Low-frequency hearing loss: perception of filtered speech, psychophysical tuning curves, and masking

Abstract

Two subjects with low-frequency hearing loss were evaluated to determine whether their responses to low-frequency stimulation might be a result of stimulation of nerve fibers with higher characteristic frequencies. One subject showed large low-frequency threshold shifts in the presence of high-pass noise or a 2000-Hz tonal masker. Psychophysical tuning curves for 500- and 800-Hz probe signals were peaked above 2000 Hz. This subject was also tested with high-pass, low-pass, and unfiltered speech both in quiet and in the presence of a high-pass noise masker. Results were interpreted as showing relatively little encoding of low-frequency speech by high-frequency nerve fibers. The second subject had masking patterns and psychophysical tuning curves which were most consistent with detection of low-frequency signals by nerve fibers with low characteristic frequencies. Psychophysical tuning curves of both subjects were compared to those obtained from subjects with high-frequency hearing loss. Implications for the diagnosis of low-frequency hearing loss and the use of hearing aids are discussed. [Work supported by NIH.]