Growth of masking in listeners with cochlear impairments and impairments simulated by masking

Abstract

The higher‐than‐normal masked thresholds observed in many impaired listeners may be explained by nonlinear additivity of masking by the external masker and an hypothetical internal masker [Jesteadt et al., J. Acoust. Soc. Am. Suppl. 1 81, S77 (1987); Humes et al., J. Acoust. Soc. Am. Suppl. 1 81, S77 (1987)]. To test this hypothesis, Békésy tracking was used to measure growth‐of‐masking functions for 250‐ms tones with frequencies at and above those of continuous low‐pass or octave‐band noise maskers. Results for four impaired listeners show that the minimum‐effective‐masker levels (MEMLs, above which masking occurs) are higher than normal for small masker‐signal separations, Δf's, but approach normal values for larger Δf's. Above the MEMLs, masking grows 1 dB/dB or less. Results for simulated impairments are similar to those for real impairments, but MEMLs tend to be higher and masking often is less in simulated than in real impairments. These results indicate that nonlinear additivity of internal and external masking accounts for some, but not all, of the excessive spread of masking observed in many impaired listeners. [Work supported by NIH.]