Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 12 table of contents.
Learning disorders come in many varieties. If a specific type of information processing deficit can be isolated as the cause of a disorder, then highly targeted therapies can sometimes help a person develop skills previously lacking. For example, one subset of learning disordered children has a specific problem with rapid language sounds. Often they cannot distinguish between the sounds Da and Ga. If you say those two syllables and listen to the difference, you can appreciate that it is very subtle. The d sound in Da comes from contact between the tongue and the front of the roof of the mouth; the g sound in Ga comes from contact between the tongue and the back of the roof of the mouth. Some children cannot seem to hear the difference, which leads to problems speaking and reading.
What is an example of a specific learning disorder involving language sounds?
Kraus, McGee, Carrell, Zecker, Nicol, and Koch (1996) showed that the brains of children with this disorder did not discriminate between the sounds. To show this, they looked for a special brain wave (EEG) event called the MMN (mismatch negativity). This is a small but easily detected change in brain waves which occurs when a series of similar stimuli are followed by a different stimulus. It is robust (occurs in everybody, in a wide variety of circumstances) and it does not require learning, attention, or even normal consciousness (it can be detected in newborns and people who are asleep).
What is the MMN and how did researchers use it to analyze a learning disorder? What did the results show?
To measure the MMN events, the researched put scalp electrodes on children who were either normal or learning disabled (LD). The children watched TV while wearing headphones. The headphones let them hear the audio track of the TV show, but in the background, a voice softly pronounced a series of syllables. The series of syllables might be: da-da-da-da-da-da-da-da-da-da-ga-da-da-da. The researchers watched to see if the different syllable (ga) was accompanied by an MMN event. The children paid attention to the soundtrack of the TV program and did not consciously pay attention to the syllables. The results were clear: normal children showed an MMN response, learning-disabled children did not. This showed that the problem existed very early in the nervous system, in the part of the brain that analyzes sounds before they enter consciousness.
How was the language sound learning disorder successfully treated?
Children with this disorder were successfully treated using a videogame-like adaptive training exercise. It was called adaptive because it adjusted to their abilities. First the children heard slowed-down recordings of speech, and they had to detect the difference between "da" and "ga." At a slow speed, the difference was easy to hear. Then the speech was gradually speeded up, while the children kept trying to hear the difference. Using this game which focused specifically on the rapid speech sounds they had trouble perceiving, children were able to overcome their deficit in this type of information processing. Soon they could hear the differences at normal speed, just as well as other children.
What does this study indicate, according to the researchers?
Does this mean the children had a built-in brain problem? Just the opposite. The researchers noted, "These studies...strongly indicate that there may be no fundamental defect in the learning machinery of most of these children, because they so rapidly learn the same skills at which they have been defined to be deficient." For one reason or another, these children had not picked up on these particular language sounds, which occur very quickly (in about 10 milliseconds). Once they were trained specifically to hear the distinction, they picked it up quickly (Merzenich, Jenkins, Johnston, Schreiner, Miller, & Tallal, 1996).
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