A new procedure for measuring peripheral compression in normal-hearing andhearing-impaired listeners

Forward-masking growth functions for on-frequency (6-kHz) and off-frequency (3-kHz) sinusoidal maskers were measured in quiet and in a high-pass noise just above the 6-kHz probe frequency. The data show that estimates of resp onse-growth rates obtained from those functions in quiet, which have been u sed to infer cochlear compression, are strongly dependent on the spread of probe excitation toward higher frequency regions. Therefore, an alternative procedure for measuring response-growth rates was proposed, one that emplo ys a fixed low-level probe and avoids level-dependent spread of probe excit ation. Fixed-probe-level temporal masking curves (TMCs) were obtained from normal-hearing listeners at a test frequency of 1 kHz, where the short 1-kH z probe was fixed in level at about 10 dB SL. The level of the preceding fo rward masker was adjusted to obtain masked threshold as a function of the t ime delay between masker and probe. The TMCs were obtained for an on-freque ncy masker (I kHz) and for other maskers with frequencies both below and ab ove the probe frequency. From these measurements, input/output response-gro wth curves were derived for individual ears. Response-growth slopes varied from > 1.0, at low masker levels to <0.2 at mid masker levels. In three sub jects, response growth increased again at high masker levels (> 80 dB SPL). For the fixed-level probe, the TMC slopes changed very little in the prese nce of a high-pass noise masking upward spread of probe excitation. A great er effect on the TMCs was observed when a high-frequency cueing tone was us ed with the masking tone. In both cases, however, the net effects on the es timated rate of response growth were minimal. (C) 2001 Acoustical Society o f America.