Objectives: The purpose of this study was to obtain behavioral hearing thresholds for frequencies between 0.125 and 20 kHz from a large population between 10 and 65 yr old using a clinically feasible calibration method expected to compensate well for variations in the distance between the eardrum and an insert-type sound source. Previous reports of hearing thresholds in the extended high frequencies (>8 kHz) have either used calibration techniques known to be inaccurate or specialized equipment not suitable for clinical use.
Design: Hearing thresholds were measured from 352 human subjects between 10 and 65 yr old having clinically normal-hearing thresholds (<20 dB HL) up to 4 kHz. An otoacoustic emission probe fitted with custom sound sources was used, and the stimulus levels individually tailored on the basis of an estimate of the insertion depth of the measurement probe. The calibrated stimulus levels were determined on the basis of measurements made at various depths of insertion in a standard ear simulator. Threshold values were obtained for 21 frequencies between 0.125 and 20 kHz using a modified Békésy technique. Forty-six of the subjects returned for a second measurement months later from the initial evaluation.
Results: In agreement with previous reports, hearing thresholds at extended high frequencies were found to be sensitive to age-related changes in auditory function. In contrast with previous reports, no gender differences were found in average hearing thresholds at most evaluated frequencies. Two aging processes, one faster than the other in time scale, seem to influence hearing thresholds in different frequency ranges. The standard deviation (SD) of test–retest threshold difference for all evaluated frequencies was 5 to 10 dB, comparable to that reported in the literature for similar measurement techniques but smaller than that observed for data obtained using the standard clinical procedure.
Conclusions: The depth-compensated ear simulator-based calibration method and the modified Békésy technique allow reliable measurement of hearing thresholds over the entire frequency range of human hearing. Hearing thresholds at the extended high frequencies are sensitive to aging and reveal subtle differences, which are not evident in the frequency range evaluated regularly (≤8 kHz). Previously reported gender-related differences in hearing thresholds may be related to ear-canal acoustics and the calibration procedure and not because of differences in hearing sensitivity.
Behavioral-hearing thresholds were measured between the frequencies of 0.125 to 20 kHz for 352 clinically normal hearing subjects, ranging in age between 10 and 65 yr. A depth-compensated ear simulator method was used to calibrate stimulus levels at the eardrum, based on an acous-tic estimate of the insertion depth of the measurement probe for each subject. The results were in general agreement with previous reports of hearing thresholds measured over this frequency range, although using less practical or less accurate calibration techniques. These results con-firmed the sensitivity of hearing thresholds above 8 kHz to aging processes. They also revealed possible multiple, frequency-dependent aging processes that have not been reported before. In contrast with previous reports, age-matched groups of male and female subjects did not show statistically significant differences in average thresholds. Test-retest variability was evaluated in 49 subjects and found to be comparable with that reported in the literature.
1The Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, Illinois
2The Hugh Knowles Center, Northwestern University, Evanston, Illinois
3Department of Preventive Medicine, Biostatistics Collaboration Center, Chicago, Illinois
Address for correspondence: Jungmee Lee, PhD, 2-256 Frances Searle, 2240 Campus Drive, Communication Sciences and Disorders, Northwestern University, Evanston, IL 60208, USA. E-mail: firstname.lastname@example.org.
The authors thank Gayla Poling for her valuable comments. The authors also thank Erica Choe, Helen Han, Lauren Hardies, Kelly Waldvogel, Coryn Weissinger, Darrin Worthington, and Wei Zhao for their help in data collection. Kathleen Dunckley and Lauren Calandruccio participated in many stimulating discussions related to these data. Vickie Hellyer managed research subject recruitment and participation.
This work was supported by grant R01 DC008420 from the National Institute on Deafness and Other Communication Disorders. This work was also supported by Northwestern University.
Presented in a poster at the 32nd Midwinter Meeting of the Association for Research in Otolaryngology.
Received June 6, 2011
Accepted October 16, 2011