The Neuropsychology of Learning Disabilities
An evaluation that centers solely on the simple process of subtracting, or regressing, IQ from achievement is a narrow procedure that misses much of the difficulties frequently seen in these children. The ability to process information is a very complex and distributed operation. Skills that are necessary to understand to evaluate the child's learning skills include the ability to process language, to understand what he/she hears, to organize information, the speed information is processed, attention, the child's ability to hold information in mind while solving a problem, and the ability to self-monitor the reading process.
Language difficulties have frequently accompanied problems in learning to read. These language problems may be in receptive and/or expressive language. The phonology of the language can be tricky to master. Language is a natural process of our brain and there are structures devoted to its development. Reading, however, is an acquired skill and children must be directly taught how to do this task. When a child has a language problem in addition to reading deficits, the progress is much more difficult. Approximately 70 to 80 percent of children learn phonological coding skills without difficulty. The remaining 20 percent show differing levels of success and, based on previous studies, the determining aspect may be the intervention provided as well as the child's overall verbal skills.
The ability to decode words is a fairly well-known area of difficulty for children with learning disabilities--however, more recent research indicates the main difficulty is not just the decoding of the word but also the rate of decoding (Joshi, 1999; Woodcock, 1991). Speed of information processing has been found to separate fluent from nonfluent readers (Semrud-Clikeman et al., 2000). Children with reading disabilities were found to be slower at naming words and nonwords as well as with naming letters and numbers (Aaron et al., 1999).
An important aspect for reading is comprehension. Listening comprehension is mediated by the same cognitive processes as reading comprehension only through a different modality (Joshi, 1999). Assessing the ability to process information without the confound of decoding allows one to more fully evaluate the child's ability to understand and process language and to determine whether the difficulty lies with decoding or comprehension. An evaluation of these skills is necessary to understand where the breakdown in skills lies and thus, to develop the most appropriate intervention.
An additional neuropsychological process that is important to reading skills development is working memory. Working memory is the ability to hold information in mind while solving a problem, remembering a phone number, or decoding a word. Adele Diamond studied working memory in young children. The child observed her hiding an object and then was asked a few seconds later, where the object was. Children younger than one could not find the object and used the rule of "Out of sight, out of mind." Before age one the frontal lobes are unable to process delayed information. However, as the child grows, he/she becomes more able to retain information for a short amount of time while processing information. In order to decode words, one's working memory must be functional and allow the child to retain a "template" of the letters until the word is sounded out. If there is a breakdown in the ability to hold this information in mind or if the time required recalling the sound-symbol relationship is prolonged the child will experience difficulty reading (Semrud-Clikeman et al., 2000). Working memory is a crucial skill for early reading recognition and later reading comprehension and needs to be assessed in order to develop the most appropriate method of intervention.
Working memory has also been linked to the ability to organize a task's temporal aspect. Not only is input encoded, it is also tagged to a time when the task was learned (Gazzaniga, Ivry, & Magnum, 2002). The prefrontal cortex is linked to memory systems that allow the child access to previously learned materials. If difficulty is present at the outset, or the working memory stage, the child will have difficulty recalling previously learned skills (i.e., the letter c in c-a-t has a certain sound) and thus decoding will be slower and effortful. Similar difficulty arises in spelling and in learning mathematics. For example, in mathematics the child needs to remember certain mathematics facts as well as when to utilize what procedure.
Executive functions are another skill that is important for the learning process. Executive functions are those skills that apply to the "how" something is accomplished rather than just the "what." These skills are also important in helping a child evaluate his/her performance. They also allow us to inhibit responding to irrelevant stimuli. The selection of what is important to encode is an important ability in learning to read, write, and do mathematics. In addition, a child needs to learn to listen to what he/she is reading (either orally or silently) and evaluate its correctness. This skill becomes more important in older grades as the child needs to be able to self-correct mistakes. The awareness of "how I'm doing" is crucial to the learning process and allows the child to change behaviors or to take corrective action as necessary. These skills do not come into full fruition until early adulthood and some would suggest not until one is 32 years of age do we have a fully mature brain (Denckla, 2003). Thus, an important issue to assessment would be to evaluate the child's ability to understand his/her thinking processes.
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