Short-term temporal integration: Evidence for the influence of peripheral compression

Thresholds for a 6.5-kHz sinusoidal signal, temporally centered in a 400-ms broadband-noise masker, were measured as a function of signal duration for normally hearing listeners and listeners with cochlear hearing loss over a range of masker levels. For the normally hearing listeners, the slope of the function relating signal threshold to signal duration (integration function) was steeper at medium masker levels than at low or high levels by a factor of nearly 2, for signal durations between 2 and 10 ms, while no significant effect of level was found for signal durations of 20 ms and more. No effect of stimulus level was found for the hearing-impaired listeners at any signal duration. For signal durations greater than 10 ms, consistent with many previous studies, the slope of the integration function was shallower for the hearing-impaired listeners than for the normally hearing listeners. However, for shorter durations, there was no significant difference in slope between the results from the hearing-impaired listeners and those from the normally hearing listeners in the high- and low-level masker conditions. A model incorporating a compressive nonlinearity, representing the effect of basilar-membrane (BM) compression, and a short-term temporal integrator, postulated to be a more central process, can account well for changes in the short-term integration function with level, if it is assumed that the compression is greater at medium levels than at low or high levels by a factor of about 4. This is in reasonable agreement with physiological measurements of BM compression, and with previous psychophysical estimates.