Neuropsychological and psychosocial subtyping: A review of investigations within the University of Windsor laboratory.

Donald O. Hebb Award for Distinguished Contributions to Psychology as a Science (1999) -- Prix Donald O. Hebb pour contributions remarquables a la psychologie en tant que science (1999)AbstractSubtyping studies that have addressed a variety of theoretical and clinical issues are reviewed. The syndrome of Nonverbal Learning Disabilities, especially with respect to its manifestations in many forms of pediatric neurological disease, disorder, and dysfunction, is emphasized. It is concluded that the establishment of reliable and valid subtypes holds considerable promise for contributions to model-building as well as providing avenues to clinical relevance.In this paper, a brief outline of our program of research is reviewed from a particular vantage point, viz., the relevance of establishing subgroups and subtypes for the testing of important hypotheses and model- building in developmental and clinical neuropsychology. The nomothetic versus idiosyncratic controversy, especially as it applies to the neuropsychology of learning disabilities (LD), is addressed first. This is followed by a description of the subtyping enterprise and its role as a kind of "middle ground" between these two extremes. Then, a summary of the results that we and others have generated using this methodology is framed in a series of research questions. Also, a brief description of one subtype, the syndrome of Nonverbal Learning Disabilities (NLD) is outlined, together with an examination of the incidence and relevance of this syndrome for various types of neurological disease, disorder, and dysfunction.LD AS AN HOMOGENEOUS ENTITYThere is an important similarity between the history of the neuropsychological study of LD in children and the investigation of frankly brain-damaged individuals. This similarity lies in the fact that most early investigators in both of these areas of scientific endeavour ascribed to a particular viewpoint -- one that managed to hold sway for a protracted period of time during the development of these fields. This viewpoint held that impaired individuals (be they learning-disabled or brain-damaged) have very much in common with others who are so afflicted. Thus, investigators who ascribed to this position felt comfortable in maintaining, either explicitly or implicitly, that there was such a unitary entity as the "brain-damaged child" or the "learning-disabled child. " In turn, they felt that significant advances in our understanding of the neuropsychological dimensions of these disorders would accrue from studies that involved comparisons of children suffering from either of these two types of disorder with appropriately matched control (i.e., normal) children on carefully selected variables of theoretical interest.As can be gleaned from any systematic review of the learning- disabilities literature prior to the late 1970s (e.g., Benton, 1975; Rourke, 1978a), this "comparative populations" (Applebee, 1971) or "contrasting groups" investigative strategy was the almost exclusive approach adopted by North American and European researchers. Studies involving comparisons of groups of youngsters with LD with groups of age-and otherwise-matched "normal" controls were employed to determine the deficit(s) that characterize the neuropsychological ability structure of the child with LD (Doehring, 1978). The use of this method for the determination of the neuropsychological abilities and deficits of children with LD assumed, implicitly or explicitly, that such children formed an univocal, homogenous diagnostic entity.This approach was also characterized by rather narrow samplings of areas of human performance that were thought to be related to the learning (primarily reading) disability. For example, some researchers who were convinced that a deficiency in memory formed the basis for LD in youngsters would follow a rather straightforward research tack: for example, they would measure and compare "memory" in groups of children with LD and matched control children. …