Peripheral compression as a function of stimulus level and frequency region in normal-hearing listeners.

Fixed-probe-level temporal masking curves (TMCs) were obtained from normal-hearing listeners at probe frequencies between 250 and 8000 Hz. The short probe tones were fixed in level (approximately 10-dB SPL). The level of the preceding forward masker was adjusted to obtain masked threshold as a function of the time delay between masker and probe. These isoresponse TMCs were obtained for an on-frequency masker, where the masker frequency (Fm) and probe frequency (Fp) were the same, and for an off-frequency masker below the probe frequency (Fm = 0.6 Fp). Slopes of off-frequency TMCs for probe tones at 250-1000 Hz were steeper than those for probe tones between 2000 and 4000 Hz, supporting the notion that response growth for Fm = 0.6 Fp at lower probe frequencies is not linear. Therefore, a group average off-frequency TMC slope, for probe frequencies between 2 and 4 kHz, was used to calculate response growth at every probe frequency. Input/output response growth curves were derived from the TMCs, and response growth rates were calculated as a function of the masker level in individual ears. At any particular probe frequency, response growth rates varied with input level, from near 1.0 at low input levels, to <0.2 at mid levels, and back to near 1.0 at levels above 80-dB SPL. It was concluded that compression is equally strong at low and high frequencies as it is at mid frequencies.