Backward Masking of Short Tones by Narrow- and Wide-Band Noise Bursts

Abstract

Onset of a 10-msec tone (one of 11 frequencies from 250 to 4000 cps) preceded onset of a 100-msec, 70-dB-SPL noise burst (wide band or 200 cps centered at 1270 cps) by 100, 50, 35, 20, 15, and 10 msec. Masked tonal thresholds, obtained by a method of adjustment, were evaluated relative to tone thresholds in quiet and in continuous noise of equal spectra. At the longest time interval (Δt=−100 msec), both noises produced equal backward masking at all frequencies. For the wide-band masker, “backward overshoot,” a corollary to Zwicker's simultaneous phenomenon and defined as the pure-tone backward-masked threshold minus the threshold for continuous masking, was greatest at higher frequencies and occurred for intervals as long as Δt=−20 msec. The narrow-band noise produced masking for frequencies within the band at Δt=−50 msec and considerable threshold shift for these same frequencies at briefer time intervals. Backward overshoot was pronounced for frequencies above and below the narrow band, extending back to intervals of Δt=−50 msec, but was small for within-band frequencies (compared to the relatively great threshold elevation for the continuous masking). Results are interpreted in terms of temporal development of the critical band. [Supported by the National Institute of Nervous Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]