Loudness growth under masking: relation to true sensorineural impairment.

Abstract

Alternate binaural loudness balances between masked and unmasked normal ears were performed to examine the growth of loudness as a function of masker level at each of several frequencies (500, 1000, 2000, and 4000 Hz) and to determine whether the recruitmentlike phenomenon in masked ears is comparable in its growth and form to actual recruitment growth in sensorineural impaired ears. The results for 28 subjects indicated that for all frequencies a power function relating the perceived loudness in the masked ear to the unmasked ear could be drawn, and that the slope of this function rose as a function of increased masking. The family of slopes for each frequency was linearly related to the induced threshold shift. The slope of this latter relation proved to be frequency dependent. Comparison between the slope growth in simulated hearing loss and the family of loudness-balance slopes obtained from patients with true unilateral loss of varying degree indicated that the slopes of loudness-balance functions in the latter group also increased linearly with increased loss. In this latter instance, however, the slope growth was not frequency dependent, thus pointing to an essential difference between simulated and actual loudness recruitment growth.