On the role of group studies in neuropsychological and pathopsychological research

Abstract

It is argued that group studies are legitimate in pathological populations. Exceptions to statistically reliable group effects must be explained, but have no more significance for theory construction than similar exceptions in studies of normals. A distinction must be made between consistent and inconsistent exceptions; the former are more seriously damaging to the assertion of a universal cognitive system underlying performance on an experimental task. Because exceptional cases may at least be examined for other deficits in pathological but not normal populations, the task of exploring consistent minority performance is, in principle, easier in the pathological than in the normal case. The main use of group data in developing theories of normal cognition and theories of the neural basis for cognition is the documentation of associations of deficits, since such co-occurrences imply common factors underlying both abnormal performances. This use of group data is particularly crucial when one “deficit” is an organic lesion, since other approaches to determining the relationship between deficits which are available when both deficits are functional are not available in this particular circumstance.