Much of the hospital's success in identifying and treating children with hearing loss is the result of the rapid transfer of research findings from laboratories to clinic and bedside.
Areas of Research - Clinical and Behavioral Studies of Human Communication - Physical Acoustics Laboratory
Overview
Our research is concerned with increasing our knowledge of the human middle ear and cochlea based upon acoustic response testing in the ear canal. Such tests are inherently noninvasive and lend themselves to clinical utilization. One project examines new forms of otoacoustic emissions (OAE), which may provide a clearer understanding of mechanical processes on the basilar membrane. Particular emphasis has been placed on stimulus-frequency OAEs, which yields data similar to behavioral tests of hearing, and on measuring and interpreting click-evoked OAEs at frequencies up to 16 kHz. A second project studies middle-ear mechanics using acoustical measurements and modeling. New screening and diagnostic tests of middle-ear function are in development that have clinical promise to improve assessment.
Facilities
The laboratory is equipped with computers for PC-based data acquisition and hearing assessment, a lock-in amplifier and a broad selection of transducers for acoustic measurements. Located in the laboratory are two sound-attenuated booths to facilitate data collection.
Staff
Douglas Keefe, Ph.D. is an acoustical physicist who has worked in hearing research, musical acoustics and related signal processing, acoustics and vibration fields. Chris Sanford, Ph.D. (Hearing Science, CCC-A) is a Postdoctoral Fellow with particular interests in pediatric audiology research with emphases in middle-ear and cochlear mechanics. Denis Fitzpatrick, Ph.D. (Medical Sciences Interdisciplinary Area) is a computer engineer who develops software for, and performs analyses in, ongoing projects. Yi-Wen Liu, Ph.D. (Electrical Engineering) is a Research Engineer with interests in cochlear mechanics, new technologies for hearing screening and diagnostic testing, and audio watermarking. Joshua Alexander, Ph.D., who is a Postdoctoral Fellow with primary emphasis on speech perception in listeners with sensorineural hearing loss, is also working on a research project involving speech-evoked otoacoustic emissions elicited by speech in quiet and in noise.
Summary of Research Program
For Clinicians and Scientists
A primary goal is to use a combination of acoustic and behavioral responses to test theories of auditory processing at the mechanical and behavioral levels. A subordinate goal is to relate acoustic responses measured non-invasively in the ear canal to cochlear and middle-ear function. One aim studies the relationships between middle-ear and cochlear mechanics using a combination of experimental and theoretical approaches. Measurements of otoacoustic emission (OAE) and acoustic transfer function (ATF) measurements are used to predict hearing loss. An improved test of acoustic-reflex function is used to study middle-ear noise sources and nonlinearity, and time-domain models of middle-ear and cochlear energy transmission are developed and evaluated based on experimental measurements. A second aim studies the effects of cochlear nonlinearity on spectral processing using stimulus frequency (SF) and click-evoked (CE) OAE stimulus conditions similar to those used in behavioral experiments on simultaneous and non-simultaneous masking and suppression. Experiments are addressing the extent to which OAE measurements of peripheral mechanics are able to non-invasively assess the strength of the medial olivo-cochlear (MOC) efferent system on outer hair cell function, assess the level dependence of SFOAE fine structure, and account for the performance of normal-hearing listeners and listeners with sensorineural hearing loss in detecting tones in quiet and noise conditions. A third aim studies the effects of cochlear nonlinearity on temporal processing using SFOAE stimulus conditions similar to those used in behavioral experiments on overshoot and amplitude modulation (AM). These experiments assess the shifts in SFOAEs that might be produced by activation of the MOC system in response to sounds with AM, and test the extent to which SFOAE measurements can account for measurements of behavioral overshoot in normal listeners . The results of the these experiments may provide useful data and modeling to improve our understanding of the auditory periphery in humans, and may improve our ability to diagnose the magnitude of hearing loss and improve our understanding of the impact of hearing loss on spectral and temporal resolution. Additional experiments are probing the relationship between OAEs and how speech is encoded in the cochlea.
Wideband (WB) reflectance and WB absorbance are names for an emerging type of acoustic ear-canal measurement that provides new dimensions for middle-ear assessment across a wide range of frequencies. Traditional types of aural immittance measurements are usually based on a single-frequency measurement of acoustic admittance, for example, at frequencies of 226 Hz or 1000 Hz, and do not provide a measure of middle-ear functioning over the full frequency range important for speech or music perception. Reflectance measurements are performed over a frequency range from 0.22 kHz up to approximately 8 kHz using a WB stimulus such as a click. Reflectance may be measured at ambient ear-canal pressure using a probe microphone and sound source similar to that used in recording OAEs, or as a a WB tympanogram by also varying static pressure within the ear canal. These WB tests have potential diagnostic use in children suspected of having otitis media with effusion (OME). Based on surgical confirmation of fluid following a myringotomy, WB absorbance is accurate at classifying whether middle-ear effusion is present or not, and at predicting the presence of a conductive hearing loss in children with OME. Furthermore, these WB tests can detect the presence of transient middle-ear dysfunction in infants referred by a newborn hearing screening (NHS) exam based on a distortion-product (DP)OAE test, the so-called false positives in NHS. Such testing also included a WB test of middle-ear muscle reflex threshold.
Families
The laboratory research is concerned with devising better ways to assess how the middle ear and inner ear function, and to find new techniques for identifying hearing loss in infants, young children, and adults. One project may improve the detection of middle-ear fluid in the ears of young children, a condition which is associated with the pain and discomfort of earaches in young children. Another project has special relevance for improving newborn hearing screening programs to detect hearing loss, by testing whether the middle ears of infants tested just hours after birth in the birthing hospital function differently from the middle ears of infants only a few days later. Improved methods of detecting hearing loss and related conditions are essential to referring children and adults to health specialists for rehabilitative services.
Specific Areas of Research:
Experimental and theoretical studies of cochlear and middle-ear mechanics
Professional Resources: Recent presentations
Sanford, C.A., Fitzpatrick, D., Keefe, D.H., Lewis, D.E., Liu, Y.-W., McCreery, R., and Gorga, M.P. (2008). Wideband energy reflectance predicts transient middle-ear dysfunction in neonates. American Auditory Society meeting, Scottsdale, AZ (March).
Liu, Y.-W., Cohn, E., Ellison, J., Fitzpatrick, D., Gorga, M., Gortemaker, M., Sanford, C., and Keefe, D.H (2008). Wideband acoustic reflectance, including wideband tympanometry and acoustic-reflex thresholds: System development and results on children with middle-ear fluid and adults. Assoc. Res. Otolaryngol. meeting, Phoenix, AZ (February).
Keefe, DH and Gorga MP (2007). Wideband reflectance measures of middle-ear functioning. Technology Keynote lecture at the American Speech-Language-Hearing Association (ASHA) Convention, Boston MA (November).
Professional Resources: Publication Lists
Each link below opens a new window in PubMed1 in which the author’s biomedical publications are listed.
1PubMed is a service of the U.S. National Library of Medicine that includes citations from MEDLINE and other life science journals for biomedical articles back to the 1950s. PubMed includes links to full text articles and other related resources. Please note that publications from other authors with the same name may also be listed.