Joseph K. Torgesen, Florida State University
Learning Disabilities Summit: Building a Foundation for the Future White Papers
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Traditionally, the term learning disabilities has been used to refer to problems acquiring academic knowledge and skills that are caused by disorders in basic psychological processes. These processing weaknesses, in turn, are caused by dysfunction of the central nervous system (U.S. Department of Education, 1977). Further, these processing weaknesses are thought to have a strictly limited impact on cognitive development; they impede the acquisition of certain academic skills while leaving many other cognitive abilities to develop normally. This conceptualization is meant to differentiate children with specific learning disabilities from those who have learning problems in school for other reasons. The idea that the processing disabilities have a relatively narrow impact on cognitive development differentiates children with specific learning disabilities from those who have the kind of general learning weaknesses associated with mental retardation. The idea that the processing limitations are intrinsic, or constitutionally based, differentiates children with learning disabilities from children whose problems learning in school are the result of lack of opportunity or motivation to learn.
The issue of concern in this paper is whether we currently have sufficient scientific knowledge to recommend that schools adopt a method of identifying children with learning disabilities that involves direct measurement of the intrinsic processing disabilities that are the presumed heart of the disorder. At present, these children are identified for special education services primarily through methods that attempt to exclude other possible explanations for the academic problem in question. By requiring children to show a discrepancy between "general learning potential" as assessed by IQ tests and performance on measures of specific academic skills, current approaches attempt to rule out explanations for learning problems associated with low general learning aptitude. Current approaches are also supposed to rule out other potential causes of the learning problem such as lack of instructional opportunities (both home- and school-based), emotional disturbance, or sensory impairment. Our current consideration of alternative approaches to classification of children with learning disabilities is motivated by widespread dissatisfaction with the IQ discrepancy approach that derives from both theoretical and empirical issues (Fletcher et al., 1998; Siegel, 1989; Stanovich, 1991).
The alternative approach to be evaluated in this paper involves direct diagnosis of learning disabilities by measurement of the intrinsic processing or capacity weaknesses that are presumed to underlie the academic performance problems shown by these children. Although the concept of intrinsic processing weaknesses is central to current definitions of learning disabilities, federal regulations specifying operational criteria for classification of children with learning disabilities do not require a demonstration of specific processing weaknesses for the diagnosis to be made (U.S. Department of Education, 1992). Assessment of intrinsic processing weaknesses was not included as part of the operational criteria for diagnosis of learning disabilities in current regulations because there has been little consensus about what these deficient processes are or how to measure them (Hammill, 1990). In the absence of agreement about the nature of the intrinsic processing weaknesses responsible for specific learning disabilities, it has become a category defined by exclusion.
During the two decades since the original regulations that outlined the operational criteria to "objectively and accurately" identify children with learning disabilities were formulated (U.S. Department of Education, 1977, p. 250), there have been enormous advances in our scientific understanding of learning disabilities. Thus, it is important to consider whether we currently have sufficient knowledge to shift away from discrepancy-based approaches that emphasize diagnosis by exclusion to direct diagnosis of learning disabilities based upon assessment of intrinsic processing weaknesses. Information relevant to this question will be organized into six sections:
When I first began my study of children with learning disabilities in the spring of 1974, the field was in a state of considerable intellectual disarray. I remember coming home from the library one evening so confused about the meaning of the word process from my reading about children with learning disabilities, that I sat down and looked it up in the dictionary. The dictionary gave two definitions and an example that helped to fix the meaning of the word in my mind. The first definition was "a natural phenomenon marked by gradual changes that lead toward a particular result," and the second was "a series of actions or operations conducing to an end" (Webster's Seventh New Collegiate Dictionary, 1965). The example provided was of the Bessemer Steel Process--a set of well specified manufacturing operations that led to the production of steel. This definition makes it clear that a process is a set of steps, operations, or developing conditions that follow one another in a certain way and that lead to, or produce, a given outcome. Of course, it is not clear that the writers of the federal definition of learning disabilities had this definition in mind when they described learning disabilities as resulting from a disorder in one or more of the basic psychological processes. However, what was very clear in 1974, and what continues to be a problem in the current literature on learning disabilities, is that the term process is used in many different ways to describe a broad variety of problems shown by children with learning disabilities. It was this confusion about the term process that led those who formulated the popular definition proposed by the National Joint Committee on Learning Disabilities (NJCLD, 1988) to delete the phrase "basic psychological processes" from their definition. This omission did not change the essential meaning of the definition, however, as the NJCLD definition still contained language about learning disorders that were intrinsic to the individual and presumed to be caused by dysfunction of the central nervous system.
One of the difficulties with the word process is that it is not tied to any particular level of explanation of human behavior. For example, a neurophysiologist might describe a problem arising from weaknesses in the processes involved in transmission of electrical impulses within neurons or across synapses, or with the transmission of information between the hemispheres of the brain. A neuropsychologist might describe primary deficits in visual-spatial-organizational processes or complex psychomotor processes. A cognitive psychologist trained within the information processing paradigm might explain a learning difficulty in terms of deficient processes operating within working memory or problems with rate of acquisition for certain types of information in long-term memory. Finally, an educator might describe a reading difficulty in terms of deficient alphabetic decoding processes or weak reading comprehension processes.
At what level of explanation are processing difficulties best described and studied in children with learning disabilities? There are three issues to be considered here. First, as one moves from descriptions at the neurophysiological level through the neuropsychological level and the cognitive level to descriptions at the educational level, the processing operations involved in the description become progressively easier to link to the actual academic performance problem that is being explained. Since, as we will see later, one of the most difficult challenges in describing academic performance problems in terms of intrinsic processing weaknesses is to be sure of the causal connection between processes and outcomes, processing descriptions that are as close as possible to the academic problem being explained have some inherent advantages. On the other hand, the higher one goes in the explanatory hierarchy (from neurophysiological to educational), the more difficult it is to be sure the processing differences used in the explanation are intrinsic, or constitutionally based, rather than learned through varying experiences. Finally, the measurement technology and expertise required to identify processing weaknesses also varies with the level of explanation. Assessment of processes occurring at the neuronal level requires highly specialized equipment and considerable technical training, while assessment of processing differences at the educational level require less technology.
Since one purpose of this paper is to consider whether it is practical, at this point in time, to recommend that the public school system in the United States classify children as learning disabled by identifying those with intrinsic processing weaknesses, measurement considerations are of obvious importance. It is also clear that the level of explanation we choose should be below the educational level, as that is simply a description of the learning outcome. For example, when genetic influences on variability in reading skill are discussed, no one seriously entertains the idea that there is a specific gene, or combination of genes, for reading per se. Similarly, few would agree that it is adequate to explain the problem by indicating the child has a disability in "the reading process." Rather, the most common current explanations of genetic influences on reading growth are that they directly affect the phonological component of natural language ability (Olson, 1999). That is, specific weaknesses in the ability to process phonological information are offered as an explanation for the reading difficulty, and phonological processing disabilities are conceptualized as intrinsic or constitutionally based limitations that are significantly heritable.
To provide additional context for considering which level of explanation is most viable for diagnostic and classification purposes, consider the levels of explanation required for complete understanding of any particular of learning disability (Torgesen, 1999). This discussion starts with the recognition that children can have learning problems in school for many reasons, and that the definition of learning disabilities is meant to focus our attention on one particular type of learning problem. Thus, a theory of learning disability must be consistent with the major elements of current definitions. The first step in the development of a coherent theory of learning disabilities is to specify the learning or performance problem that is to be explained by the theory. There cannot be a single coherent theory of learning disabilities because the term learning disabilities refers to a heterogeneous set of learning problems. It is not reasonable, for example, to expect the same theory to explain both difficulties acquiring word reading skills and difficulties with listening comprehension. Thus, the starting point for any coherent theory of learning disabilities must be a precise and focused description of the specific academic problem to be explained.
The first level of explanation in a coherent theory of any type of learning disability should be a description of the basic psychological processes that are the proximal cause of the academic learning problem. This is the first level at which we might reasonably begin to attach the word intrinsic. It is meant to identify the fundamental information processing limitations that cause the child to have difficulty acquiring specific academic skills. It is at this level of explanation that we have made enormous advances in the last 20 years. These advances have occurred not only in understanding the basic processes that underlie development, but also in identifying those processing limitations that produce individual differences in learning outcomes for children exposed to the same learning opportunities. The reason for these advances is that the information processing paradigm, as a way of studying and explaining human behavior, has matured during this time, and it has contributed important methodologies and theoretical constructs to the understanding of human learning and behavior.
The information processing approach is of fairly recent origin (Massaro, 1975), and was developed in the aftermath of successful simulation of human cognitive achievements (i.e., chess playing, numerical calculations) by computers. The availability of clear descriptions of the different processes by which computers solve human-like intellectual problems led researchers to the hope that similar descriptions of internal psychological events intervening between receipt of a stimulus and emission of a response might also be developed for humans. Thus, information processing accounts treat mental processes in terms of different operations that are performed on information. John Flavell, an eminent cognitive developmental psychologist, explained the paradigm this way:
Like a computer, the (human) system manipulates or processes information coming in from the environment or already stored within the system. It processes the information in a variety of ways: encoding, recoding, or decoding it; comparing or combining it with other information; storing it in memory or retrieving it from memory; bringing it into or out of focal attention or conscious awareness, and so on...the ideal goal of the information-processing approach is to achieve a model of cognitive processing in real time that is so precisely specified, explicit, and detailed that it can actually be run successfully as a working program on a computer. (Flavell, Miller, & Miller, 1993, pp. 8-9).
From the point of view of information processing theory, processes are defined as sequences of mental actions or operations that transform and manipulate information between the time it enters as a stimulus and the time a response to it is selected and executed. Although, as we shall see, some information processing skills or capacities are clearly acquired through learning and experience, others may represent basic features of the biological "hardware" that would qualify as intrinsic or constitutionally-based features of an individual child's cognitive capabilities.
Once a theory of learning disabilities has identified the deficient psychological processing operations that are the proximal cause of the poor learning outcome, the next level of explanation must involve identification of the locus of neurological impairment that is a likely cause of the limitation in processing capacity. Again, this is a requirement of any theory that is consistent with current definitions. The locus of neurological impairment might be either structural (e.g., a difference in distribution, organization, or density of neurons, or presence of anomalous formations) or functional. If a functional limitation is identified, it might use concepts from neurophysiology, and when fully understood, would probably be described as a deficient neurophysiological process. One advantage of having a precise description of processing deficiencies at the psychological level is that it can provide guidance about where to look for impairments in the central nervous system. For example, the strong evidence that one common form of reading disabilities is caused by weaknesses in phonological processing ability has directed attention to the left temporal region of the brain, which is identified with speech processing, as a possible locus of central nervous system dysfunction in children with reading disabilities. Conversely, if no structural or functional anomalies are found in these areas, this should lead to additional theory development at the psychological level.
The last level of explanation required by a complete theory of learning disabilities involves specification of the etiology of the structural or functional impairment in the central nervous system causing the disability. Like the word process, the meaning of the word constitutional is not well specified in current definitions of learning disabilities. Use of the term in the context of other elements of the definition (e.g., they are not the result of extrinsic conditions such as cultural differences or lack of opportunities to learn) would suggest that it means something similar to inherent; it is a biologically based disability that is present when the child is born. The prototypical cause for this kind of disability would be genetic. That is, a child's genes would either lead to the development of information processing weaknesses present at birth or would influence the emergence of processing weaknesses arising during development. However, there are clearly other causal possibilities for intrinsic, constitutionally based processing weaknesses arising from dysfunction or damage to the central nervous system (Rourke, 1989). It is also possible for children to bring "intrinsic" processing disabilities with them to school that arise as a result of environmental conditions following birth (Hallahan, Kauffman, & Lloyd, 1996).
This extended excursion into learning disabilities theory is offered in support of the idea that processing disabilities conceptualized at the psychological level are potentially most useful for widespread identification and classification purposes. As we will see shortly, there is clear evidence for intrinsic psychological processing capabilities that are given as part of our genetic or biological make-up and that are also accessible to assessment outside the medical or biological laboratory. Thus, for the remainder of this paper, the focus will be to determine whether we currently have enough scientific knowledge to begin classifying children as learning disabled by direct assessment of the psychological processing weaknesses responsible for their observed learning difficulties. I will begin by making some important distinctions among different types of psychological processes.
Funding for NRCLD is provided by the U.S. Department of Education, Office of Special
Education Programs. Award No. H324U010004. Opinions expressed herein are those of the National
Research Center on Learning Disabilities and do not necessarily represent the position of the U.S.
Department of Education.
© 2007 National Research Center on Learning Disabilities
Last Updated: November 19, 2007
Contact: nrcld@ku.edu