Effects of Remediation on Auditory Temporal Processing in Dyslexia: An Overview

Auditxory Temporal Processing in Dyslexia

Auditory temporal processing refers to the processing of temporal properties of the acoustic signal (Nittrouer, 1999). Fundamental temporal processing problem leads to speech processing impairments, which in turn have deleterious impact on reading development. Temporal processing speed deficit across modalities might be the cause of difficulties in dyslexia. Dyslexic children have language problems that result from their [Page 246]inability to perceive the rapid acoustic elements included in human speech. Phonetic processing deficits might result from deficiencies of the mechanisms crucial for processing rapidly changing acoustic signals (Tallal, 1984). A large body of evidences indicates that children and adults with language problems have difficulties in phonological processing. Phonological processing refers to awareness and manipulation of the phonological structure of language. Children with reading difficulties have problem in segmenting syllables into phonemes whereas good readers do not have this problem. It has also been proposed that phonetic distance and not the temporal order difficulty may be reflected in the dyslexic's poor performance on temporal order judgement tasks (Mody et al., 1997).

Children with reading difficulties have problems in recalling the order of a series of non-speech sounds if they are presented rapidly and also if the duration of the sounds in also about 100 ms or shorter (Tallal, 1980). These findings have been the initial evidences for the fact that children with reading difficulties have problem in identifying or sequencing short duration stimuli presented in rapid succession (Merzenich et al., 1996). The relationship between temporal processing and phonological processing ability has been hypothesized to propose that temporal processing deficits have their effect on phonological processing at the level of speech perception. Phonological processing deficits are one of the fundamental deficits in reading impaired children. Children with reading disability make more errors in recalling the correct order of rapidly presented sounds. Dyslexics perform worse on tasks which need rapid sequential processing and this impairment could involve both the visual and auditory modalities and might cause dyslexia (Eden et al., 1995). In a study on 19 dyslexics, Mismatch Negativity (MMN) was determined for tones and speech stimuli and the results showed no differences between dyslexics and non-dyslexics with tones but significantly attenuated MMN for speech stimuli, thereby confirming a specific speech processing deficit at sensory level (Schulte- Korne et al., 1998). MMN could be taken as a tool for early identification of dyslexia but studies are required to show if MMN could be a predictor of later reading disability.

...