ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3aPP1. Forward-masked intensity increment thresholds at two recovery times.

Lance Nizami

Bruce A. Schneider

Dept. of Psychol., Erindale College, Univ. of Toronto, 3359 Mississauga Rd., Mississauga, ON L5L 1C6, Canada

Forward-masked just-noticeable differences were obtained from two listeners using a two-interval forced-choice procedure. In one of the intervals, a 2-kHz, 200-ms masker preceded a 2-kHz Gaussian-shaped tone pip ((sigma)=0.5 ms). The other interval contained the same masker followed by a comparison tone pip. The listener's task was to identify the interval containing the louder tone pip. Within a block of trails both masker intensity (range =10--80 dB SPL) and masker-target time gap (3 or 80 ms) were kept constant. The intensity of the standard tone pip (before multiplication by the Gaussian envelope) was always set to 20 dB above the level of the masker. When intensity-increment thresholds are plotted as a function of masker level at both time gaps, thresholds rise to a maximum at a masker level of 50 dB SPL before declining again. This pattern may be consistent with the idea of two intensity-processing channels, one for louder sounds and one for softer ones [see F.-G. Zeng, C. W. Turner, and E. M. Relkin, Hear. Res. 55, 223--230 (1991)]. [Work supported by NSERC.]