Welcoming a paradigm shift in neuropsychology

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In order to understand the relationships between brain structure and function, we need to appreciate both the biological and non-biological variables which can influence behavioural data. We do not dispute that mild brain injuries cannot, in principle, have lasting neuropsychological effects. We merely assert that, as injury severity becomes increasingly mild, the role of non-organic factors affecting performance increases commensurately. Among these factors is the phenomenon of incomplete effort. In the past decade, this topic has become a key focus in applied neuropsychological research. In our critique, we pointed out that Dr. Bigler has not addressed this phenomenon, although it is one that we cannot escape. It is now widely recognized that, if a patient does not put forth a full effort during testing, neuropsychological test scores will underestimate the person’s true capabilities. Whether in the single clinical case or in group studies, if such contaminated data go unrecognized and are incorrectly regarded as being valid, we will draw false conclusions. In the case of patients with mild head injuries, poor effort on testing not only has some effect on neuropsychological test scores but it can easily override the effects of most other variables. Poor effort creates the illusion that people with mild head injuries have suffered far more severe neuropsychological impairment than patients with well established severe brain injuries or brain tumors. Accordingly, the title of the paper by Green, Rohling, Lees-Haley, and Allen (2001) was “Effort has a greater effect on test scores than severe brain injury in compensation claimants.” In this study, patients with mild head injuries performed on many neuropsychological tests at a level very close to the normal mean established by independent normative studies. This finding applied to those who passed effort testing with the Word Memory Test (Green, Allen, & Astner, 1996; Green & Astner, 1995; Green, Lees-Haley, & Allen, 2002). However, the group of mild head injury patients, who failed effort testing, showed a severe suppression of neuropsychological test scores. Their overall performance was, on average, 1.4 standard deviations below the normal mean. In contrast, the patients with the most severe brain injuries scored only 0.4 standard deviations below the normal mean. It is very difficult to develop a biological explanation for these findings. The Word Memory Test effort subtests are so simple that even mentally retarded children or children with fetal alcohol syndrome can easily score almost 100% correct but adult patients with mild head injuries scored lower on the effort subtests than these children ( Green & Flaro,