Syllable affiliation of final consonant clusters undergoes a phase transition over speaking rates

Previous work (B. Tuller and J.A.S. Kelso, 1990) reported a change in syllable affiliation, which was reflected by a change in the relative phase of glottal and lip movements, as the rate of speaking a VC syllable increased. That is /ip#ip#.../ becomes /pi#pi#.../ as speaking rate is systematically increased. We report a change in the syllable affiliation of part of a final consonant cluster; /opt#opt#.../ becomes /top#top#.../ at higher speaking rates. The relative phase between the time series generated by two supralaryngeal structures, the lip and tongue tip, was measured in three ways: discrete Fourier transform, cospectrum, and dynamic time warping. Speaking rate was controlled using a metronome that began at 1 Hz and increased to 3.25 Hz in 0.083 Hz steps every 12 repetitions. Subjects repeated the target word "opt" "hopped," or "top" in time with the metronome while movements of their tongue, tongue blade, lower lip, and jaw were tracked by an alternating magnetic field device, the Articulograph AG100. Phonetic analysis confirmed the presence of a transition from VCC to CVC syllabic at higher speaking rates. The perceptual change corresponds to a statistically significant change in the measurements of relative phase, indicating that perceived syllable affiliation is determined, to some extent by relative timing of articulatory events. This effect is consistent across the five subjects. Three methods of measuring relative timing are compared, and the theoretical issues behind these methods are discussed.