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plished the goal of providing considerable gain at low levels and increasingly smaller amounts of gain at higher levels. In a broad sense, compression hearing aids are attempting to restore the compression that is normally observed, and con- sequently extend the dynamic range of people with hearing loss. Although such aids may provide a more comfortable lis- tening environment, they unfortunately do not restore hear- ing to normal. Indeed, a review9 has shown that thus far they have had rather mixed success in terms of improving speech recognition in noisy environments. This may be at least part- ly related to the fact that the compression in hearing aids does not mimic the frequency selectivity that is observed in the compressive response of a normal cochlea. An important challenge, then, is to determine the best way to map the large range of acoustic levels in the environment to an auditory system that does not benefit from the compression that nor- mally exists at the basilar membrane in the cochlea.AT
Acknowledgments
The writing of this article was partially supported by a grant from the National Institute on Deafness and other Communication Disorders (NIDCD grant number DC01376). I thank Erica Williams for help with the figures and comments on an earlier draft.
References for further reading:
1. G. von Békésy, Experiments In Hearing. (McGraw-Hill, New York, 1960).
2. M.A.Ruggero,N.C.Rich,A.Recio,S.S.Narayan,andL.Robles, “Basilar-membrane responses to tones at the base of the chin- chilla cochlea,” J. Acoust. Soc. Am. 101, 2151–2163 (1997).
3. J. Zheng, W. Shen, D.Z. He, K.B. Long, L.D. Madison, and P. Dallos, “Prestin is the motor protein of cochlear outer hair cells,” Nature 405, 149–155 (2000).
4. H. Davis, “An active process in cochlear mechanics,” Hear. Res. 9, 79–90 (1983).
5. B.C.J. Moore and A.J. Oxenham, “Psychoacoustic consequences of compression in the peripheral auditory system” Psychol. Rev. 105, 108–124 (1998).
6. A.J. Oxenham and S.P. Bacon, “Cochlear compression: Perceptual measures and implications for normal and impaired hearing,” Ear and Hearing 24, 352–366 (2003).
7. A.J.OxenhamandS.P.Bacon,“Psychophysicalmanifestationsof cochlear compression: Normal-hearing listeners,” in Compression: From Cochlea to Cochlear Implants edited by S. P. Bacon, R. Fay, and A. N. Popper, pp. 62-106. (Springer Verlag, New York 2004).
8. S.P.BaconandA.J.Oxenham,“Psychophysicalmanifestationsof cochlear compression: Hearing-impaired listeners,” in Compression: From Cochlea to Cochlear Implants edited by S. P. Bacon, R. Fay, and A. N. Popper, pp. 107–152. (Springer Verlag, New York 2004).
9. H. Levitt, “Compression amplification,” in Compression: From Cochlea to Cochlear Implants edited by S. P. Bacon, R. Fay, and A. N. Popper, pp. 153–183. (Springer Verlag, New York 2003).
Sid P. Bacon received his PhD in experimental psychology from the University of Minnesota in 1985. Following postdoctoral positions at Cambridge University and Boys Town National Research Hospital, he joined the faculty at Vanderbilt University as an Assistant Professor and Director of Research. In 1988, he joined the faculty at Arizona State University, where he is a
Professor and the Chair of the Department of Speech and Hearing Science. Professor Bacon has been an associate edi- tor for the Journal of the Acoustical Society of America and the Journal of Speech, Language, and Hearing Research. He is a Fellow of the Acoustical Society of America and the American Speech Language Hearing Association. His research focuses on normal auditory processing and the effects of cochlear hearing loss on that processing.
34 Acoustics Today, April 2006