Abstract
As hearing aid technology becomes more and more complicated, it becomes more difficult to determine the optimal hearing aid characteristics for a specific client. One important goal of hearing aid fittings is to improve speech recognition performance of the hearing aid user. Both generic and manufacturer-default prescriptive hearing aid fitting procedures have traditionally focused on audibility and comfort of amplified speech and deal mostly with the placement of the long-term average speech spectrum within the dynamic range of the listener. The multiple forms of signal processing used simultaneously in current hearing aids do much more than control the level of the amplified signal. The signal processing causes complicated changes to the temporal and spectral characteristics of the amplified speech signal.
When the hearing aid user does not obtain improved speech recognition performance or when improvement is not adequate, the current techniques for validating hearing aid performance will not necessarily explain the reasons for poor speech recognition performance. Is the problem due to changes introduced to the speech by the hearing aid, the auditory system, or the brain? In this issue of Trends in Amplification, researchers from the University of Washington, Seattle, present their ideas and research about how to assess the effect of hearing aid processing on speech.
In the first article of this issue, Pamela Souza and Kelly Tremblay provide a framework for understanding the interaction between the signal, the hearing aid, and the individual hearing aid user. They identify and describe methods that may be used to document the effect of the hearing aid on the speech signal and the combined effect of the hearing aid and the auditory system on the signal reaching the brain.
The companion articles are coauthored by members of the University of Washington research team. These articles report on feasibility studies designed to determine how measurement techniques currently used for research might be transferred to clinical practice. The article by Caldwell, Souza, and Tremblay reports on the effect of probe insertion depth on real ear measures of amplified speech. The final article, by Tremblay, Kalstein, Billings, and Souza, reports on a study to determine whether cortical evoked potentials can be used to monitor the effectiveness of amplification. Together, these articles provide an exciting glimpse of assessment techniques that may one day become part of a protocol for hearing aid fitting and assessment.
About the Authors
Pamela Souza received her BS from the University of Massachusetts at Amherst and her MS and PhD from Syracuse University. She is an associate professor at the University of Washington, Seattle, where she teaches courses in hearing aids, hearing science, and diagnostic audiology. Her research has focused on the effects of nonlinear amplification, particularly in older listeners; how temporal discrimination changes with age; and the consequences of multichannel wide-dynamic range compression on perception of speech cues by listeners with severe hearing loss. Her research is currently supported by the National Institutes of Health and the Department of Veterans Affairs.
Kelly Tremblay received her BS from the University of Western Ontario, her MS from Dalhousie University, and her PhD from Northwestern University. She is an associate professor at the University of Washington, Seattle, where she teaches courses in electrophysiology, diagnostic audiology, and related topics. Her research has focused on how listening training alters the neurophysiologic representation of speech in the central auditory system and the effects of aging and age-related hearing loss on the brain's ability to compensate for hearing loss. Her research is currently supported by the National Institutes of Health.
Curtis Billings received his BS in speech and hearing science from the University of Utah and his MS in audiology from the University of Washington, Seattle. He has worked as a clinical audiologist for the Veteran's Administration and taught coursework in hearing aids and electrophysiology. He is currently completing a PhD in audiology at the University of Washington, Seattle, where his research interest is in electrophysiologic measures of hearing aid performance.
Marc Caldwell received his BS in microbiology from Eastern Washington University and a clinical doctorate in audiology from the University of Washington, Seattle. While at the University of Washington, his research was related to the spectral and temporal characteristics of amplified speech. He works as a clinical audiologist for Bay Audiology in New Zealand.
Laura Kalstein received a BS in speech, language, and hearing science from the University of Colorado at Boulder and an MS in audiology from the University of Washington, Seattle. Her current professional interests include provision of cochlear implant services. She is an audiologist at the Colorado Hearing and Balance Clinic, Colorado Springs, Colorado.