First International School On Mind, Brain And Education

2005 July 16-20

Faculty of Education, University of Cambridge. UNITED KINGDOM

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Developmental trajectories of auditory perception in dyslexia: an ERP study
In previous studies we have found that sensitivity to auditory cues to speech rhythm (e.g., amplitude envelope onset or AEO detection, duration detection) are highly predictive of concurrent reading performance in dyslexic children and their controls, across languages (Goswami et al., 2002; Richardson et al., 2004; Muneaux et al., 2004). Sensitivity to some rhythmic cues account for up to 25% of the variance in reading, even after controlling for IQ.
Amplitude envelope onsets (AEOs) are important cues for speech rhythm, and are one of the earliest cues to word segmentation. They cause the percept of syllable ‘beats’. When the rise time of an AEO of a non-speech sound is short, an abrupt beat is heard, whilst longer rise times yield less abrupt beats. A deficit in AEO processing could thus affect an individual’s ability to segment the speech stream and so establish phonological representations.
Here we report findings from an electrophysiological study (using Event-related potentials, ‘ERP’) in which pre-attentive neural (N1) responses to varying AEOs to non-speech sounds were recorded. To date 8 dyslexic children (mean age 10 years) and 9 age-matched controls have participated. The preliminary results show that whilst the amplitude of the neural waveforms for typically-developing children vary as a function of AEO rise time, the dyslexic children’s waveforms exhibit no such differentiation and are more typical of younger children. This finding supports the hypothesis that children with dyslexia have a developmental delay, manifest at a neural level, in their perception of basic speech rhythm cues.