Abstract:

Detection thresholds for a tone in an unfamiliar tonal pattern can be greatly elevated under conditions of masker uncertainty [E. Oh and R. A. Lutfi, J. Acoust. Soc. Am. 101, 3148 (1997)]. Two experiments were conducted to determine whether harmonicity and onset/offset synchrony of masker tones can reduce the detrimental effect of masker uncertainty. Masker uncertainty was introduced by randomly varying the frequencies and amplitudes of masker tones on each presentation. In experiment 1, maskers were composed of 2--49 tones that were multiples of 200 Hz, not including 1000 Hz. Anywhere from 2--10 dB less masking was observed for an inharmonically related signal at 1047 Hz than for a harmonic signal at 1000 Hz. In experiment 2, the onsets and offsets of masker tones covaried or varied independently of each other. As much as 30 dB less masking was obtained for the 1000-Hz tone signal when masker tones covaried in time. The results support the idea that harmonicity and onset/offset synchrony cause the signal to be perceptually segregated from the masker, thereby resulting in less masking.