ISCA Workshop on Plasticity in Speech Perception (PSP2005)

Senate House, London, UK
June 15-17, 2005

Amplitude Envelope Onsets and Dyslexia: A Behavioural and Electrophysiological Study

Jenny Thomson (1), Torsten Baldeweg (2), Usha Goswami (1)

(1) University of Cambridge; (2) University College London, UK

With a core deficit in phonological representation widely accepted as a key feature of developmental dyslexia, the research field has moved to try and understand the underlying mechanisms of this phonological deficit. Many theories posit auditory perceptual causes, yet in the findings reported poor auditory skills only tend characterise a subset of the dyslexic group assessed. One reason for this may be that studies have tended to restrict their focus to acoustic cues acting within the transient time window of phonemic perception. If we take a developmental perspective, it may be more logical to examine acoustic cues within longer temporal time frames and working at a more basic level of speech processing, such as those associated with the amplitude envelope of the speech stream. Such cues are known to be important for very young infants when initially attempting to segment the stream of continuous speech around them. In previous behavioural studies we have found that amplitude envelope onset detection (AEOD) can be highly predictive of concurrent reading performance in school age dyslexic children and their controls across languages (Goswami et al., 2002; Richardson et al., 2004; Muneaux et al., 2004). This study aimed to characterise the neural correlate of the behavioural insensitivity to AEO rise time observed in dyslexic children. 8 dyslexic children (mean age 10 years) and 9 age-matched controls have participated to date. N1 potentials have been evoked to non-speech tones with 15ms and 90ms AEO rise times. The preliminary results show that whilst the amplitude of the N1 waveforms for the typicallydeveloping children varies as a function of AEO rise time, the dyslexic children's N1s exhibit no such differentiation. This finding supports the hypothesis that children with dyslexia have a developmental delay, manifest at a neural level, in their perception of basic auditory suprasegmental cues.

Bibliographic reference.  Thomson, Jenny / Baldeweg, Torsten / Goswami, Usha (2005): "Amplitude envelope onsets and dyslexia: a behavioural and electrophysiological study", In PSP2005, 190 (abstract).