Frequency-Discrimination Ability of Hearing-Impaired Listeners

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Abstract
Thresholds for frequency modulation were measured by an adaptive, two-alternative, forced-choice method with ten listeners: eight who showed varying degrees of sensorineural hearing impairment, and two with normal-hearing sensitivity. Results for test frequencies spaced at octave intervals between 125 and 4000 Hz showed that, relative to normal-hearing listeners, the ability of the hearing-impaired listeners to detect a sinusoidal frequency modulation: (1) is diminished above a certain level of hearing loss; and (2) is more disrupted for low-frequency tones than for high-frequency tones, given the same degree of hearing loss at the test frequency. The first finding is consistent with that of previous studies which show a general deterioration of frequency-discrimination ability associated with moderate, or worse, hearing loss. It is proposed that the second finding may be explained: 1) by differential impairment of the temporal and place mechanisms presumed to, encode pitch at the lower and higher frequencies, respectively; and/or, 2) for certain configurations of hearing loss, by the asymmetrical pattern of cochlear excitation that may lead to the underestimation, from measurements of threshold sensitivity, of hearing impairment for low-frequency tones and consequently to relatively large changes in frequency discrimination for small shifts in hearing threshold.

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