Perceptual grouping of formants with static and dynamic differences in fundamental frequency

The perceptual consequences of exciting one formant (F2 or F4) of a composite syllable with a different fundamental from the others were examined in experiment 1 using a four-formant syllable for which F1, F2, and F3 give /ru/ and F1, F3, and F4 give /li/. When all four formants are on the same fundamental, the percept is /ru/, but exciting F2 on a sufficiently different fundamental gave predominantly /li/ percepts. Smaller differences in fundamental left the phonetic percept unchanged but made F2 stand out as a separate sound source. Exciting F4 on a different fundamental also made it stand out as a separate sound source, though larger differences in fundamental were needed than for F2. Experiment 2 replicated these static effects of fundamental frequency differences on F2, but failed to find any substantial effect of coherent or incoherent fundamental frequency modulation functions on perceptual grouping or separation. Although static differences in fundamental frequency exert a strong effect on the perceptual grouping of formants both in terms of the number of sound sources heard and the perceived phonetic category, the coherence of fundamental frequency movement has almost no independent effect on the perceptual grouping of formants.