Stephen Tobin

Timing effects of syllable structure and stress on nasals: a real-time MRI examination.

The coordination of velum and oral gestures for English [n] is studied using real-time MRI movies to reconstruct vocal tract aperture functions. This technique allows for the examination of parts of the vocal tract otherwise inaccessible to dynamic imaging or movement tracking. The present experiment considers syllable onset, coda, and juncture geminate nasals and also addresses the effects of a variety of word stress patterns on segment internal coordination. We find a bimodal timing pattern in which near-synchrony of velum lowering and tongue tip raising characterizes the timing for onsets and temporal lag between the gestures is characteristic for codas, supporting and extending the findings of Krakow (1989), 1993) for [m]. Intervocalic word-internal nasals are found to have timing patterns that are sensitive to the local stress context, which suggests the presence of an underlying timing specification that can yield flexibly. We consider these findings in light of the gestural coupling structures described by Goldstein and colleagues (Goldstein, Byrd, & Saltzman 2006; Nam, Goldstein, and Saltzman in press; Goldstein, Nam, Saltzman, & Chitoran 2008).

Syllable structure effects on velum‐oral coordination evaluated with real‐time MRI

Seminal work by Krakow (PhD. Diss., Yale University, 1989, Phonetics and Phonology 5, 87–116, 1993) has indicated that intrasegmental coordination of articulatory gestures varies systematically as a function of syllable position. Specifically, onset and coda nasals display different lag times between the velum and oral gestural components. In onset nasals, velum lowering is achieved roughly synchronously with oral constriction, while in codas, velum lowering precedes oral constriction. However, Krakow’s study was limited by its reliance on indirect measures of velum movement. Nor did her work examine nasals other than [m] or syllable organizations other than singleton onsets and codas. Our study employs real‐time magnetic resonance imaging [Narayanan et al., J. Acoust. Soc. Am. 115, 1771–1776 (2004); Mathiak et al., Int. J. of Lang. & Comm. Disorders 35, 419–425 (2000)] to acquire direct information about the key vocal tract variables of velum aperture and oral constriction, thereby allowing the calculati...

Resonance tuning in soprano singing and vocal tract shaping: Comparison of sung and spoken vowels

Singing at high pitches by sopranos involves complex orchestration of vocal‐fold mechanisms and vocal‐tract shaping. A specific phenomenon is the tuning of vocal‐tract resonances to the fundamental at high pitches. Measurement of vocal‐tract resonances has shown that this is particularly true for the first resonance [Joliveau et al. (2004)]. Higher resonances show some increase in their values perhaps reflecting incidental effects rather than active tuning. We investigate vocal‐tract shaping in soprano singing using a real‐time MRI technique [Narayanan et al. (2004)] with synchronized noise‐cancelled audio recording. A professionally trained Western‐classical singer spoke and sang the vowels /a, i, u, o, e/ preceded by the consonant /l/ over an ascending scale (from B‐flat below middle C, rising two octaves). Acoustic analysis shows clear evidence of F1 tuning to F0 in the higher‐octave singing of the vowels. The vocal‐tract shape was distinctly different at the higher pitches compared to vowels spoken at...

Phonetic accommodation in Spanish-English and Korean-English bilinguals

Preliminary results from a cross-linguistic investigation of phonetic accommodation in speech production and perception are presented. The finding that synchronous actions are more stable than asynchronous ones has been reported in studies of general (Kelso, 1981) and speech-specific (Browman & Goldstein, 1992; Byrd, Tobin, Bresch & Narayanan, 2009) motor control. With reference to glottal-oral timing, near-zero VOTs (voice onset times) are representative of near-synchronous timing, whereas long-lag VOTs are representative of asynchronous timing (Sawashima & Hirose, 1980; Dixit, 1984; Lofqvist & Yoshioka, 1989; Fuchs, 2005). These observations served as a basis for the prediction that native speakers of Korean, with its long-lag aspirated stops (~120 ms), would more readily accommodate to typical English voiceless stop VOT (~70 ms) than native speakers of Spanish, with its short-lag voiceless stops (~20 ms). Spanish-English and Korean-English bilinguals were recorded reading voiceless stop-initial English words, before and during a task in which participants shadowed recorded productions of a native speaker of American English. Preliminary analysis of the production data provides some support for these hypotheses. The results contribute to our understanding of the conditions that promote phonetic accommodation.

A landmark-based approach to automatic voice onset time estimation in stop-vowel sequences

In the field of phonetics, voice onset time (VOT) is a major parameter of human speech defining linguistic contrasts in voicing. In this article, a landmark-based method of automatic VOT estimation in acoustic signals is presented. The proposed technique is based on a combination of two landmark detection procedures for release burst onset and glottal activity detection. Robust release burst detection is achieved by the use of a plosion index measure. Voice onset and offset landmarks are determined using peak detection on power rate-of-rise. The proposed system for VOT estimation was tested on two voiceless-stop-vowel combinations /ka/, /ta/ spoken by 42 native German speakers.

Assessing the effect of phonetic distance on accommodation

In investigations of phonetic accommodation, convergence is the most frequently reported finding (e.g., Babel, 2012). However, divergence is also attested under some circumstances (Giles, Coupland & Coupland 1991). On the basis of observations and modeling of Tobin and Nam (2009), Tobin, Nam and Fowler (under review) and Kopecz and Schoner (1995), we asked whether and how phonetic distance along some relevant phonetic dimension would modulate accommodation. Following Roon and Gafos (2014) and Gallantucci, Fowler and Goldstein (2009), who report systematic perceptuomotor effects in speech, we used a cue-distractor paradigm to assess the effect of distance. Participants were visually cued to produce a syllable (ta or ka). 150 ms later they heard a distractor syllable from a 5-step ta or ka VOT-continuum. Participants were assigned continua either near or distant from their baseline VOT. An ordinal logistic regression of data from 12 participants in the near condition indicated patterns of divergence from th...

Gestural drift in Serbian‐English speakers.

Following Tobin [J. Acoust. Soc. Am. 125, 2757 (2009)], perceptually guided changes in speech production were examined in a group of Serbian‐English speakers. Participants were recorded producing Serbian and English sentences after periods of time in the US and in Serbia. Voice onset times (VOTs) and vowel formants were examined with the aim of determining whether gestural targets as well as patterns of gestural timing are affected by exposure to a language. It is predicted that in both Serbian and English, VOTs will be longer after time in the US and shorter after time in Serbia. Based on comparisons of available American English and Serbian vowel formant data, it is expected that F1’s will increase and F2’s will decrease after time in Serbia while F1’s will decrease and F2’s will increase after time in the US. The results will be compared with those of Tobin’s Spanish‐English speakers and discussed with relation to recent research on phonetic convergence, attunement, and articulatory setting.