The effect of multichannel compression on vowel and stop-consonant discrimination in normal-hearing and hearing-impaired subjects.
OBJECTIVE
Multichannel compression (MCC) processing can alter the speech spectrum, perhaps reducing spectral contrasts that are important for the discrimination of certain speech sounds. The effect of MCC processing on the discrimination of vowels and voiced stop consonants was studied.


METHODS
Vowels and voiced stop consonants were MCC-processed in two ways: 1) FLAT MCC having the same compression ratio in each channel, and 2)SHAPED MCC having compression ratios in each channel adjusted to the auditory area of the particular subject. The stimuli were processed both ways using 2, 4, 8, 16, and 31 independent compression channels. Unprocessed and linearly amplified stimuli were used as control conditions. Normal-hearing and hearing-impaired subjects were tested for changes in discrimination performance as a function of the MCC processing parameters.


RESULTS
When the MCC processing was adjusted specifically for an individual hearing impared subject, no negative effect of increasing numbers of channels (2 to 31)was found. In the case of FLAT MCC processing, increasingly degraded discrimination performance was found for both subject groups as the compression ratio increased and as the number of channels increased. There was also a strong interaction between the effects of the number of channels and the compression ratio, with the negative effects of increasing numbers of channels being much greater at the highest compression ratio.


CONCLUSIONS
Negative effects of MCC were found only for very extreme MCC conditions. MCC processing with compression ratios adjusted in each channel for the individual subject, and having as many as 31 channels, revealed no negative effects on vowel or voiced stop-consonant discrimination. These results do not support the prevalent view that MCC with more than two or three channels will be detrimental and should encourage further research on MCC processing with larger numbers of channels.
Crain
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TR
Sensorineural Hearing Loss Research Laboratory, Veterans Affairs Medical Center, Martinez, California, USA.
Yund
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EW
D001309:Auditory Threshold; D006309:Hearing / Q000502:physiology*; D006319:Hearing Loss, Sensorineural / Q000175:diagnosis*; D006801:Humans; D010700:Phonetics; D013063:Speech Discrimination Tests; D013067:Speech Perception