The program in human sensory physiology divides its efforts between clinical service and research. Clinical services include universal newborn hearing screening (UNHS) and diagnosis of hearing loss in infants, young children, and patients with developmental disabilities represent the main efforts. These screening and diagnostic assessments are based on measurements of distortion-product otoacoustic emissions (DPOAE) and auditory brainstem responses (ABR), including ABR assessments using toneburst stimuli. The research program focuses on both basic and translational research efforts designed to increase our understanding of cochlear processing in humans with either normal hearing or hearing loss. Basic studies either have focused on issues associated with response growth, cochlear-amplifier gain, source contribution, differences in cochlear processing for high-frequency versus low-frequency stimuli, sources of variability in DPOAE responses, suppression of DPOAE responses, determining optimal stimulus conditions for eliciting DPOAEs, calibration of stimuli, and relations between OAE and ABR latencies for the same stimuli. Translational research efforts have focused on improvements in the diagnosis of hearing loss, predictions of threshold from objective measurements, the consequences of hearing loss on indirect estimates of cochlear-amplifier gain, and determining the extent to which objective measures of response growth correlate with subjective estimates of response growth, such as loudness, when hearing loss exists. A long-term goal of these efforts is to devise objective measures that will allow us to customize hearing-aid characteristics (such as compression threshold and compression ratio) for patients who are unable to describe their percepts of loudness.
Clinical studies are performed in a dedicated laboratory in the outpatient area of the hospital, although all sedated ABR procedures are performed in an inpatient room in the hospital with medical and nursing staff available. Clinical assessments are also performed at a satellite outpatient clinic, although all sedated ABRs are performed at the main hospital. UNHS is performed at an affiliated hospital at which there are 3000 births/year. The main clinical laboratory has a sound-isolated booth, two evoked-potential systems, one of which is portable and used for procedures conducted in inpatient rooms or the operating room. Additional equipment include systems for DPOAE measurements and measurements of middle-ear function. The research laboratory, which is separate from the clinical laboratory, has two double-walled sound booths, each of which is equipped with a PC that houses two DMA-controlled 24-bit soundcards and specialized hardware that is used to measure DPOAEs. In addition, the laboratory is equipped with a clinical audiometer and a middle-ear analyzer. Additional PCs are used for data analyses, preparation of figures, and manuscript preparation.
The clinical program is directed by Michael P. Gorga, Ph.D., with Jan Kaminski, R.EEG.T., Kathryn L. Beauchaine, M.A., Michelle Vogel, Au.D., Kendall Vincent, Au.D., and Ryan McCreery, M.A. responsible for the day-to-day provision of all clinical services. The research program, also Directed by Dr. Gorga, is co-directed by Stephen T. Neely, D.Sc., who also maintains an active research program in cochlear modeling. Other research staff include Judy Kopun, M.A., research laboratory manager, Hongyang Tan, M.S., data analyst, and one or two graduate students, typically from the Au.D. program at University of Nebraska-Lincoln.
Summary of Research Program
For Clinicians and Scientists
The research program focuses on cochlear nonlinearity in humans and on objective measures of threshold and suprathreshold consequences of hearing loss. Threshold studies are designed to more accurately identify ears with normal hearing and ear swith hearing loss. Work currently under way or recently completed address issues such as (1) the effects of frequency and level on DPOAE test performance, (2) optimizing DPOAE test performance through the use of multivariate analyses, optimal stimulus conditions, stimulus paradigms that control source contribution, and improved calibration procedures, (3) measurements of response growth based on DPOAE suppression measurements and the relation between these measurements and loudness growth in normal-hearing and hearing-impaired subjects, (4) measurement of DPOAE suppression in normal-hearing and hearing-impaired subject, and (5) changes in estimates of cochlear-amplifier gain and the gain-bandwidth tradeoff as a consequence of hearing loss. Several sub-projects are associated with each of these five general areas of research.
The clinical program is dedicated to providing state-of-art evaluations of hearing for infants, young children and patients who are unable to provide voluntary responses during hearing tests. The research program is concerned with finding better ways to assess the hearing of infants and young children. With all babies being screened for hearing as part of their birth admission, babies with hearing loss are being identified very early in life. It is essential that we have accurate descriptions of their hearing problems so that we can design an appropriate course of intervention. It is important that intervention begin quickly because babies learn much about speech and language early in life by hearing the speech of others. Accurate descriptions of their hearing problems enable us to provide appropriate rehabilitation services, thus minimizing the impact of hearing loss on speech and language development. Children with developmental disabilities often have hearing loss, but are unable to participate in behavioral hearing tests. It is imperative for us to be able to describe any hearing problems these children may have so that appropriate intervention can be provided and these children will be able to participate in society to the fullest level. For these reasons, a major focus of both our clinical evaluations and research program is the development and implementation of improvements in how we diagnose hearing loss in infants and young children.
Specific Areas of Research:
- Improving DPOAE test performance
- Predicting the magnitude of hearing loss from objective measurements
- Estimating cochlear tuning, cochlear-amplifier gain, cochlear compression, and response growth from DPOAE suppression measurements in both normal-hearing and hearing-impaired human subjects
- Relating objective and subjective measurements of response growth
- Comparing response latencies from OAE and ABR measurements
Professional Resources: Publication Lists
The link below opens a new window in PubMed1 where publications in archival, refereed journals are listed.