SPREAD OF EXCITATION PRODUCED BY MASKERS WITH DAMPED AND RAMPED ENVELOPES

Three experiments compared the ability of pairs of modulated narrow-ba nd sounds with identical power spectra to mask signals above, below, a nd at their center frequency. In the first experiment, forward-masked psychophysical tuning curves (PTCs) were measured using a 1600-Hz 10-m s signal and 400-ms ''damped'' and ''ramped'' sinusoidal maskers, The damped maskers were produced by repeating a 25-ms sinusoid which had b een shaped by an exponentially decaying function with a half-life of 4 ms. The ramped maskers were simply time reversals of the damped maske rs. When the masker frequency was below that of the signal, ramped mas kers were more effective than damped maskers, whereas the reverse was true for maskers above the signal. Experiment 2 measured thresholds fo r a 400-ms 1000-Hz damped or ramped sinusoidal signal, in the presence of a simultaneous masker with the same envelope shape, as a function of the masker frequency. Again, ramped maskers were more effective bel ow the signal frequency, and damped maskers more effective above it. E xperiment 3 was similar to experiment 2 except that the masker was a d amped or ramped narrow-band noise, and the signal was an unmodulated s inusoid. The pattern of results was generally similar to that obtained in experiments 1 and 2. The results of all three experiments are inco nsistent with the ''traditional'' method of calculating excitation pat terns, which is based on the power spectrum of the stimulus, and also differ from the predictions of a recent model of auditory processing [ R. D. Patterson, J. Acoust. Sec. Am. 96, 1409-1418 (1994)]. It is sugg ested that changes to the peripheral filtering stage of Patterson's mo del may provide a useful first step toward accounting for the data. (C ) 1996 Acoustical Society of America.