ASA 125th Meeting Ottawa 1993 May

2pPP14. Detection of amplitude modulation with linear-frequency-modulated carriers.

James W. Pitton

Dept. Elec. Eng. FT-10, Univ. of Washington, Seattle, WA 98195

Edward M. Burns

Les E. Atlas

Univ. of Washington, Seattle, WA 98195

Results are presented for detection of sinusoidal amplitude modulation (AM) superimposed upon linear-frequency-modulated, 120-ms tone bursts. Thresholds for detection of AM were obtained using an adaptive 2IFC procedure over a range of AM frequencies from 25 to 400 Hz, and over a range of frequency modulation (FM) rates from 0 to 30 Hz/ms. The stimuli are a simplification of speech transitions, with both AM and FM, but consisting of only one signal component. These experiments explore the ability to detect modulations that are distributed across critical bands. For fast rates of FM, the stimuli will sweep through a critical band within one to two periods of the AM. A rapid frequency transition also broadens the spectrum of the signal, so that these stimuli do not possess the distinct sidebands of an amplitude-modulated, stationary tone. Thus, both temporal cues from periodicities within individual channels and place cues derived from the excitation pattern will weaken as the FM rate increases. Nonetheless, data indicate that listeners readily detect amplitude modulation for all modulation frequencies at the highest rates of FM. These data will be discussed in light of some current physiologically based models of auditory processing, wherein both within- and across-channel temporal information is utilized. [Work supported by the Virginia Merrill Bloedel Hearing Research Center, University of Washington.]