Elizabeth A. Strickland
Neal F. Viemeister
Dept. of Psychol., Univ. of Minnesota, 75 E. River Rd., Minneapolis, MN 55455
In a previous paper, detection thresholds for amplitude modulation at a ``signal'' modulation frequency (4, 16, 100, and 400 Hz) in the presence of a ``masker'' modulation frequency (2 to 800 Hz) were presented, when the carrier was a broadband noise [Strickland and Viemeister, J. Acoust. Soc. Am. Suppl. 1 86, S11 (1989)]. Broad tuning for modulation frequency was found, and for maskers half or twice the signal modulation frequency, threshold depended on the relative phases of the signal and masker modulators. Although this tuning has been taken as evidence for ``channels'' for modulation frequency, phase effects would not be predicted by such a mechanism. In the present study these results were used to determine what aspects of envelopes listeners might use in making decisions. Simulations were performed using the envelope detector model (bandpass filtering, half-wave rectification, and low-pass filtering) with decisions based on envelope statistics that have been used to predict other data. These statistics were (1) rms power, (2) ratio of maximum to minimum amplitude (max/min), (3) crest factor, (4) fourth moment, and (5) average slope. The max/min statistic was successful at predicting the major trends in the data, including tuning, without requiring the presence of modulation frequency channels. [Work supported by NIDCD Grant No. DC00110.]