Efficacy of a psycholinguistic treatment of dyslexia
In this chapter, the results of a research project into the efficacy of a Dutch psycholinguistic treatment of dyslexia are presented. It is a computer-based treatment program, which presents dyslexic participants with a learning system that clarifies the basic linguistic elements and operations by which one’s writing system encodes the characteristics of the spoken language system. Basically, it focuses on learning the dyslexic pupils to recognize and use the phonological and morphological structure of words.
The theoretical foundations of this treatment are discussed first. Next, the results are presented of a series of experiments, which provide insight in both the external and internal validity of the treatment. Concerning its external validity, clinical significant effects of treatment on general reading and spelling skills are reported. At the end of treatment, participants attained an average level of reading accuracy and spelling. The attained level of reading rate was comparable to the lower bound of the normal range. These effects appeared to be independent of age, social-economic status, and IQ. Phonological encoding capacities had an impact on treatment duration, but not on the overall effect of the treatment. In addition, a 4-years follow-up study revealed that the effects of treatment were long-lasting.
In view of the internal validity, a process-oriented evaluation was conducted to provide a detailed window on the dynamics of change by examining the relation between the timing of treatment effects and the presentation order of treatment components. The study revealed that the time course of treatment effects accurately matched the predicted temporal ordering. The children showed a cascade of improvements that corresponded to the presentation order of the treatment components. In addition, a study was conducted to elucidate the dynamics of change in the accuracy and rate of reading. It was revealed that, in concordance with production models of skill acquisition, the treatment method first resulted in a more prominent development of reading accuracy, which appeared to reflect the accurate formation of the system of essential elements and operations underlying the skill of reading. Subsequently, it resulted in a more prominent development of reading rate, which is assumed to reflect the optimization of the execution of this system.
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