INTRODUCTION AND OVERVIEW
Some of the issues that dominated, or at least held sway, in the neuropsychology of learning disabilities (LD) in the 1970s included: the definition of LD, whether there are reliable and valid subtypes of LD, whether and to what extent LD are related to cerebral dysfunction, and whether LD are related to types and/or degrees of psychosocial dysfunction (Rourke, 1975). It is clear that these issues are not mutually exclusive. Indeed, they are intimately connected. We have made progress in examining these issues, but future challenges will be substantial.
Definitions: General and Subtypal
It has become clear that so-called "discrepancy" definitions of LD lack scientific credibility (Fletcher et al., 1989; Fletcher, Francis, Rourke, Shaywitz, & Shaywitz, 1992). One alternative is strictly neuropsychological definitions that my colleagues and I have proposed (e.g., Rourke, van der Vlugt, & Rourke, 2002).
The following are our general definition and some elements of our specific subtypal definitions of LD. The definitions arise from the part of our research program during the last 40 years that has focused on delineating reliable and valid subtypes of LD. (For reviews of this work and the development of these definitions, see Rourke, 1985, 1987, 1988a, 1988b, 1989, 1991, 1993, 1995a, 1995b, 2000; Rourke & Conway, 1997; Rourke & Fuerst, 1992; Rourke et al., 2002.)
General definition. LD are specific patterns (subtypes) of neuropsychological assets and deficits that eventuate in specific patterns of formal (e.g., academic) and informal (e.g., social) learning assets and deficits. LD may also lead to specific patterns of psychosocial functioning. These generalizations must be construed and evaluated within the context of particular historical and sociocultural contexts.
Specific subtypal definitions. Of particular interest are two subtypes of LD that we have identified in a reliable and valid manner: nonverbal learning disabilities (NLD) and basic phonological processing disabilities (BPPD).
The NLD subtype (syndrome) is characterized by a specific pattern of relative assets and deficits in academic (well-developed single-word reading and spelling relative to mechanical arithmetic) and social (e.g., more efficient use of verbal than nonverbal information in social situations) learning, as well as specific, developmentally dependent patterns of psychosocial functioning. Generally, in children with NLD below the age of 4, psychosocial functioning is relatively typical or reflective of mild deficits. Following this period, emerging manifestations of externalized psychopathology are frequent; the child may be characterized as "hyperactive" and "inattentive." The usual course with respect to activity level is one of perceived "hyperactivity" followed by evident normoactivity and then hypoactivity with advancing years. By older childhood and early adolescence, the typical pattern of psychopathology is of the internalized variety, characterized by withdrawal, anxiety, depression, atypical behaviors, and social skill deficits.
The BPPD subtype is characterized by a specific pattern of relative assets and deficits in academic (i.e., poorly developed single-word reading and spelling relative to mechanical arithmetic) and social (e.g., more efficient use of nonverbal than verbal information in social situations) learning. The neuropsychological profile and outcomes of this subtype of LD stand in marked contrast to those of NLD. For example, the misspellings of individuals who exhibit NLD are almost always phonetically accurate (Sweeney & Rourke, 1978), whereas the misspellings of persons with BPPD are most often phonetically inaccurate. Also, the neuropsychological assets and deficits of the BPPD subtype do not necessarily lead to any particular configuration of difficulties in psychosocial/adaptive behavior.
For a more extensive description of the neuropsychological assets and deficits (definitions) of NLD, the interested reader is referred to Rourke (1989). …