Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Psychology

Faculty/School

Faculty of Science

First Advisor

Alexandra Gottardo

Advisor Role

Thesis Supervisor

Second Advisor

Todd Ferretti

Advisor Role

Thesis Supervisor

Abstract

Event-related brain potentials (ERPs) were recorded from 20 children with dyslexia and controls matched on age, sex, nonverbal reasoning, and handedness (ages 8-12 years) as they listened to and read sentences that varied in syntactic complexity and the working memory load they induced [subject-subject (SS) and subject-object (SO) relative clause sentences]. In each modality, control children demonstrated amplitude differences between the brainwave potentials elicited to each sentence type. When listening, controls, and children with dyslexia did not differ in the N400 effect elicited in response to the relative verb of SO sentences, thus indicating auditory sentential processing occurred in a similar manner for both groups of children early in the sentences. However, by the later main verb region of SO sentences, thematic role assignment, as indexed by the left anterior negativity (LAN), was absent in children with dyslexia, suggested that rather than syntactic complexity, overtaxed working memory inhibited dyslexics’s ability to assign thematic roles. When reading, the N400 effect was again demonstrated by each group at the relative clause of SO sentences; however children with dyslexia exhibited a latency delay in comparison to control children. Similar to auditory processing at the main verb, while reading only the control goup demonstrated LAN effects in response to SO sentence structure. In order to investigate working memory capacity in more temporal detail, slow cortical potentials were measured over the full duration of the sentence. Results demonstrated that while both groups were able to utilize phonological working memory to store sentential information when listening to sentences, only controls could reliably do so when reading. The data indicates that the syntactic deficits inherent in dyslexia are mediated by phonological working memory. These results support the phonological limitation hypothesis posited by Shankweiler et al. (1992), which contends that all impediments related to dyslexia are mediated by a primary deficit in phonological processing.

Convocation Year

2007

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