Joseph K. Torgesen, Florida State University
Learning Disabilities Summit: Building a Foundation for the Future White Papers
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One important distinction among psychological processing operations is that between processing sequences or capabilities that appear to function automatically as part of the biological "hardware" of the brain and those that are assembled as an adaptive response to the requirements of specific tasks. When humans enter the world, they are immediately capable of complex information processing activities in a number of domains. For example, newborn infants can perform the complex mental calculations required to localize sounds without seeing the sound source (Morrongiello, Fenwick, Hillier, & Chance, 1994; Wertheimer, 1961). The brain also seems "wired" to perceive phonemic contrasts categorically, which is of enormous assistance in acquiring receptive speech capabilities (Aslin, Jusczyk, & Pisoni, 1998; Eimas, Siqueland, Jusczyk, & Vigorito, 1971). Human beings also appear to process information about the frequency of events automatically, without really thinking about it or even intending to do it, and children as young as 5 years old are as effective as college students in retaining this kind of information (Hasher & Zacks, 1984).
One of the central themes of developmental psychology over the past 20 years is the increasing recognition that human beings are capable of much more behavioral complexity and complex information processing at very young ages than was previously thought. As Fischer and Bidell (1991) suggest:
The behavioral abilities with which human beings are genetically endowed are far richer and more complex than traditional accounts of cognitive development imply. New research seems to have revealed rich sets of perceptual and cognitive abilities in infants and young children. ... these early abilities show the starting points from which cognitive development must emerge. As starting points, they set limits or constraints on what is possible and thereby help to channel the direction of development. (p. 200)
Flavell and his colleagues (Flavell et al., 1993) go on to point out that:
We seem to be biologically prepared to do very specific kinds of information processing and very specific kinds of learning, with no apparent links between one set of processing mechanisms (e.g., those for discriminating speech sounds) and another (e.g., those for extracting numerical information). Different theorists talk about these highly specialized capacities in different ways... Common to the various conceptions, however, is an emphasis on domain specificity--these are processes that perform very specific tasks, not all-purpose learning mechanisms. (p. 336-353)
As suggested in the comments by Flavell and his colleagues, processes can be domain-specific or they can be domain-general. A good example of a domain-general learning process that is present from birth is the ability to form representations of objects or events so they can be recognized as familiar (Werner & Siqueland, 1978). The rate at which children can learn to recognize objects as familiar predicts their later general intelligence quite accurately (Rose, Feldman, & Wallace, 1992). This recognition capability is a domain-general process and thus exerts a relatively broad influence on cognitive development: Infants who are slow to habituate to an item on repeated presentation show slower rates of general cognitive development, resulting in lower measured intelligence at later points in development. Domain-general processes or capacities are not a good place to look for explanations of specific learning disabilities, because their effect on learning and performance is so pervasive. If a child is deficient in an important domain-general information processing skill, the likely result will be mild to serious mental retardation rather than development of a specific learning disability.
A third important distinction among different kinds of information processing activities is between automatic and controlled processes. Processes that require significant amounts of attention and conscious direction are labeled controlled, while those that require little, if any attention, are labeled automatic. Activities that are initially accomplished through controlled processing activities can eventually be accomplished via automatic processes as the brain establishes highly practiced information processing routines. A clear example of this change from controlled to automatic information processing occurs during the acquisition of reading skills. Whereas the first time a word is encountered in print it must be identified using a combination of controlled processes involving phonemic analysis and contextual constraints (Share & Stanovich, 1995), after the word has been read accurately several times, the brain forms a representation of its spelling that allows it to be recognized instantly and automatically, with almost no attention or effort involved (Ehri, 1998). This transition from controlled to automatic processes is important in development, because when automatic processes are employed, mental resources are freed to accomplish other tasks. In the case of reading, when word recognition occurs automatically, processing resources are freed to construct the meaning of the passage.
The distinction between automatic and controlled processes is important for the present discussion because it has important implications for assessment of processes and capacities in children with learning disabilities. For example, one of the strongest themes in developmental psychology over the past 20 years is that older children are more adaptive and efficient in the use of controlled information processing strategies to accomplish both novel and routine tasks (Siegler, 1998). Frequently, when older children perform better than younger children on a learning or memory task, it is not because the older child has greater learning or memory capacity per se, but because older children more successfully use the processing resources they have to adapt to the requirements of the task.
Another factor that affects measurement of basic psychological processes is that automatic processes can become more efficient with experience. For example, as children acquire more familiarity, or exposure, to different types of information, their processing of it becomes more and more efficient. Thus, one important explanation for the significant difference between younger and older children in their ability to remember sequences of numbers involves older children's greater familiarity with numbers: They process the numbers more automatically, and thus their apparent capacity for remembering them increases (Case, Kurland, and Goldberg, 1982). In this case, what might initially be interpreted as a difference in memory capacity between older and young children can be directly explained in terms of the older child's more automatic processing of the stimuli to be remembered. Siegler's (1998) discussion of differences between older and young children's processing experience, and its relationship to their apparent processing capacities, provides a cautionary note about the potential difficulties involved in directly assessing intrinsic processing or capacity limitations in children with learning disabilities:
Developmental improvements in performance can be produced either by an increase in the child's resources or by a decrease in the resources the child expends in doing the task. How might the resources required to do a task decrease with development? The older children know more about numbers. This greater familiarity could help them remember the numbers more efficiently. They also know more strategies, such as rehearsal, for enhancing their recall. They also are more skillful in choosing when to use the strategies they know. Thus it is clear that older children can store more material in working memory, but it remains unknown (and perhaps unknowable) whether this is because of a change in the actual capacity of working memory or because of changes in knowledge and strategies that allow more material to be stored within the same capacity. (p. 189).
Processing differences among children can affect learning and performance in a number of ways. For example, children can be different from one another in accuracy of processing for specific types of information. A good example of this type of processing difficulty is provided in the work of Paula Tallal and her colleagues (Tallal, 1980; Tallal, Stark, & Mellits, 1985). They have developed a theory to explain language disabilities by suggesting that some children have special difficulties processing rapidly changing or rapidly sequential auditory stimuli. This difficulty arises because these children's brains do not sample acoustic signals sufficiently rapidly to note changes of short temporal duration. Thus, the children perceive some speech contrasts, or other rapid temporal events, inaccurately.
Children's performance on a variety of tasks can also be affected by differences in processing speed. Wolf and Bowers (1999) have developed a hypothesis to explain certain kinds of reading difficulties in terms of limitations in visual processing speed for letters. They hypothesize that "slow letter (or digit) naming speed may signal disruption of the automatic processes which support induction of orthographic patterns, which, in turn, result in quick word recognition" (Bowers & Wolf, 1993), p. 70). According to this explanation, if children are sufficiently slow at visual recognition of letters, it interferes with their ability to construct a mental representation of a word's spelling that will allow the word to be recognized automatically.
Children can also be different from one another in processing capacity, and this would certainly produce individual differences in performance on tasks that place demands on this capacity. Lee Swanson and his colleagues have conducted an extensive series of studies from which they propose that children with both reading and math disabilities suffer from a domain-general capacity limitation in working memory (Swanson & Ashbaker, 2000). This hypothesis will be discussed more completely in the next section.
Finally, differences in learning or performance can also result from children's use of inefficient processing sequences, or weaknesses in the coordination of processing components.
It is by now widely acknowledged that a reliable characteristic of many learning disabled children is that they frequently appear disorganized on tasks and often do not use efficient strategies to solve problems or acquire new information (Denckla, 1994; Meltzer, 1993). However, whether these problems in organization and strategy execution qualify as intrinsic processing limitations and primary causes of learning disabilities or whether they are a secondary characteristic arising as a reaction to early and chronic academic failure is a question that is not completely resolved (Kistner & Torgesen, 1987; Meltzer, 1993). One problem with strategy-based explanations of processing weaknesses in children with learning disabilities is that strategic, or controlled, processes are highly susceptible to modification through experience, motivation, and opportunities to learn (Siegler, 1998). In studying these kinds of processes, the researcher has an especially heavy burden to show that weaknesses in their execution and organization have a biological rather than an experiential basis.
A major conclusion of this section is that the most productive level to search for intrinsic processing weaknesses in children with learning disabilities is the psychological or neuropsychological level. At this level of explanation, it is possible to identify processing capacities and skills that can be conceptually linked to the biological substrate (and would thus qualify as intrinsic to the child), but which are also potentially measurable outside a medical or biological laboratory. At this level, processes are defined as sequences of specific mental actions that transform and manipulate information between the time it enters as a stimulus and the time a response to it is selected and executed. It is important to note that these processes, or processing descriptions of behavior, are theoretical constructs. There is no claim that they are a veridical representation of specific neurological events. Rather, these processing descriptions are offered to help understand reliable patterns of human cognitive functioning, and they are an intermediate level of explanation between overt behavioral outcomes (e.g., extreme difficulties acquiring automatic recall of math facts or difficulties acquiring use of phonemic decoding skills in reading) and their biological underpinnings.
There is good evidence that humans are born with biological hardware capable of supporting complex information processing routines. Since they are present from birth, these biologically based processing capabilities are part of the child's constitutionally based information processing capability and are thus subject to the same kind of variability in speed, accuracy, or capacity as other biological endowments. It is processing capabilities that arise relatively early in development, that are domain-specific, and that are relatively automatic in execution and operation that are the most likely candidates for the kind of intrinsic processing weaknesses that are referred to in definitions of learning disabilities.
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