Judy R. Dubno
John H. Mills
Jayne B. Ahlstrom
Lois J. Matthews
Dept. of Otolarygol. and Commun. Sci., Medical Univ. of South Carolina, 171 Ashley Ave., Charleston, SC 29425-2242
Masked thresholds measured psychophysically are equivalent for young and aged human subjects with equal quiet thresholds. However, higher masked thresholds derived from auditory brain-stem responses (ABR) are observed for aged than for young gerbils, independent of quiet thresholds. The purpose of this exeriment was to characterize further age-related changes in masking by comparing masked thresholds measured electrophysiologically and psychophysically for young and aged humans with normal hearing. Signals were Gaussian 1.8-ms tone pips at 1.0, 2.0, and 4.0 kHz; the masker was a 1.0 kHz, low-pass-filtered noise. Using identical signals, ABR and behavioral thresholds were measured in quiet and in maskers with overall levels of 74, 82, and 90 dB SPL. Thresholds measured psychophysically are equivalent for young and aged subjects in both on- and off-frequency masking conditions, consistent with previous findings. However, quiet and masked ABR thresholds are higher for aged than for young subjects, and masking functions are shallower. Thus, whereas ABR thresholds of aged humans are higher than their behavioral thresholds, they are consistent with elevated ABR thresholds observed in aged gerbils. More direct comparisons of the characteristics of human and gerbil ABRs are contained in a companion poster. [Work supported by NIDCD.]