Phase effects in forward masking for normally hearing and hearing-impaired subjects

Abstract

The forward masking produced by harmonic complex tones depends on the phases of the masker components; phases giving ‘‘peaky’’ waveforms on the basilar membrane result in less forward masking than phases giving less peaky waveforms. This difference has been attributed to the effects of peripheral compression and suppression, which depend on the active mechanism in the cochlea. Hence, no phase effect would be expected for subjects with moderate cochlear hearing loss. Growth-of-masking functions were measured for forward maskers containing the first 40 harmonics of a 100-Hz fundamental, with components added in cosine (C) or random (R) phase. The signal frequency was 1 or 2 kHz. For three normally hearing subjects, the R masker produced considerably more masking than the C masker, at high masker levels. Of four subjects with moderate cochlear hearing loss, one showed no effect of masker phase, but for the other three there was a significant effect for at least one signal frequency. It is suggested that peripheral compression and suppression play a role in the phase effect, but other factors, possibly depending on the operation of the efferent system, are involved. [Work supported by MRC (UK).]