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 - Clinical Sensory Physiology

Overview

The program in clinical sensory physiology divides its efforts between clinical service and research. On the clinical side, universal newborn hearing screening and diagnosis of hearing loss in infants, young children, and patients with developmental disabilities represent the main efforts. These clinical assessments are based on measurements of distortion product otoacoustic emissions (DPOAE) and auditory brainstem responses (ABR), including ABRs elicited by toneburst stimuli. Other clinical activities include electrophysiological evaluations of patients suspected of having disorders affecting lower brainstem pathways. Vestibular evoked myogenic potentials are also measured as part of the assessments of dizzy patients.

The research program focuses on both basic and translational research efforts. A main focus of these efforts relates to understanding cochlear processing in humans with either normal or impaired hearing. Basic studies either have been conducted or are currently under way that address questions related to response growth, cochlear-amplifier gain, source contributions to DPOAE responses, differences in cochlear processing for high-frequency and low-frequency stimuli, sources of variability in normal DPOAE responses, DPOAE suppression, determining optimal stimulus conditions for eliciting DPOAE responses, and calibration of stimuli. Translational research efforts have focused on improvements in the diagnosis of hearing loss, loss of compression as a consequence of cochlear damage, and determining whether response growth can be estimated in ears with hearing loss. A long-term goal of these latter studies is to determine the extent to which behavioral estimates of response growth, such as loudness recruitment, can be predicted from objective measures, such as DPOAE input/output functions and DPOAE suppression. This work is important because it could lead to the objective selection of hearing-aid characteristics, such as compression threshold and compression ratio, for patients who are unable to describe their percepts of loudness.

Facilities

The clinical efforts are conducted mainly in a laboratory in the outpatient area, although all sedated ABR procedures are performed in an inpatient room in the hospital with nursing and medical staff available. The clinical laboratory has a sound-isolated booth in which testing is performed. Equipment includes two evoked-potential systems, one of which is portable and used for procedures in other areas of the hospital, such as the inpatient room or the operating room. Additional equipment include systems for DPOAE measurements and measurement of middle-ear functions The research 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 for the measurements of DPOAEs (Etymotic ER-10C low-noise probe-microphone systems). In addition, the laboratory has equipment that is used to screen for middle-ear dysfunction. Two additional PCs are available for data analyses, plotting, manuscript preparation, and other activities. OAEs and ABRs are measured with custom-designed software, each of which incorporates features needed for experimental measurements, such as DPOAE I/O functions, DPOAE suppression, and ABR masking.

Staff

The clinical sensory physiology program is directed by Michael P. Gorga, Ph.D., who is responsible for both clinical and research efforts. Jan Kaminski, R.EEG.T., Kathryn L. Beauchaine, M.A., Michelle Vogel, Au.D., and Kendell Vincent, Au.D. are responsible for the day-to-day services provided in the clinical laboratory, on the inpatient floor, in the operating room, and Ryan McCreery, M.A. manages testing in the newborn and intensive care nurseries. Stephen T. Neely, D.Sc., actively participates in the design and execution of all studies conducted in the research laboratory and is responsible for the development of laboratory software. Judy Kopun, M.A., serves as research laboratory manager, and is assisted by Darcia Dierking, M.A.. Hongyang Tan, M.S. assists with data analyses. In addition, Au.D. and Ph.D. students may be working in the laboratory at any time.

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 ears with hearing loss. Work currently under way or completed addresses issues such as (1) the effect of stimulus frequency and level on DPOAE test performance, (2) the use of multivariate analyses to improve the accuracy of DPOAE tests in dichotomous decisions about auditory status, (3) predicting auditory thresholds from DPOAE data, (4) DPOAE I/O measurements of response growth, (5) DPOAE suppression measurements to estimate response growth and cochlear-amplifier gain, (6) estimates of peripheral tuning based on DPOAE suppression tuning curves in normal and impaired ears, (7) sources of variability in DPOAE measurements, (8) optimizing stimuli for eliciting DPOAEs, (9) calibration of stimuli for DPOAE measurements, (10) evaluating cochlear processing differences for low-frequency and high-frequency stimuli, (11) determining the influence of calibration method on DPOAE test performance, (12) comparing behavioral and acoustical estimates of cochlear-amplifier gain and growth of masking/suppression, and (13) determining the relationship between objective and behavioral measurements of response growth.

For Families

Overall, the work in the clinical sensory physiology program is concerned with finding better ways to assess the hearing of infants, young children, and patients whose developmental level prevents them from providing voluntary responses to sound. With all babies being screened for hearing loss at birth, 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 very 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 and research programs is the development and implementation of improvements to how we diagnose hearing loss in infants and young children.

Professional Resources: None.


Specific Areas of Research:

1. Improving DPOAE test performance
2. Predicting the magnitude of hearing loss from DPOAE measurements
3. Estimating cochlear tuning from DPOAE suppression measurements
4. Using DPOAE I/O functions to estimate the amount of cochlear compression
5. Estimating the gain of the cochlear amplifier from suppression measurements
6. Relating objective (OAE) and subjective (behavioral) measurements of response growth
7. Determining how cochlear, auditory-nerve, and higher cortical responses contribute to behavioral masking
8. Comparing cochlear function for high-frequency and low-frequency stimuli
9. Determining the influence of source contribution on DPOAE test performance
10. Determining optimal stimulus conditions for DPOAE measurements
11. Evaluating factors that influence normal variability in DPOAE responses
12. Development of improved calibration procedures
13. Evaluation of the impact of calibration procedure on DPOAE test performance