The effect of basilar-membrane nonlinearity on the shapes of masking period patterns in normal and impaired hearing

Masking period patterns (MPPs) were measured in listeners with normal and i mpaired hearing using amplitude-modulated tonal maskers and short tonal pro bes. The frequency of the masker was either the same as the frequency of th e probe ton-frequency masking) or was one octave below the frequency of the probe toff-frequency masking). In experiment 1, MPPs were measured for lis teners with normal hearing using different masker levels. Carrier frequenci es of 3 and 6 kHz were used for the masker. The probe had a frequency of 6 kHz. For all masker levels, the off-frequency MPPs exhibited;deeper and lon ger valleys compared with the on-frequency MPPs. Hearing-impaired listeners were tested in experiment 2. For some hearing-impaired subjects, masker fr equencies of 1.5 kHz and 3 kHz were paired with a probe frequency of 3 kHz. MPPs measured for listeners with hearing loss had similar shapes for on- a nd off-frequency maskers. It was hypothesized that the shapes of MPPs refle ct nonlinear processing at the level of the basilar membrane in normal hear ing and more linear processing in impaired hearing. A model assuming differ ent cochlear gains for normal versus impaired hearing and similar parameter s of the temporal integrator for both groups of listeners successfully pred icted the MPPs. (C) 2001 Acoustical Society of America.