New research among dyslexic adults seems to confirm that dyslexics have a heightened sensitivity to sounds of language, thinking in an allophonic mode rather than focusing on phonemic units. Allophones are the smallest units of sounds that can be discerned in language; phonemes are made up of groups of allophones that have linguistic significance. For example, the /th/ sound is softer as pronounced in the word “this” than in different in the word “thick,” but both sounds are always spelled with the same letter combination in English.
An allophonic perceptual mode would mean that dyslexics are sensitive to phonetic variations that are irrelevant to understanding or writing their language. To explore this possibility, researchers used EEG to measure the mental response of adult dyslexics and control subjects while listening to sounds along the /bə – də/ continuum. Both groups showed similar brain wave activity when listening to different phonemes, but only the dyslexic listeners showed a continued mismatch negativity response when listening to different sound within the same phonemic category.
A “mismatch negativity” response is a brain wave spike triggered when a person perceives an auditory change. In this study the brain wave evidence confirms that dyslexic listeners hear more rather than less when attending to the sounds of language. This explains why dyslexics commonly have difficulties with reading and spelling, but suggests that remedial instruction to teach letter / sound correspondence may be on the wrong track and potentially add to a student’s confusion.
Mark W. Noordenbos, Eliane Segers, Willy Serniclaes, Ludo Verhoeven. Neural evidence of the allophonic mode of speech perception in adults with dyslexia. Clinical Neurophysiology, Available online 8 February 2013 http://dx.doi.org/10.1016/j.clinph.2012.12.044
Related Blog Post:
Phonemic Awareness – A Different Take (October 2012)