ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2pPP10. Effects of rise/fall time on masked detection thresholds and temporal integration for noise band signals.

M. G. Heinz

Dept. of Elec. and Comput. Eng., Johns Hopkins Univ., Baltimore, MD 21218

C. Formby

Univ. of Maryland School of Medicine, Baltimore, MD 21201

K. L. Mortimer

Georgetown Univ., Washington, DC 20057

Formby et al. [J. Acoust. Soc. Am. 96, 102--114 (1994)] noted that masked detection thresholds (MDT) and temporal integration (TI) for brief noise band signals may be influenced by the rise/fall time (RFT) used to gate the signals. Also, the definition of signal duration (T), defined (1) exclusive of RFT or (2) inclusive of RFT, affected time constant ((tau)) estimates for TI. In this study, the role of RFT was evaluated systematically for signal bandwidth (W=62--6000 Hz) and masker conditions reported by Formby et al. The MDTs were measured for a range of rise/fall time (RFT=1--40 ms) and plateau (P=1--20 ms) values to extend Formby et al.'s original durations (T=P=10--480 ms). In general, for a given W and P condition, MDT decreased and became asymptotic with increasing RFT. For a given W, the effect of RFT increased as P decreased, and the effect was greatest for small W. For P(greater than or equal to)10 ms and RFT(greater than or equal to)1 ms, MDTs were independent of RFT for all W. For T defined exclusive of RFT (i.e., T=P), (tau) was inversely proportional to RFT for W(less than or equal to)1000 Hz and invariant with RFT for W>1000 Hz. For T defined inclusive of RFT (i.e., T=2*RFT+P), (tau) increased monotonically with RFT for all W. [Research supported by NIH.]