ASA 126th Meeting Denver 1993 October 4-8

2aPP5. Some effects of modulator phase on the detection of a signal in a sinusoidally amplitude-modulated tonal complex.

Michelle L. Hicks Sid P. Bacon

Psychoacoust. Lab., Dept. of Speech and Hear. Science, Arizona State Univ., Tempe, AZ 85287-1908

Subjects were required to detect a 1000-Hz signal in the presence of a masker that consisted of a 1000-Hz (on-frequency) component alone or that component and six flanking components (500, 600, 700, 1300, 1400, and 1500 Hz). The on-frequency component typically was sinusoidally amplitude modulated at 10 Hz and the signal was presented in a dip in the envelope of the on-frequency component or in three successive dips. In experiment 1, the flanking components could lower (comodulation masking release or CMR) or elevate (across-channel masking or ACM) threshold, depending upon whether they were modulated in phase with the on-frequency component, or staggered in phase. CMR was observed for both signal types, although it was smaller for the three-burst signal. ACM was only observed for the three-burst signal. These differences were primarily due to lower thresholds in the presence of the on-frequency component alone for the three-burst signal. In experiment 2, thresholds were measured as a function of the modulator phase of the flanking components. The on-frequency component was unmodulated or 100% amplitude modulated (modulator phase of 0(degrees)). For both monotic and dichotic presentations of the flanking components, thresholds increased and then decreased as the modulator phase of the flanking components varied together from 0 to 360(degrees). [Work supported by NIDCD.]