Karen B. Snell
Dept. of Audiol., Rochester Inst. of Technol., 52 Lomb Memorial Dr., Rochester, NY 14623-5604
Smith College, Northampton, MA 01060
The detectability of a masked sinusoid increases as its onset approaches the temporal center of a masker. This study was designed to determine whether a similar change in detectability would occur for a silent gap as its onset was parametrically displaced from the onset of a noise burst. Gap thresholds were obtained for four subjects. Signals were 150-ms, 6-kHz low-passed noise bursts presented at an overall level of 75 dB SPL. A 10-ms cosine-squared envelope shaped the onset and offset of the noise burst. Gaps were shaped by a 1-ms cosine-squared envelope. Gaps onsets were displaced by 0, 1, 3, 5, 10, 30, 50, 100, 110, and 120 ms. The displacement was measured from the first point of full amplitude following the 10-ms shaped onset. Gap thresholds were determined in a 3IFC procedure using 75-trial runs. Subjects completed five replications without prior practice. The mean gap threshold was largest for the noise burst closest to signal onset (5.67 ms) and smallest for the gap offset by 60 ms from the signal onset (2.01 ms). For all subjects, gap thresholds decreased as the gap approached the noise burst center.