ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06
2pPP31. Forward-masked intensity discrimination: Duration effects.
Robert S. Schlauch
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.]