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

3aPP9. Detection of decrements and increments in sinusoids at high overall levels.

Brian C. J. Moore

Dept. of Exp. Psych., Univ. of Cambridge, Downing St., Cambridge CB2 3EB, England

Robert W. Peters

Univ. of North Carolina, Chapel Hill, NC 27599-7190

Brian R. Glasberg

Univ. of Cambridge, Cambridge, England

Thresholds for the detection of decrements in level of sinusoidal signals were measured as a function of duration (2, 4, 6, 10, and 14 ms), level (70, 80, and 90 dB SPL) and frequency (250, 500, 1000, 2000, and 4000 Hz). Seven normally hearing listeners were tested at each frequency. Thresholds for detecting a 10-ms increment in level were also measured. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the decrement or increment. Performance improved with increasing frequency for all decrement and increment durations. Performance also tended to improve with increasing level at 2000 and 4000 Hz. The results were analyzed using a four-stage model consisting of an auditory filter, a nonlinearity, a sliding temporal integrator, and a decision mechanism. The analysis indicated that the improved performance with increasing frequency and increasing level can be attributed mainly to changes in the detection process following the temporal integrator rather than changes in the equivalent rectangular duration (ERD) of the temporal integrator. The ERD varied little with changes in frequency and level. At higher frequencies and levels a smaller change is required at the output of the integrator for threshold to be reached.