ASA 127th Meeting M.I.T. 1994 June 6-10

4aPP19. Masking of a short probe by sinusoidal FM.

Brent W. Edwards

Neal F. Viemeister

Dept. of Psychol., Univ. of Minnesota, 75 East River Rd., Minneapolis MN 55455

In experiment I, a 10-ms, 1-kHz probe was detected in the presence of an FM masker centered at 1 kHz and sinusoidally modulated at 16 Hz. The probe was presented when the instantaneous frequency of the masker was 1 kHz. As the modulation index ((beta)) of the masker was increased---increasing the frequency excursion and decreasing the energy of the masker near 1 kHz---the detection threshold of the probe increased by as much as 20 dB. This result is contrary to predictions based on simple energy detection. Since both the sweep rate and frequency excursion of the masker increase as (beta) increases, frequency-clipped FM maskers were used in experiment II to fix either rate or excursion. Thresholds agreed with the data from experiment I for equal excursions but not equal rates. In experiment III, the maskers from the first two experiments were passed through a roex filter centered at 1 kHz and the resulting envelope was used to amplitude-modulate a 1-kHz tone. This AM signal was used as the masker. Probe detection thresholds varied as a function of (beta), excursion and rate in the same manner as they did with the FM maskers in experiments I and II. [Work supported by NIDCD DC00683.]