Auditory normalization of French vowels synthesized by an articulatory model simulating growth from birth to adulthood

The present article aims at exploring the invariant parameters involved in the perceptual normalization of French vowels. A set of 490 stimuli, including the ten French vowels /i y u e ? o E oe (inverted c) a/ produced by an articulatory model, simulating seven growth stages and seven fundamental frequency values, has been submitted as a perceptual identification test to 43 subjects. The results confirm the important effect of the tonality distance between F1 and f0 in perceived height. It does not seem, however, that height perception involves a binary organization determined by the 3-3.5-Bark critical distance. Regarding place of articulation, the tonotopic distance between F1 and F2 appears to be the best predictor of the perceived front-back dimension. Nevertheless, the role of the difference between F2 and F3 remains important. Roundedness is also examined and correlated to the effective second formant, involving spectral integration of higher formants within the 3.5-Bark critical distance. The results shed light on the issue of perceptual invariance, and can be interpreted as perceptual constraints imposed on speech production.     

A study of high front vowels with articulatory data and acoustic simulations

The purpose of this study is to test a methodology for describing the articulation of vowels. High front vowels are a test case because some theories suggest that high front vowels have little cross-linguistic variation. Acoustic studies appear to show counterexamples to these predictions, but purely acoustic studies are difficult to interpret because of the many-to-one relation between articulation and acoustics. In this study, vocal tract dimensions, including constriction degree and position, are measured from cinéradiographic and x-ray data on high front vowels from three different languages (North American English, French, and Mandarin Chinese). Statistical comparisons find several significant articulatory differences between North American English /i/ and Mandarin Chinese and French /i/. In particular, differences in constriction degree were found, but not constriction position. Articulatory synthesis is used to model the acoustic consequences of some of the significant articulatory differences, finding that the articulatory differences may have the acoustic consequences of making the latter languages' /i/ perceptually sharper by shifting the frequencies of F(2) and F(3) upwards. In addition, the vowel /y/ has specific articulations that differ from those for /i/, including a wider tongue constriction, and substantially different acoustic sensitivity functions for F(2) and F(3).     

Coarticulatory influences on the perceived height of nasal vowels

Certain of the complex spectral effects of vowel nasalization bear a resemblance to the effects of modifying the tongue or jaw position with which the vowel is produced. Perceptual evidence suggests that listener misperceptions of nasal vowel height arise as a result of this resemblance. Whereas previous studies examined isolated nasal vowels, this research focused on the role of phonetic context in shaping listeners' judgments of nasal vowel height. Identification data obtained from native American English speakers indicated that nasal coupling does not necessarily lead to listener misperceptions of vowel quality when the vowel's nasality is coarticulatory in nature. The perceived height of contextually nasalized vowels (in a [bVnd] environment) did not differ from that of oral vowels (in a [bVd] environment) produced with the same tongue-jaw configuration. In contrast, corresponding noncontextually nasalized vowels (in a [bVd] environment) were perceived as lower in quality than vowels in the other two conditions. Presumably the listeners' lack of experience with distinctive vowel nasalization prompted them to resolve the spectral effects of noncontextual nasalization in terms of tongue or jaw height, rather than velic height. The implications of these findings with respect to sound changes affecting nasal vowel height are also discussed.     

The timing of articulatory gestures: evidence for relational invariants

In this article, we examine the effects of changing speaking rate and syllable stress on the space-time structure of articulatory gestures. Lip and jaw movements of four subjects were monitored during production of selected bisyllabic utterances in which stress and rate were orthogonally varied. Analysis of the relative timing of articulatory movements revealed that the time of onset of gestures specific to consonant articulation was tightly linked to the timing of gestures specific to the flanking vowels. The observed temporal stability was independent of large variations in displacement, duration, and velocity of individual gestures. The kinematic results are in close agreement with our previously reported EMG findings [B. Tuller et al., J. Exp. Psychol. 8, 460-472 (1982)] and together provide evidence for relational invariants in articulation.     

Modeling the perception of concurrent vowels: vowels with the same fundamental frequency

The ability of listeners to identify pairs of simultaneous synthetic vowels has been investigated in the first of a series of studies on the extraction of phonetic information from multiple-talker waveforms. Both members of the vowel pair had the same onset and offset times and a constant fundamental frequency of 100 Hz. Listeners identified both vowels with an accuracy significantly greater than chance. The pattern of correct responses and confusions was similar for vowels generated by (a) cascade formant synthesis and (b) additive harmonic synthesis that replaced each of the lowest three formants with a single pair of harmonics of equal amplitude. In order to choose an appropriate model for describing listeners' performance, four pattern-matching procedures were evaluated. Each predicted the probability that (i) any individual vowel would be selected as one of the two responses, and (ii) any pair of vowels would be selected. These probabilities were estimated from measures of the similarities of the auditory excitation patterns of the double vowels to those of single-vowel reference patterns. Up to 88% of the variance in individual responses and up to 67% of the variance in pairwise responses could be accounted for by procedures that highlighted spectral peaks and shoulders in the excitation pattern. Procedures that assigned uniform weight to all regions of the excitation pattern gave poorer predictions. These findings support the hypothesis that the auditory system pays particular attention to the frequencies of spectral peaks, and possibly also of shoulders, when identifying vowels. One virtue of this strategy is that the spectral peaks and shoulders can indicate the frequencies of formants when other aspects of spectral shape are obscured by competing sounds.     

Modeling the perception of concurrent vowels: vowels with different fundamental frequencies

If two vowels with different fundamental frequencies (fo's) are presented simultaneously and monaurally, listeners often hear two talkers producing different vowels on different pitches. This paper describes the evaluation of four computational models of the auditory and perceptual processes which may underlie this ability. Each model involves four stages: (i) frequency analysis using an "auditory" filter bank, (ii) determination of the pitches present in the stimulus, (iii) segregation of the competing speech sources by grouping energy associated with each pitch to create two derived spectral patterns, and (iv) classification of the derived spectral patterns to predict the probabilities of listeners' vowel-identification responses. The "place" models carry out the operations of pitch determination and spectral segregation by analyzing the distribution of rms levels across the channels of the filter bank. The "place-time" models carry out these operations by analyzing the periodicities in the waveforms in each channel. In their "linear" versions, the place and place-time models operate directly on the waveforms emerging from the filters. In their "nonlinear" versions, analogous operations are applied to the output of an additional stage which applied a compressive nonlinearity to the filtered waveforms. Compared to the other three models, the nonlinear place-time model provides the most accurate estimates of the fo's of paris of concurrent synthetic vowels and comes closest to predicting the identification responses of listeners to such stimuli. Although the model has several limitations, the results are compatible with the idea that a place-time analysis is used to segregate competing sound sources.     

Determination of velum opening for french nasal vowels by magnetic resonance imaging

MRI techniques have been used to describe velum opening of French vowels. Data based on 18 joined axial slices of 4 mm thickness were recorded with four subjects. Differences in velum opening are calculated from areas measured in the tract between the lowered velum and the back pharynx wall. Results show that for all subjects, the back vowel / / has the smallest opening, while some variations are observed for the other vowels.     

Prosodic strengthening and featural enhancement: evidence from acoustic and articulatory realizations of /a,i/ in English

In this study the effects of accent and prosodic boundaries on the production of English vowels (/a,i/), by concurrently examining acoustic vowel formants and articulatory maxima of the tongue, jaw, and lips obtained with EMA (Electromagnetic Articulography) are investigated. The results demonstrate that prosodic strengthening (due to accent and/or prosodic boundaries) has differential effects depending on the source of prominence (in accented syllables versus at edges of prosodic domains; domain initially versus domain finally). The results are interpreted in terms of how the prosodic strengthening is related to phonetic realization of vowel features. For example, when accented, /i/ was fronter in both acoustic and articulatory vowel spaces (enhancing [-back]), accompanied by an increase in both lip and jaw openings (enhancing sonority). By contrast, at edges of prosodic domains (especially domain-finally), /i/ was not necessarily fronter, but higher (enhancing [+high]), accompanied by an increase only in the lip (not jaw) opening. This suggests that the two aspects of prosodic structure (accent versus boundary) are differentiated by distinct phonetic patterns. Further, it implies that prosodic strengthening, though manifested in fine-grained phonetic details, is not simply a low-level phonetic event but a complex linguistic phenomenon, closely linked to the enhancement of phonological features and positional strength that may license phonological contrasts.     

Adaptive computation of articulatory parameters from the speech signal

An unconstrained optimization technique is used to find the values of parameters, of a combination of an articulatory and a vocal tract model, that minimize the difference between model spectra and natural speech spectra. The articulatory model is anatomically realistic and the vocal tract model is a "lossy" Webster equation for which a method of solution is given. For English vowels in the steady state, anatomically reasonable articulatory configurations whose corresponding spectra match those of human speech to within 2 dB have been computed in fewer than ten iterations. Results are also given which demonstrate a limited ability of the system to track the articulatory dynamics of voiced speech.     

Generation of the vocal tract spectrum from the underlying articulatory mechanism

A method for synthesizing vocal-tract spectra from phoneme sequences by mimicking the speech production process of humans is presented. The model consists of four main processes and is particularly characterized by an adaptive formation of articulatory movements. First, our model determines the time when each phoneme is articulated. Next, it generates articulatory constraints that must be met for the production of each phoneme, and then it generates trajectories of the articulatory movements that satisfy the constraints. Finally, the time sequence of spectra is estimated from the produced articulatory trajectories. The articulatory constraint of each phoneme does not change with the phonemic context, but the contextual variability of speech is reproduced because of the dynamic articulatory model. The accuracy of the synthesis model was evaluated using data collected by the simultaneous measurement of speech and articulatory movements. The accuracy of the phonemic timing estimates were measured and compared the synthesized results to the measured results. Experimental results showed that the model captured the contextual variability of both the articulatory movements and speech acoustics.     

共振峰编辑法区别鼻化元音中口、鼻音共振峰的实证探究*

为解决司法话者识别中利用鼻化元音构建元音声学空间图时如何准确判别鼻化元音的口、鼻音共振峰的问题。本文通过计算机语音工作站对语音样本的共振峰进行编辑操作，利用生成的语音样本构建不同的对照组分别进行听辨。结果表明，口音、鼻音共振峰分别被衰减后的语音变化特点呈现一定规律，使用此方法可以准确区分鼻化元音的口、鼻共振峰的阶次。本文建立的“共振峰编辑”与“听觉感知”相结合的判别方法，可以为司法话者识别及语音感知、识别等相关领域通过构建元音声学空间图进行声学特征研究的模型提供口音、鼻音共振峰的判别依据。     

Estimating the control parameters of an articulatory model from electromagnetic articulograph data

Finding the control parameters of an articulatory model that result in given acoustics is an important problem in speech research. However, one should also be able to derive the same parameters from measured articulatory data. In this paper, a method to estimate the control parameters of the the model by Maeda from electromagnetic articulography (EMA) data, which allows the derivation of full sagittal vocal tract slices from sparse flesh-point information, is presented. First, the articulatory grid system involved in the model's definition is adapted to the speaker involved in the experiment, and EMA data are registered to it automatically. Then, articulatory variables that correspond to measurements defined by Maeda on the grid are extracted. An initial solution for the articulatory control parameters is found by a least-squares method, under constraints ensuring vocal tract shape naturalness. Dynamic smoothness of the parameter trajectories is then imposed by a variational regularization method. Generated vocal tract slices for vowels are compared with slices appearing in magnetic resonance images of the same speaker or found in the literature. Formants synthesized on the basis of these generated slices are adequately close to those tracked in real speech recorded concurrently with EMA.     

An articulatory basis for the labial-to-coronal effect: /pata/ seems a more stable articulatory pattern than /tapa/

This paper investigates the coordination between the jaw, the tongue tip, and the lower lip during repetition with rate increase of labial-to-coronal (L(a)C(o)) consonant-vowel-consonant-vowel disyllables (e.g., /pata/) and coronal-to-labial (C(o)L(a)) ones (e.g., /tapa/) by French speakers. For the two types of disyllables: (1) the speeding process induces a shift from two jaw cycles per disyllable to a single cycle; (2) this shift modifies the coordination between the jaw and the constrictors, and (3) comes with a progression toward either a L(a)C(o) attractor [e.g., (/pata/ or /tapa/) --> /patá/ --> /ptá/] or a C(o)L(a) one (e.g., /pata/ or /tapa/ --> /tapá/ --> /tpá/). Yet, (4) the L(a)C(o) attractor is clearly favored regardless of the initial sequencing. These results are interpreted as evidence that a L(a)C(o) CVCV disyllable could be a more stable coordinative pattern for the lip-tongue-jaw motor system than a C(o)L(a) one. They are discussed in relation with the so-called LC effect that is the preference for L(a)C(o) associations rather than C(o)L(a) ones in CV.CV disyllables in both world languages and infants' first words.     

On the sufficiency of compound target specification of isolated vowels and vowels in /bVb/ syllables.

It has been suggested [e.g., Strange et al., J. Acoust. Soc. Am. 74, 695-705 (1983); Verbrugge and Rakerd, Language Speech 29, 39-57 (1986)] that the temporal margins of vowels in consonantal contexts, consisting mainly of the rapid CV and VC transitions of CVC's, contain dynamic cues to vowel identity that are not available in isolated vowels and that may be perceptually superior in some circumstances to cues which are inherent to the vowels proper. However, this study shows that vowel-inherent formant targets and cues to vowel-inherent spectral change (measured from nucleus to offglide sections of the vowel itself) persist in the margins of /bVb/ syllables, confirming a hypothesis of Nearey and Assmann [J. Acoust. Soc. Am. 80, 1297-1308 (1986)]. Experiments were conducted to test whether listeners might be using such vowel-inherent, rather than coarticulatory information to identify the vowels. In the first experiment, perceptual tests using "hybrid silent center" syllables (i.e., syllables which contain only brief initial and final portions of the original syllable, and in which speaker identity changes from the initial to the final portion) show that listeners' error rates and confusion matrices for vowels in /bVb/ syllables are very similar to those for isolated vowels. These results suggest that listeners are using essentially the same type of information in essentially the same way to identify both kinds of stimuli. Statistical pattern recognition models confirm the relative robustness of nucleus and vocalic offglide cues and can predict reasonably well listeners' error patterns in all experimental conditions, though performance for /bVb/ syllables is somewhat worse than for isolated vowels. The second experiment involves the use of simplified synthetic stimuli, lacking consonantal transitions, which are shown to provide information that is nearly equivalent phonetically to that of the natural silent center /bVb/ syllables (from which the target measurements were extracted). Although no conclusions are drawn about other contexts, for speakers of Western Canadian English coarticulatory cues appear to play at best a minor role in the perception of vowels in /bVb/ context, while vowel-inherent factors dominate listeners' perception.