Absence of effect of coherent frequency modulation on grouping a mistuned harmonic with a vowel

When a single harmonic close to the first formant frequency is mistuned by about 8%, that harmonic makes a reduced contribution to the vowel's first formant frequency as measured by a shift in the phoneme boundary along an F1 continuum between /I/ and /epsilon/ [C.J. Darwin and R.B Gardner, J. Acoust. Soc. Am. 79, 838-45 (1986)]. In the present experiments, phoneme boundaries along an /I/-/epsilon/ continuum were measured for vowels differing in F1 whose fourth harmonic (500 Hz) was mistuned by 0, +/- 3, +/- 6, or +/- 9%. All the harmonics of a vowel (including the mistuned one) were given either no FM or coherent FM at a rate of 6 Hz and modulation depth of +/- 5%. The results replicated the previous findings, but found no evidence for coherent FM preventing the segregation of the mistuned harmonic from the vowel.