Masking and aging: I. Gerbil auditory brain‐stem response thresholds

Masked thresholds estimated from auditory brain‐stem responses (ABR) of aging gerbils are 20–30 dB higher than the masked thresholds of young gerbils when quiet thresholds are equal. In this presentation, we will discuss data on young (6 month) gerbils with normal hearing and aged (36 month) gerbils with a range of hearing levels. ABR thresholds were measured at 1, 2, 4, 8, and 16 kHz in quiet and in the presence of a low‐pass filtered noise (1 kHz upper bound) at levels of 50, 60, and 70 dB SPL. Young subjects had linear growth of masking of signals within the passband of the noise. At higher frequencies, only minimal masking was observed. In contrast, aged subjects showed much higher masked thresholds at 2 and 4 kHz compared to young subjects. This occurred for both aged subjects with minimal age‐related threshold elevation and those with large hearing losses. In accordance with previous studies, masked ABR thresholds in aging gerbils are much higher than those in young gerbils. This phenomenon is examined in human subjects with behavioral and ABR techniques in the companion presentations. [Work supported by NIDCD.]