Developmental dyslexia is a specific difficulty in acquiring literacy skills that
manifests despite normal IQ, adequate educational opportunity and in the absence of
any obvious sensory or neurological damage. According to the Phonological
Representations Hypothesis a core deficit for individuals with dyslexia across
languages is a brain-based difficulty in accurately storing the sound sequences that
make up words, or 'phonological' representations.
In this thesis the Phonological Representation Hypothesis (PRH) of dyslexia
was tested and elaborated. Twenty-four dyslexic children alongside chronological age
and reading age matched groups were assessed over a three-year period.
Consistent with the PRH, associations were found between the quality of the
dyslexic children's phonological representations, as indexed by picture naming, and
their performance on related input and output phonological processing tasks based on
the same lexical items.
Possible reasons for the underspecificity of dyslexic phonological
representations were also investigated at cognitive and perceptual levels. The sensitivity
of dyslexic individuals to the presence of similar-sounding words within their mental
lexicon, 'phonological neighbourhood density', was assessed. Across a range of
phonological awareness tasks the dyslexic group were found to be as sensitive to this
lexical factor as their age peers.
Perception of amplitude envelope onsets (AEOs) was also investigated. AEOs
are an auditory parameter associated with speech rhythm and were hypothesised here to
be important for the establishment of well-specified phonological representations.
Dyslexic insensitivity to AEO variation was seen longitudinally through both
behavioural and neurophysiological assessment. These findings suggest that for some
dyslexic children perception of basic rhythmic speech cues may play a role in their
phonological representation deficit