, Reitan developed a form of levels of processing model of brain function as presented in Reitan and Wolfson (1993a, 1993b) starting with input and going to attention, concentration, and memory; then followed by a branching into language and visual spatial skills, a convergence to concept formation, reasoning and logical analysis leading to some form of output. Assessment of each of these levels is accomplished with a battery of tests the results of which produce inferences related to general level of performance, pathognomonic signs, patterns of performance, and interhemispheric differences. An important point to be made, however, is that Halstead's and Reitan's models used essentially the same data base, a battery of quantitative tests sensitive to various aspects of brain function and dysfunction. Perhaps more importantly was that the battery contained tests that were powerful indicators of brain function rather than simply relying on the pathognomonic sign approaches commonly relied upon by neurology, or single indicators of cognitive ability employed by those who base their assessments on single standard intelligence (IQ) tests. Crucial to this approach was the extensive use of procedures characterized as tests of Biological Intelligence, such as the Category or Tactual Performance Test.
The complete battery after Reitan's modifications contained tests of both biological and psychometric intelligence since their contrast is of major clinical significance. There are important differences in brain function between individuals who do poorly on Biological Intelligence tests in association with poor performance on psychometric intelligence as well, as commonly involved in individuals with intellectual disability (previously called mental retardation) and those with selective impairment on Biological Intelligence tests like the Category Test, with good preservation of psychometric intelligence, a pattern commonly associated with acquired brain dysfunction. Unlike other approaches to neuropsychological assessment, both Halstead and Reitan were committed to quantitative measures, although they used quantification in different ways. As indicated, Reitan was not a strong advocate of factor analysis, never using it in his research, and his thinking did not reflect Halstead's factor model. One does not see in his research or clinical work analyses presented within the framework of Halstead's factor analysis. Rather, it was based on stages of processing going from sensory-perceptual input through attention and remembering, analysis by the appropriate cerebral hemisphere and conceptual reasoning. However, the procedures used for assessment at each of these levels were quite similar, based largely on many of the tests described in Halstead's Brain and Intelligence. Reitan therefore used the concept of Biological Intelligence in his work, but in a way quite different from that of Halstead. A major unique contribution by Reitan was that of taking the Biological Intelligence concept and building with it a major system for the study of brain function using both experimental and clinical methods. What are typically two separate lines of psychological work, Reitan had the capacity to combine into a unified program.
Kurt Goldstein and Martin Scheerer
At about the same time as Halstead's book appeared, the Goldstein and Scheerer tests of abstract and concrete behavior (1941) were published. The tests constituted a battery that includes several sorting tests (Object Sorting, Color Sorting, and Color-Form Sorting Tests), a spatial-constructional test (Kohs Blocks; Kohs, 1919) and the Stick Test, a copying and memory task that was thought to assess the abstract attitude toward space, because it involves use of the stick patterns as abstract features of an abstract geometrical space. These tests were selected because they reflected various aspects of Goldstein's theory of the “abstract attitude” presented in his book “The Organism” (1939) and in the 1941 monograph. Various aspects of the abstract attitude were articulated, such as the ability to plan ahead ideationally, voluntary shifting, or, more dramatically, having an “attitude toward the possible.”
Both Ward Halstead and Kurt Goldstein recognized the capacity of these tests of abstract reasoning and problem solving to characterize brain function and its impairment. It became apparent that some abilities were, as Reitan put it “particularly sensitive to the condition of the brain.” Following acquired brain damage, some abilities did not change much regardless of severity of damage while other abilities changed dramatically. In Halstead's terminology, tests of these latter abilities were characterized as indicators of “Biological Intelligence” while to Kurt Goldstein and Martin Scheerer they assessed the “abstract attitude.” The view can be reasonably defended that both terms address the same concept and phenomena despite the differences in terminology and descriptive language.
In retrospect, the appearance of the Goldstein-Scheerer tests constituted a parallel course to that of Halstead. The terminology was different, and the epistemology was vastly different, but many of the tests themselves were very similar. Despite the theoretical differences, there was a clear confluence of agreement that common evaluation procedures sensitive to brain function and significant impairment of brain function identify largely conceptual difficulties involving abstract reasoning, concept formation, and problem solving. Goldstein and Scheerer called it impairment of the “abstract attitude,” but various terms with apparently similar meanings are used to describe this level such as “executive function” or the older term “higher cortical functions.” This view is clearly consistent with Halstead's conceptualization of the abstraction component of his concept of Biological Intelligence. Thus both Halstead and Goldstein and Scheerer had made basically the same discovery but characterized it differently. In essence, these complex tests of abstraction and reasoning are “the right stuff” for gaining an understanding of brain function and impairment. One can call them measures of “the abstract attitude” or “adaptive abilities constituting Biological Intelligence.” In my view, these terms address the same phenomenon.
In order to defend this view and relate it to the work of Ralph Reitan, it may be helpful to take a historical digression. Probably, the clearest demonstrations of capacity involving the abstract attitude or Biological Intelligence are found in the sorting tests. These tests have evolved into the Wisconsin Card Sorting and Halstead Category Tests. Although both Goldstein and Scheerer and Halstead also used other tests, the Kohs Blocks Test and Stick Test in their case and numerous other tests in the case of Halstead, the sorting tests have survived over the years and are still commonly used in contemporary versions. The history of the sorting test is very instructive. It was invented in Europe at around the time of World War II by Egon Weigl, who we would now characterize as a neuropsychologist. Weigl (1901–1979) was an associate of Goldstein and developed what became called the Gelb–Goldstein–Weigl–Scheerer Sorting Test. The test consisted of a set of common objects, used in daily life activities, which the patient had to sort in different groups, for instance, according to color, material, or how they are used. Subsequently, the test-taker has to sort them according to a new criterion and, therefore, has to shift sets. To analyze disorders in abstract behavior, Goldstein and Scherer (1941) specifically used sorting tasks. They provided detailed analytical, clinical descriptions of a number of these tasks. There was no quantitative scoring procedure because Goldstein was convinced that the abstract attitude could not be expressed in a single test score; the experimenter or clinician had to observe how the subject performed the tasks.
Continuing to trace the history, it is noted that the title of Grant and Berg's (1948) paper making one of the two first presentations of the Wisconsin Card Sorting Test called it a “Weigl type card sorting problem.” Thus, the connection to Weigl and to Kurt Goldstein with whom Weigl worked is apparent. The development of the Halstead Category Test, a form of sorting test, is generally attributed to a collaboration between Halstead and Paul Settlage (1943), who did primarily animal work on grouping behavior. However, there is an unwritten history that I learned from Joseph Zubin then at Columbia University. Zubin told me that Halstead would visit Columbia during the days of the Greystone Schizophrenia Lobotomy studies (Mettler, 1952). The Greystone investigators were interested in acquiring a sorting test, probably under the influence of Kurt Goldstein who was on the Columbia faculty, but a scoring system was needed. Esta Berg was apparently associated with the Greystone studies and a student of David Grant at the University of Wisconsin, and their collaboration produced the Wisconsin Card Sorting Test that was originally developed for the Greystone psychosurgery studies. The influence of these visits on the development of the Category Test by Halstead is unclear, but such an influence may be suspected. Thus we have a complex interinstitutional, international relationship among Weigl, Goldstein, Scheerer, Settlage, Grant, Berg, and Halstead around the sorting test. What these individuals appeared to have in common was a shared belief that the sorting test is a powerful method for eliciting a form of behavior that has high survival value and that is extraordinarily sensitive to alterations in brain function. In current terminology, the terms executive function or regulatory behaviors may express essentially the same concept. Individuals characterized this capacity differently at different times calling it “Biological Intelligence,” “Adaptive Ability,” “Executive Function,” “The Abstract Attitude” or within the context of behavior theory using a reinforcement construct, but the capacity of tests of grouping to evaluate brain function has not been questioned.
This brief history would indicate that during the 1930s and 1940s, several individuals and groups developed a new approach to assessment of brain function involving complex procedures that, while not necessarily only involving the frontal lobes, represented the higher cognitive functions we sometimes associate with the evolution of the prefrontal region in humans. Perhaps more importantly these abilities appear to have adaptive significance for the building of human civilization. In Halstead's colorful terminology, he described the frontal lobes as “the organs of civilization.” Goldstein's conceptualization was made in terms of self-realization, or functioning at an optimal level with resources available. In his colorful terminology, Goldstein said “The aim of the organism is to be.” A concrete manifestation of these considerations was the development of new procedures for assessing human brain function that evaluated adaptive, complex behaviors. Some of the tests were not new, such as the Tactual Performance Test, but were reinterpreted on the basis of their significance for brain function, taking examples from brain damaged patients. This development was a far departure from the behavioral neurology “diagram-making” assessment procedures of the 19th and early 20th centuries. These brief tests and interviews involved primarily simple skills such as basic language and perceptual and motor abilities. These procedures still form the substance of the neurological examination, but no longer constitute state-of-the-art neuropsychological assessment.
We would offer that the first phase of this development of neuropsychological analysis leading to Ralph Reitan's program was theory based, and the literature contained somewhat poetic phraseology, particularly notable in the writings of Goldstein and Halstead. Goldstein and Scheerer took a specifically qualitative approach to their work, and did not use scores or norms or other psychometric procedures. They were aware of them but had theoretical arguments against their use. Rather their work is characterized by descriptions in the form of vignettes describing phenomena displayed by patients during examination. Goldstein and Scheerer had no use for quantification at all, and their 1941 monograph describing their tests does not contain a statistical manual or scoring system. Halstead was quantitatively oriented, but was not particularly concerned with psychometric issues or the standardization of his test battery. His factor analysis, for which he is best known, used numerical test scores, but was intended to demonstrate the latent structure of his Biological Intelligence concept. While he was working on the development of a console used for administering all of the tests in an automated way before the growth of computers, it is understood that he did not have the goal of standardizing and publishing the tests for use by clinicians in clinical assessments. Indeed, I once received a letter from him telling me that the tests were not available.
Ralph Reitan's Program
Reitan implicitly recognized the power of Halstead's conceptualization and pursued his interest in Halstead's tests because he appeared to be well aware of their power and sensitivity. The uniqueness of Reitan with regard to these developments is that he was an empirical, quantitatively oriented scientist committed to use of experimental research procedures for establishment of this theoretical framework. Indeed, one of his first publications was a study of the validity of Halstead's tests (Reitan, 1955a, 1995b), followed by a plethora of papers presenting quantitative research results involving use of the Halstead-Reitan Battery in numerous applications. Early in his career he developed a reputation for basing his neuropsychological assessment work on quantitative data and relationships among test scores. He wrote his reports prior to reading the patient's history, having only demographic information. What might have appeared as idiosyncratic at the time, he did not interview the patients he was assessing and started the now common practice of having tests administered and scored by trained technicians. In our view, these rather radical changes in the customary conduct of practice were based on conceptual considerations including the belief that tests should provide objective information concerning the test-taker's status and should not be biased by the opinions contained in the medical records or even by the patient or acquaintances during the assessment. Neuropsychological tests should provide objective evidence of brain function based upon pertinent research. To support this view, Reitan launched an extensive research program in which hypotheses concerning relationships between test profiles and a variety of brain disorders could be tested. For example, there is the hypothesis that patients with recently acquired left hemisphere brain damage will have a substantially lower Verbal Weighted Score on the Wechsler intelligence scales than will patients with right hemisphere or generalized damage (Fitzhugh, Fitzhugh, & Reitan, 1962; Reitan, 1955a, 1955b). Some of Reitan's research was theoretical in nature providing an ongoing description of his neurobehavioral theories. For example, there has been a debate about whether impairment at the level of abstract reasoning is a qualitative phenomenon or on a continuum of function. The prominence of the impairment was not questioned, but there was substantial controversy concerning whether it represented a continuous dimension or was a new, emergent ability separate from concrete thinking (Reitan, 1958, 1959). In discussing differences between the abstract and concrete levels of behavior, we have the undoubtedly controversial quote from the Goldstein and Scheerer monograph: “There is a pronounced line of demarcation between these two attitudes which does not represent a gradual ascent from more simple to more complex mental sets. The greater difficulty connected with the abstract approach is not simply one of greater complexity, measured by the number of separate, subservient functions involved. It demands rather the behavior of the new emergent quality, generically different from the concrete.” (p. 22, 1941). If they are correct, the core deficit in brain disorders would be an emergent phenomenon that does not simply reflect substantial impairment of a number of basic abilities that combine into what produces the adaptive disabilities observed behaviorally.
Reitan and others have taken issue with the qualitative view of Goldstein and Scheerer, demonstrating in their research (Reitan, 1958, 1959) that patients could learn to improve performance on abstract reasoning tests, in this case the Halstead Category Test, and therefore did not have a fixed impairment involving concreteness. They could learn to abstract with practice. The answer to this argument proposed by Goldstein and Scheerer advocates is that one can produce correct answers on a purported test of abstract reasoning through concrete level information processing. This view was supported by Goldstein's case of an idiot savant in which the subject solved analogies tests using word association (Scheerer, Rothmann, & Goldstein, 1945) and more definitively in a study of the Category Test by Simmel and Counts (1957) in which it was shown that successful performance on this test could be achieved, at least in part, by associative learning without identifying the relative concepts. Wilner (1964) and Goldstein (1962) developed verbal analogies tests that could identify whether an item could be solved by verbal association or whether it required conceptual analogical reasoning.
This debate continues and constitutes a major controversy in the field of clinical neuropsychology regarding quantitative vs. qualitative approaches to the study of brain function and dysfunction. Some hold the view that the conceptual level is an emergent phenomenon, because impairment can be found at that level without any evidence of impairment at the other levels. Thus, for example, a patient can do poorly on the Wisconsin Card Sorting Test, with no predictive indications of impairment at the other levels discussed here. That is, the individual may have normal attention, memory, language and other basic abilities. Others believe that conceptual reasoning and tests for assessing it can be quantitatively scored as they can be for other abilities. Ralph Reitan was a strong advocate of the quantitative view.
The perspective on these matters being proposed is that Reitan was in strong agreement with his teacher Halstead and with cognitively oriented neuropsychologists notably Goldstein and Scheerer concerning what constitutes an adequate neuropsychological assessment that is sensitive to brain function and that provides an appropriate characterization of consequences of brain disease or damage for adaptive function. Thus, in observation of these patients in the community, what typically stands out are difficulties in the conceptualization of ongoing events, exercise of good judgment, ability to organize and plan with anticipation of the future. These capacities may be characterized by different terms such as Biological Intelligence, adaptive ability, executive function or the abstract attitude. It is true that neuropsychological tests often include measures of basic cognitive skills such as language or memory, but as Kurt Goldstein has pointed out that these functions are instrumentalities that support the higher functions, but do not reflect the essence of adaptive function in human society. There are certainly patients who have major deficits in these instrumentalities, such as patients with aphasia, but examination of these patients will typically reveal that they also have significant adaptive difficulties that go beyond language. Indeed, language itself has abstract and concrete aspects with the primary loss being in the conceptual use of language. In the case of traumatic brain injury, there is often prominent impairment of memory, but more extensive evaluation shows that these patients often have more fundamental difficulties in organization, planning, and conceptualization. The clever phrase has been developed by some astute observer that “a memory problem may not mean that the individual has a problem with memory.” This apparently obscure statement indicates that a patient with apparent forgetfulness may not have difficulties at the instrumentality level of formal memory, but may lack the organizational and planning abilities to learn new information.
While Reitan did not dwell on such matters in detail, his approach to assessment involving strong emphasis on complex tests of reasoning and organizational skills as well as of the individual instrumentalities reflects development of a method that, as he put it, was highly sensitive to the condition of the brain and that reflected adaptive abilities or Biological Intelligence. Thus both Ralph Reitan and Kurt Goldstein, despite several areas of disagreement, would no doubt agree as to the wisdom of using a procedure like the Category Test in the assessment of patients for brain dysfunction. There might be some quibbling about whether the Category Test, the Wisconsin Card Sorting Test or the Weigl Object Sorting Test is the best procedure—all of these tests assess common cognitive operations and have common historical roots. One important consideration is that in patients with specific syndromes, such as aphasia, Reitan felt, that we should look at more general adaptive abilities and not become preoccupied with the specifics of the aphasia. Patents with aphasia, amnesia, and other specific syndromes often typically have organizational, adaptive difficulties that transcend the specific deficit. Without denying the significance of the specific aspects of these syndromes, Reitan pointed out that the neuropsychology of the affected individual is not adequately characterized by the syndrome alone. These individuals typically have transcending organizational and conceptual difficulties that may significantly hamper adaptive function.
In retrospect, Reitan's major contribution to the development of neuropsychology can be seen as coming from three sources. (i) An appreciation of the concept of Biological Intelligence. (ii) An attitude directed toward refinement of neuropsychological interpretation through a continued search for new interpretive principles and assessment methods, and (iii) direction of an ongoing program of quantitative, experimental research utilizing well-accepted research design and statistical procedures. The first of them is, under Halstead's influence, an appreciation of the concept of Biological Intelligence with regard to the power of tests of this ability to describe the condition of the brain. While tests of this type had been available for many years, it was Halstead and Reitan who apparently first recognized their sensitivity to brain dysfunction through careful study of particular neurosurgical patients with well-documented brain pathology. These patients were carefully studied, and it was found that while some behavioral measures did not appear to be influenced by the existing neuropathology, other tests showed clear effects. Reitan apparently had a clear vision of the potential of testing of this type in studying the consequences of brain damage in a way that was readily applicable clinically.
The second source comes from Reitan's empirical orientation. This aspect of his history relates to the distinction made by some between “fixed” and “flexible” neuropsychological tests batteries. Those making this distinction characterized the Halstead-Reitan procedure as a “fixed battery.” In our view, such a distinction reflects an incomplete knowledge of history. Somehow, the view was circulated that the Halstead-Reitan Battery is nothing more than the tests used in Halstead's factor analysis published in 1947. If one looks at this factor analysis it becomes apparent that 2 or 3 of those tests are the only ones still used in the current Halstead-Reitan Battery published in Reitan and Wolfson (1993a, 1993b). The tests in Halstead's factor analysis that are still part of the Halstead-Reitan Battery are the Category Test, the Tactual Performance Test, the Speech Sounds Perception Test, and the Finger Tapping Test. However, Halstead's factor analysis also contained the Carl Hollow Square Test, a flicker fusion procedure, the Henmon Nelson intelligence test, the Time Sense Test, and a procedure called the Dynamic Visual Field Test. These tests were dropped because of failure to discriminate between patients with and without brain damage as evaluated in numerous research studies. There was also addition of new tests including the Wechsler intelligence scales, the Trail Making Test, the Seashore Rhythm Test, a modification of Finger Tapping, and sometimes the MMPI. Obviously, Reitan did not view the series of tests in Halstead's factor analysis as the only ones that should be permanently used. Throughout his career, he was continually evaluating what worked and what did not and dropped the ones that did not. Additionally, he was continually adding new tests that improved the assessment. In essence, he had a philosophy that encompassed the complementary views that if something does not work one should not persist in trying to use it, but on the other hand, “If it ain't broke don't fix it.” There is apparently no justification for characterizing the Halstead-Reitan Battery as fixed. We would note that this matter is different from the question of whether an individual clinician should give the same tests or different tests to every patient in clinical practice. This matter is a complex one involving personal preferences, practice exigencies, the nature of the referral and numerous other matters. The consideration that the clinician often has to modify the assessment approach to conduct a viable practice is not related to the question of whether the Halstead-Reitan Battery is a “fixed” or “flexible” procedure.
The third source of success is the large amount of data collected by Reitan and his colleagues. There are two databases. One is contained in the large number of publications produced by Reitan's group since the 1950s. The other is the thousands of cases preserved he has evaluated. They appear in his books and are contained in casebooks used in workshops. Reitan was both a clinician and an experimental scientist. The casebooks used for teaching purposes provide tutorials in how the Halstead-Reitan Battery is clinically interpreted. They are made more valuable by the fact that the case reports were written on a blind basis without the neuropsychologist seeing the patient or reading the case history prior to writing the report. The histories presented with the cases were added only after the report had been written. The publications are scientific reports that meet traditional publication standards including adequate sample selection and sizes, and appropriate research designs and statistical procedures. Apparently, Reitan's views prevailed regarding the use of quantitative or qualitative procedures. Most clinicians appear to want scoring systems, tests of statistical significance, and evaluation of hypotheses with state-of-the-art scientific methodology.
In this retrospective analysis, we tried to make the point that a major inspiration for Ralph Reitan's exceptionally successful career was his grasping of the significance of the concept of Biological Intelligence. He learned about it as a student of Ward Halstead who was studying the relationship between human brain function and adaptive behavior. Based upon studies of neurosurgical patients Halstead defined Biological Intelligence in terms of four factors that he called Central Integrative Field (C), Abstraction (A), Power (P), and Directional (D). There appears to be a general consensus that in its most basic characteristics the factors relate to memory (C), Abstraction (A), Attention (P), and sensory, motor and linguistic skills (D). Reitan did not use this factor analysis-based model but developed a strong interest in the contributing tests themselves. He enthusiastically accepted the view that many of these tests were indeed measures of Biological Intelligence, to a greater or lesser extent, and were particularly sensitive to alterations of brain function. Our view is that the choice of these tests for further neuropsychological investigation was an exceptionally wise one and as a battery had significant potential for becoming a highly useful research and clinical instrument. Without having been present at the time, we believe that he assembled the tests and began pruning and supplementation phases with the general aim of determining which of the tests held up as being sensitive to brain dysfunction. Thus we have the early validity study done in 1955 that clearly discriminated at highly significant levels using Halstead's tests between subjects with brain damage and matched controls, with the exception of the Flicker-Fusion and Time Sense Tests. These tests were dropped and a period of modification took place adding several new tests; namely, the Wechsler intelligence scales, the Seashore Rhythm Test and the Trail Making Test. During this period and years after, numerous studies were done with this newly revised battery including investigations of patients with varying disorders such as stroke, alcoholism and multiple sclerosis, hemisphere differences (with important involvement by the Wechsler scales) and more theoretical investigations involving such matters as aging (Reed & Reitan, 1962), quantitative vs. qualitative impairment (Reitan, 1955a, 1955b) and the role of the frontal lobes (Reitan & Wolfson, 1994). In one important chapter, Reitan provided a consideration of how inferences were made from the battery concerning the status of the four quadrants of the brain (Reitan, 1964). It should be mentioned that during this period, versions of the battery for younger and intermediate age children were being developed and are now in common use (Reitan & Wolfson, 1992, 1993a, 1993b).
In summary, “Biological Intelligence” encompasses a number of abilities that are particularly sensitive to brain function and that are those abilities required for successful adaptation to the human environment. The assessment system developed on the basis of this core concept became known as the Halstead-Reitan Neuropsychological Battery because the first version of it and the presentation of the theory was made by Ward Halstead in his 1947 “Brain and Intelligence” book. Reitan worked with this battery as Halstead's student and ultimately adopted it for use in his own research and clinical practice following several modifications. Enlisting the cooperation of neurologists, neurosurgeons and psychologist colleagues, he amassed a huge amount of data based upon the battery and extensive case documentation material obtained from the best evidence that could be obtained at the time. This exceptionally extensive system-building in which there was robust interaction between clinical assessment and research investigation has provided the field with probably the major method available for assessment of brain function.