Masking period patterns in normal-hearing and hearing-impaired listeners.

Abstract

Masking period patterns (MPPs), developed by Zwicker [J. Acoust. Soc. Am. 59, 166–175 (1976)] as a psychophysical correlate of the physiological period histogram, were obtained from four normal-hearing and four cochlear hearing-impaired subjects. The just audible level of a brief, relatively high-frequency, test tone was measured as a function of its temporal position within the period of a 40-Hz masker. Zwicker’s findings were replicated in normal listeners. At low masker levels a single maximum (Max 1) was observed between 0 and 90 deg of the masker period. At higher masker levels a second maximum (Max 2) developed between 180 and 270 deg. Zwicker’s model [Biol. Cyb. 23, 49–60 (1976)] suggests that Max 1 reflects level-independent suppression effects and Max 2 reflects some combination of level-dependent excitation and suppression effects, which is consistent with physiological biasing data. For impaired listeners, in regions of hearing loss, the degree of modulation in the MPP was reduced relative to that seen in normal-hearing listeners. The pattern of modulation was usually altered as well. These results are discussed in the context of outer hair cell damage at the place in the cochlea corresponding to the test tone frequency. [Supported by NIDCD.]