Disentangling Dyslexia: Phonological and Processing Impairment in Developmental Dyslexia

Aim of this work is to analyze thoroughly the most peculiar aspects of Developmental Dyslexia, focusing on its distribution and, especially, on its manifestations and possible causes, and to propose an original hypothesis able to account for the cognitive impairment underlying this disorder. It has been demonstrated in fact that dyslexia is not just an impairment preventing children from learning to read and spell properly, but that it is a more complex and articulated syndrome. Beyond the well-known reading and spelling difficulties, dyslexic individuals exhibit marked phonological disorders, vocabulary deficits and poor lexical retrieval, and problems in the comprehension of complex grammatical structures which involve high processing costs to be interpreted. Moreover, dyslexia is often associated to attention deficits arising in particular when the subject is required to focus on relevant stimuli filtering out those that are irrelevant and distracting. After a deep discussion of these aspects, the author analyzes the main theories developed through the decades to account for dyslexia, proposing then an original hypothesis able to account for all the manifestations associated to the disorder, the Phonological and Executive Working Memory Deficit Hypothesis. The results of an original experimental protocol reported in the book demonstrate that dyslexics suffer from a limitation affecting their Working Memory and hampering in particular their phonological memory and their executive functions. As a consequence, this impairment disrupts their phonological competence, resulting in poor reading and spelling skills, slows down their vocabulary development, and hampers their performance in complex tasks which are particularly demanding in terms of Working Memory resources. Three experimental protocols reviewed in the book have been developed to test this hypothesis, analyzing the comprehension of complex structures such as the interpretation of scalar implicatures, negative sentence and pronominal expressions. Consistently with the hypothesis presented in this work, results confirm that dyslexic children have significant difficulties in comparison to age-matched and even younger controls, suggesting that their poorly functioning phonological memory and executive functions hamper their performance in tasks requiring a good phonological competence and demanding a high amount of cognitive resources.