Is there a relationship between speech and nonspeech auditory processing in children with dyslexia?

A group of 8 young teenagers with dyslexia were compared to age-matched control participants on a number of speech and nonspeech auditory tasks. There were no differences between the control participants and the teenagers with dyslexia in forward and simultaneous masking, nor were there any differences in frequency selectivity as indexed by performance with a bandstop noise. Thresholds for backward masking in a broadband noise were elevated for the teenagers with dyslexia as a group. If this deficit in backward masking had an influence on speech perception, we might expect the perception of "ba" versus "da" to be affected, as the crucial second formant transition is followed by a vowel. On the other hand, as forward masking is not different in the two groups, we would expect the perception of "ab" versus "ad" to be unaffected, as the contrastive second formant transition is preceded by a vowel. Overall speech identification and discrimination performance for these two contrasts was superior for the control group but did not differ otherwise. Thus, the clear group deficit in backward masking in the group with dyslexia has no simple relationship to the perception of crucial acoustic features in speech. Furthermore, the deficit for nonspeech analogues of the speech contrasts (second formants in isolation) was much less marked than for the speech sounds, with 75% of the listeners with dyslexia performing equivalently to control listeners. The auditory deficit cannot therefore be simply characterized as a difficulty in processing rapid auditory information. Either there is a linguistic/phonological component to the speech perception deficit, or there is an important effect of acoustic complexity.