Adamantios I. Gafos

A Grammar of Gestural Coordination

Linguistic form is expressed in space, as articulators effectconstrictions at various points in the vocal tract, but also in time, as articulators move. A rather widespread assumption in theories of phonology and phonetics is that the temporal dimension of speech is largely irrelevant to the description and explanation of the higher-level or more qualitative aspects of sound patterns. The argument is presented that any theory of phonology must include a notion of temporal coordination of gestures. Linguistic grammars are constructed in part out of this temporal substance. Language-particular sound patterns are in part patterns of temporal coordination among gestures.1

Dynamics of phonological cognition.

A fundamental problem in spoken language is the duality between the continuous aspects of phonetic performance and the discrete aspects of phonological competence. We study 2 instances of this problem from the phenomenon of voicing neutralization and vowel harmony. In each case, we present a model where the experimentally observed continuous distinctions are linked to the discreteness of phonological form using the mathematics of nonlinear dynamics.

Syllabification in Moroccan Arabic : evidence from patterns of temporal stability in articulation

Competing proposals on the syllabification of initial consonants in Moroccan Arabic are evaluated using a combination of experimental and modelling techniques. The proposed model interprets an input syllable structure as a set of articulatory landmarks coordinated in time. This enables the simulation of temporal patterns associated with the input syllable structure under different noise conditions. Patterns of stability between landmarks simulated by the model are matched to patterns in data collected with Electromagnetic Articulometry experiments. The results implicate a heterosyllabic parse of initial clusters so that strings like /sbu/ comprise two syllables, [s.bu]. Beyond this specific result for Moroccan Arabic, the model reveals the range of validity of certain stability-based indexes of syllable structure and generates predictions that allow evaluation of a syllabic parse even when stability-based heuristics break down. Overall, the paper provides support for the broad hypothesis that syllable structure is reflected in patterns of temporal stability and contributes analytical tools to evaluate competing theories on the basis of these patterns.

Dynamic invariance in the phonetic expression of syllable structure : a case study of Moroccan Arabic consonant clusters*

We asked whether invariant phonetic indices for syllable structure can be identified in a language where word-initial consonant clusters, regardless of their sonority profile, are claimed to be parsed heterosyllabically. Four speakers of Moroccan Arabic were recorded, using Electromagnetic Articulography. Pursuing previous work, we employed temporal diagnostics for syllable structure, consisting of static correspondences between any given phonological organisation and its presumed phonetic indices. We show that such correspondences offer only a partial understanding of the relation between syllabic organisation and continuous indices of that organisation. We analyse the failure of the diagnostics and put forth a new approach in which different phonological organisations prescribe different ways in which phonetic indices change as phonetic parameters are scaled. The main finding is that invariance is found in these patterns of change, rather than in static correspondences between phonological constructs and fixed values for their phonetic indices.

Perceptuo-motor effects of response-distractor compatibility in speech: beyond phonemic identity

Previous studies have found faster response times in a production task when a speaker perceives a distractor syllable that is identical to the syllable they are required to produce. No study has found such effects when a response and a distractor are not identical but share parameters below the level of the phoneme. Results from Experiment 1 show some evidence of a response-time effect of response-distractor voicing congruency. Experiment 2 showed a robust effect of articulator congruency: perceiving a distractor that has the same articulatory organ as that implicated in the planned motor response speeds up response times. These results necessitate a more direct and specific formulation of the perception-production link than warranted by previous experimental evidence. Implications for theories of speech production are also discussed.

Stochastic time models of syllable structure.

Drawing on phonology research within the generative linguistics tradition, stochastic methods, and notions from complex systems, we develop a modelling paradigm linking phonological structure, expressed in terms of syllables, to speech movement data acquired with 3D electromagnetic articulography and X-ray microbeam methods. The essential variable in the models is syllable structure. When mapped to discrete coordination topologies, syllabic organization imposes systematic patterns of variability on the temporal dynamics of speech articulation. We simulated these dynamics under different syllabic parses and evaluated simulations against experimental data from Arabic and English, two languages claimed to parse similar strings of segments into different syllabic structures. Model simulations replicated several key experimental results, including the fallibility of past phonetic heuristics for syllable structure, and exposed the range of conditions under which such heuristics remain valid. More importantly, the modelling approach consistently diagnosed syllable structure proving resilient to multiple sources of variability in experimental data including measurement variability, speaker variability, and contextual variability. Prospects for extensions of our modelling paradigm to acoustic data are also discussed.

Stochastic time analysis of syllable-referential intervals and simplex onsets

Abstract We pursue an analysis of the relation between qualitative syllable parses and their quantitative phonetic consequences. To do this, we express the statistics of a symbolic organization corresponding to a syllable parse in terms of continuous phonetic parameters which quantify the timing of the consonants and vowels that make up syllables: consonantal plateau durations, vowel durations, and their variances. These parameters can be estimated from continuous phonetic data. This enables analysis of the link between symbolic phonological form and the continuous phonetics in which this form is manifest. Pursuing such an analysis, we illustrate the predictions of the syllabic organization corresponding to simplex onsets and derive a number of previously experimentally observed and simulation results. Specifically, we derive not only the canonical phonetic manifestations of simplex onsets but also the result that, under certain conditions we make precise, the phonetic indices of the simplex onset organization change to a range of values characteristic of the complex onset organization. Finally, we explore the behavior of phonetic indices for syllabic organization over progressively increasing sizes of lexical samples, thereby concomitantly diversifying the phonetic context over which these indices are taken.

Timing of German onset and word boundary clusters

Abstract Previous studies suggest that there are special timing relations in syllable onsets. The consonants are assumed to be timed, on the one hand, with the vocalic nucleus and, on the other hand, with each other. These competing timing relations result in the C-center effect. However, the C-center effect has not consistently been found in languages with complex onsets. Moreover, it has occasionally been found in languages disallowing complex onsets. The present study investigates onset timing in German while discussing alternative explanations (not related to bonding) for the timing patterns observed. Six German speakers were recorded via Electromagnetic Articulography. The corpus contained items with four clusters (/sk/, /kv/, /gl/, and /pl/). The clusters occur in word-initial position, word-medial position, and across a word boundary preceding different vowels. The results suggest that segmental properties (i.e., oral-laryngeal coordination, coarticulatory resistance) determine the observed timing patterns, and specifically the absence or presence of the C-center effect.

The Gesture as an Autonomous Nonlinear Dynamical System

ABSTRACT We propose a theory of how the speech gesture determines change in a functionally relevant variable of vocal tract state (e.g., constriction degree). A core postulate of the theory is that the gesture determines how the variable evolves in time independent of any executive timekeeper. That is, the theory involves intrinsic timing of speech gestures. We compare the theory against others in which an executive timekeeper determines change in vocal tract state. Theories that employ an executive timekeeper have been proposed to correct for disparities between theoretically predicted and experimentally observed velocity profiles. Such theories of extrinsic timing make the gesture a nonautonomous dynamical system. For a nonautonomous dynamical system, the change in state depends not just on the state but also on time. We show that this nonautonomous extension makes surprisingly weak kinematic predictions both qualitatively and quantitatively. We propose instead that the gesture is a theoretically simpler nonlinear autonomous dynamical system. For the proposed nonlinear autonomous dynamical system, the change in state depends nonlinearly on the state and does not depend on time. This new theory provides formal expression to the notion of intrinsic timing. Furthermore, it predicts experimentally observed relations among kinematic variables.

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.