The influence of extraneous sounds on the perceptual estimation of first-formant frequency in vowels under conditions of asynchrony

Abstract

The presence of an extraneous sound in the first formant (F1) region of a voiced vowel has been shown to influence its perceived phonetic quality when the vowel and the extraneous sound begin and end in synchrony. These experiments examine whether this effect, produced here by a pair of extraneous tones not harmonically related to the vowel’s fundamental frequency, depends on the degree of synchrony of the vowel and the tones. The phonetic effects of the tones were measured as a change in the position of the phoneme boundary on a continuum of vowels, perceived as changing from /ɪ/ to /ɛ/ as F1 was increased. Experiment 1 demonstrated that the boundary shift resulting from the addition of the tones declined when the tones began prior to the vowel. This effect might be due to adaptation or to perceptual grouping. In experiment 2, a sequence of “captor” tones was used in an attempt to reinstate the phonetic effects of these tones, by “grouping out” the portions that were not simultaneous with the vowel. This did not provide any evidence for perceptual grouping. Experiment 3 demonstrated that offset asynchronies could also reduce the phonetic effects of the extraneous tones, although not to the same extent as could onset asynchronies. This indicated that perceptual grouping mechanisms were at least partly responsible for the effects of asynchronies. The boundary shift induced by the extraneous tones was significant even for the longest onset and offset asynchronies used, indicating that the phonetic effects of these tones are not limited to cases where vowels and tones are precisely synchronized.