Neural evidence of allophonic perception in children at risk for dyslexia.

Learning to read is a complex process that develops normally in the majority of children and requires the mapping of graphemes to their corresponding phonemes. Problems with the mapping process nevertheless occur in about 5% of the population and are typically attributed to poor phonological representations, which are--in turn--attributed to underlying speech processing difficulties. We examined auditory discrimination of speech sounds in 6-year-old beginning readers with a familial risk of dyslexia (n=31) and no such risk (n=30) using the mismatch negativity (MMN). MMNs were recorded for stimuli belonging to either the same phoneme category (acoustic variants of /bə/) or different phoneme categories (/bə/ vs. /də/). Stimuli from different phoneme categories elicited MMNs in both the control and at-risk children, but the MMN amplitude was clearly lower in the at-risk children. In contrast, the stimuli from the same phoneme category elicited an MMN in only the children at risk for dyslexia. These results show children at risk for dyslexia to be sensitive to acoustic properties that are irrelevant in their language. Our findings thus suggest a possible cause of dyslexia in that they show 6-year-old beginning readers with at least one parent diagnosed with dyslexia to have a neural sensitivity to speech contrasts that are irrelevant in the ambient language. This sensitivity clearly hampers the development of stable phonological representations and thus leads to significant reading impairment later in life.

Allophonic mode of speech perception in Dutch children at risk for dyslexia: a longitudinal study.

There is ample evidence that individuals with dyslexia have a phonological deficit. A growing body of research also suggests that individuals with dyslexia have problems with categorical perception, as evidenced by weaker discrimination of between-category differences and better discrimination of within-category differences compared to average readers. Whether the categorical perception problems of individuals with dyslexia are a result of their reading problems or a cause has yet to be determined. Whether the observed perception deficit relates to a more general auditory deficit or is specific to speech also has yet to be determined. To shed more light on these issues, the categorical perception abilities of children at risk for dyslexia and chronological age controls were investigated before and after the onset of formal reading instruction in a longitudinal study. Both identification and discrimination data were collected using identical paradigms for speech and non-speech stimuli. Results showed the children at risk for dyslexia to shift from an allophonic mode of perception in kindergarten to a phonemic mode of perception in first grade, while the control group showed a phonemic mode already in kindergarten. The children at risk for dyslexia thus showed an allophonic perception deficit in kindergarten, which was later suppressed by phonemic perception as a result of formal reading instruction in first grade; allophonic perception in kindergarten can thus be treated as a clinical marker for the possibility of later reading problems.