Is There a Relationship Between Speech and Nonspeech Auditory Processing in Children With Dyslexia? (original) (raw)

2001, Journal of Speech Language and Hearing Research

Although there is good evidence that some dyslexic children show at least small deficits in speech perceptual tasks, it is not yet clear the extent to which this results from a general auditory, as opposed to a specifically linguistic/phonological problem. Here we have investigated the extent to which performance in backward and forward masking can explain identification and discrimination ability for speech sounds in which the crucial acoustic contrast (the second formant transition) is followed ("ba" vs. "da") or preceded ("ab" vs. "ad") by a vowel. More specifically, we expect children with elevated thresholds in backward masking to be relatively more impaired for tasks involving "ba" and "da" than for tasks involving "ab" and "ad". In order to determine whether poor performance with speech sounds reflects a general deficit for perceiving formant transitions, we also constructed nonspeech analogues of the speech syllables-the contrastive second formant presented in isolation. Two groups of 8 children matched for age (mean of 13 years) and nonverbal intelligence were selected to be well separated in terms of their performance in reading and spelling. All underwent the same set of auditory tasks: 1) forward, backward and simultaneous masking with a short (20 ms) 1-kHz probe tone in a broadband and notched noise; 2) identification as "b" or "d" of synthetic "ba"-"da" and "ab"-"ad" continua; 3) same/different discrimination of pairs of stimuli drawn from the endpoints of the two speech continua (e.g., "ba-da", "da-ba", "da-da", "baba"), as well as their nonspeech analogues. There were no differences between dyslexic and control children in forward and simultaneous masking, but thresholds for backward masking in a broadband noise were elevated for the dyslexics as a group. Overall speech identification and discrimination performance was superior for the controls (barely so for identification), but did not differ otherwise for the two speech contrasts (one of which should be influenced by backward masking, and one by forward). Thus, although dyslexics show a clear group deficit in backward masking, this has no simple relationship to the perception of crucial acoustic features in speech. Furthermore, the deficit for the nonspeech analogues was much less marked than for the speech sounds, with ¾ of the dyslexic listeners performing equivalently to controls. Either there is a linguistic/phonological component to the speech perception deficit, or there is an important effect of acoustic complexity.