ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pPP31. Forward-masked intensity discrimination: Duration effects.

Robert S. Schlauch

Nicole Lanthier

Dept. of Commun. Disorders, 115 Shevlin Hall, Univ. of Minnesota, Minneapolis, MN 55455

Forward-masked intensity discrimination shows elevated just-noticeable differences (jnd's), for mid-level standards, a finding argued to be consistent with sensory adaptation [F. Zeng and C. W. Turner, 782--787 (1992)]. Accordingly, the size of jnd's should increase with increases in masker duration. We tested this notion by measuring forward-masked jnd's as a function of level for 1000-Hz tones in four listeners with normal hearing. Jnd's were measured for 10-ms standards in quiet and in the presence of a 1000-Hz masker with either a 10-ms or a 250-ms duration. The masker level was fixed at 90 dB SPL and the interval between masker offset and standard onset was 100 ms. Forced-choice procedures were employed. The results show significantly less masking for the longer duration masker (250 ms) than for the short one (10 ms). These results are contrary to the results reported for forward-masked detection. Listening bands revealed by measuring jnd's as a function of masker frequency suggest that off-frequency listening may be responsible for this finding [Work supported by the Bryng Bryngelson Fund.]