Abstract:

Recent experiments [S. Furukawa and B. C. J. Moore, J. Acoust. Soc. Am. 101, 1632--1643 (1997)] indicate that listeners are better at detecting coherent than incoherent FM imposed on two widely separated frequency components. Experiment 1 repeated one of these experiments using carrier frequencies of 1100 Hz and 1925 Hz, modulated by one cycle of a 2.5-Hz sinusoid, in a noise background. Four out of eight listeners showed superior detection for coherent than for incoherent FM. Experiment 2 investigated whether this superiority was due to coherent FM producing larger changes in virtual pitch than does incoherent FM, despite the inharmonic ratio between the two components. In the signal interval of a 3I,2AFC task, the carrier frequencies of 1100 and 1925 Hz were shifted in either the same or in opposite directions, without disrupting the pattern of FM, which was either coherent, incoherent, or absent. Whatever the pattern of modulation, sensitivity was better for ``same direction'' than for ``opposite direction'' shifts, a result consistent with sensitivity to changes in virtual pitch. It is concluded that virtual phase sensitivity may account for the superior detection of coherently modulated tones, without recourse to an across-frequency mechanism specific to FM coherence.