The role of auditory feedback in speech production was investigated by examining speakers’ phonemic contrasts produced under increases in the noise to signal ratio (N/S). Seven cochlear implant users and seven normal-hearing controls pronounced utterances containing the vowels /i/, /u/, /ε/ and /æ/ and the sibilants /s/ and /ʃ/ while hearing their speech mixed with noise at seven equally spaced levels between their thresholds of detection and discomfort. Speakers’ average vowel duration and SPL generally rose with increasing N/S. Average vowel contrast was initially flat or rising; at higher N/S levels, it fell. A contrast increase is interpreted as reflecting speakers’ attempts to maintain clarity under degraded acoustic transmission conditions. As N/S increased, speakers could detect the extent of their phonemic contrasts less effectively, and the competing influence of economy of effort led to contrast decrements. The sibilant contrast was more vulnerable to noise; it decreased over the entire range of increasing N/S for controls and was variable for implant users. The results are interpreted as reflecting the combined influences of a clarity constraint, economy of effort and the effect of masking on achieving auditory phonemic goals—with implant users less able to increase contrasts in noise than controls.
This research was supported by Grant No. R01-DC003007 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health. We are grateful to Dr. Donald Eddington of the Massachusetts Eye and Ear Infimary and Dr. Daniel Lee of the University of Massachusetts Medical Center for referring the implant users to the study, and to the implant users for their devotion of considerable amounts of their time. We also thank Advanced Bionics, Inc., and the Nucleus Corporation for their generous donations of research implant processors and three reviewers for their helpful comments on the manuscript.
1. Effects of masking noise
2. Loudness-target control experiment
C. Data extraction
1. Normal-hearing speakers
2. Cochlear implant users
C. Control experiment
A. Summary and interpretation of results
B. Relations to other findings and conclusions
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