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

Four subjects with low-frequency hearing loss were evaluated to determine whether their responses to low-frequency stimulation might be the result of stimulation of nerve fibers with higher characteristic frequencies. Two masking paradigms were employed to indirectly investigate the contribution of high-frequency nerve fibers to the detection of low-frequency stimuli: (1) masking of a low-level, fixed-frequency probe by a variable-frequency pure-tone masker (psychophysical tuning curve) and (2) masking of pure tones by a high-level, fixed-frequency pure-tone masker. Low-frequency remote masking by tones and displacements in the tips of tuning curves to higher frequencies were interpreted as evidence that low-frequency signals near threshold were being detected by high-frequency fibers in three of the subjects. Three subjects were 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 a relatively small contribution of high-frequency fibers to the perception of low-frequency speech.