Abstract
Developmental dyslexia is consistently associated with difficulties in processing phonology (linguistic sound structure) across languages. One view is that dyslexia is characterised by a cognitive impairment in the “phonological representation” of word forms, which arises long before the child presents with a reading problem. Here we investigate a possible neural basis for developmental phonological impairments. We assess the neural quality of speech encoding in children with dyslexia by measuring the accuracy of low-frequency speech envelope encoding using EEG. We tested children with dyslexia and chronological age-matched (CA) and reading-level matched (RL) younger children. Participants listened to semantically-unpredictable sentences in a word report task. The sentences were noise-vocoded to increase reliance on envelope cues. Envelope reconstruction for envelopes between 0 and 10Hz showed that the children with dyslexia had significantly poorer speech encoding in the 0–2Hz band compared to both CA and RL controls. These data suggest that impaired neural encoding of low frequency speech envelopes, related to speech prosody, may underpin the phonological deficit that causes dyslexia across languages.
Highlights
Children with developmental dyslexia have difficulty in processing the phonological aspects of speech, across languages (Ziegler & Goswami, 2005, for review)
Participants comprised all children in the cohort who volunteered for EEG: 12 children with dyslexia (DY), 23 typically-developing children matched for chronological age (CA), and 11 matched for reading level (RL, see Table 1 for detail)
This study is the first to reveal that when listening to sentences, neural encoding of the low-frequency amplitude information in speech at the single sentence level is significantly worse in children with dyslexia compared to both CA-matched and RL-matched control children
Summary
Children with developmental dyslexia have difficulty in processing the phonological aspects of speech, across languages (Ziegler & Goswami, 2005, for review) They are poor at making decisions about whether words rhyme with each other (‘‘cat” ‘‘hat”), at counting syllables in words (‘‘caterpillar” has 4 syllables), at detecting syllable stress (‘‘difficulty” has first syllable stress) and at deleting individual speech sounds (phonemes: ‘‘star” without the ‘‘s” sound leaves ‘‘tar”) (e.g., Bradley & Bryant, 1978, English; Wimmer, 1993, 1996, German; Share & Levin, 1999, Hebrew; Kim & Davis, 2004, Korean). Current remediation relies on intensive phonological training at the phoneme level accompanied by training in letter-sound correspondences (e.g., Brem et al, 2010; Schneider, Roth, & Ennemoser, 2000)
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