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Low- dimensional and speaker-independent linear vocal tract parametrizations can be obtained using the 3-mode PARAFAC factor analysis procedure first introduced by Harshman et al. (1977) and discussed in a series of subsequent papers in the Journal of the Acoustical Society of America (Jackson (1988), Nix et al. (1996), Hoole (1999), Zheng et al. (2003)). Nevertheless, some questions of importance have been left unanswered, e.g. none of the papers using this method has provided a consistent interpretation of the terms usually referred to as "speaker weights". This study attempts an exploration of what influences their reliability as a first step towards their consistent interpretation. With this in mind, we undertook a systematic comparison of the classical PARAFAC1 algorithm with a relaxed version, of it, PARAFAC2. This comparison was carried out on two different corpora acquired by the articulograph, which varied in vowel qualities, consonantal contexts, and the paralinguistic features accent and speech rate. The difference between these statistical approaches can grossly be described as follows: In PARAFAC1, observation units pertain to the same set of variables and the observation units are comparable. In PARAFAC2, observations pertain to the same set of variables, but observation units are not comparable. Such a situation can be easily conceived in a situation such as we are describing: The operationalization we took relies on the comparability of fleshpoint data acquired from different speakers, which need not be a good assumption due to influences like sensor placement and morphological conditions.
In particular, the comparison between the two different approaches is carried out by means of so-called "leverages" on different component matrices originating in regression analysis, calculated as v = diag(A(A A)−1A ) and delivering information on how "influential" a particular loading matrix is for the model. This analysis could potentially be carried out component by component, but we confined ourselves to effects on the global factor structure. For vowels, the most influential loadings are those for the tense cognates of non-palatal vowels. For speakers, the most prominent result is the relative absence of effects of the paralinguistic variables. Results generally indicate that there is quite little influence of the model specification (i.e. PARAFAC1 or PARAFAC2) on vowel and subject components. The patterns for the articulators indicate that there are strong differences between speakers with respect to the most influential measurement as revealed by PARAFAC2: In particular, the most influential y-contribution is the tongue-back for some talkers and the tongue-dorsum for other speakers. With respect to the speaker weights, again, the leverage patterns are very similar for both PARAFAC-versions. These patterns converge with the results of the loading plots, where the articulator profiles seem to be most altered by the use of PARAFAC2. These findings, in general, are interpreted as evidence for the reliability of the PARAFAC1 speaker weights.
This work investigates laryngeal and supralaryngeal correlates of the voicing contrast in alveolar obstruent production in German. It further studies laryngealoral co-ordination observed for such productions. Three different positions of the obstruents are taken into account: the stressed, syllable initial position, the post-stressed intervocalic position, and the post-stressed word final position. For the latter the phonological rule of final devoicing applies in German. The different positions are chosen in order to study the following hypotheses:
1. The presence/absence of glottal opening is not a consistent correlate of the voicing contrast in German.
2. Supralaryngeal correlates are also involved in the contrast.
3. Supralaryngeal correlates can compensate for the lack of distinction in laryngeal adjustment.
Including the word final position is motivated by the question whether neutralization in word final position would be complete or whether some articulatory residue of the contrast can be found.
Two experiments are carried out. The first experiment investigates glottal abduction in co-ordination with tongue-palate contact patterns by means of simultaneous recordings of transillumination, fiberoptic films and Electropalatography (EPG). The second experiment focuses on supralaryngeal correlates of alveolar stops studied by means of Electromagnetic Articulography (EMA) simultaneously with EPG. Three German native speakers participated in both recordings. Results of this study provide evidence that the first hypothesis holds true for alveolar stops when different positions are taken into account. In fricative production it is also confirmed since voiceless and voiced fricatives are most of the time realised with glottal abduction. Additionally, supralaryngeal correlates are involved in the voicing contrast under two perspectives. First, laryngeal and supralaryngeal movements are well synchronised in voiceless obstruent production, particularly in the stressed position. Second, supralaryngeal correlates occur especially in the post-stressed intervocalic position. Results are discussed with respect to the phonetics-phonology interface, to the role of timing and its possible control, to the interarticulatory co-ordination, and to stress as 'localised hyperarticulation'.
Rate effects on aerodynamics of intervocalic stops : evidence from real speech data and model data
(2008)
This paper is a first attempt towards a better understanding of the aerodynamic properties during speech production and their potential control. In recent years, studies on intraoral pressure in speech have been rather rare, and more studies concern the air flow development. However, the intraoral pressure is a crucial factor for analysing the production of various sounds.
In this paper, we focus on the intraoral pressure development during the production of intervocalic stops.
Two experimental methodologies are presented and confronted with each other: real speech data recorded for four German native speakers, and model data, obtained by a mechanical replica which allows reproducing the main physical mechanisms occurring during phonation. The two methods are presented and applied to a study on the influence of speech rate on aerodynamic properties.
In this paper the issue of the nature of the representations of the speech production task in the speaker's brain is addressed in a production-perception interaction framework. Since speech is produced to be perceived, it is hypothesized that its production is associated for the speaker with the generation of specific physical characteristics that are for the listeners the objects of speech perception. Hence, in the first part of the paper, four reference theories of speech perception are presented, in order to guide and to constrain the search for possible correlates of the speech production task in the physical space: the Acoustic Invariance Theory, the Adaptive Variability Theory, the Motor Theory and the Direct-Realist Theory. Possible interpretations of these theories in terms of representations of the speech production task are proposed and analyzed. In a second part, a few selected experimental studies are presented, which shed some light on this issue. In the conclusion, on the basis of the joint analysis of theoretical and experimental aspects presented in the paper, it is proposed that representations of the speech production task are multimodal, and that a hierarchy exists among the different modalities, the acoustic modality having the highest level of priority. It is also suggested that these representations are not associated with invariant characteristics, but with regions of the acoustic, orosensory and motor control spaces.
Studying kinematic behavior in speech production is an indispensable and fruitful methodology in order to describe for instance phonemic contrasts, allophonic variations, prosodic effects in articulatory movements. More intriguingly, it is also interpreted with respect to its underlying control mechanisms. Several interpretations have been borrowed from motor control studies of arm, eye, and limb movements. They do either explain kinematics with respect to a fine tuned control by the Central Nervous System (CNS) or they take into account a combination of influences arising from motor control strategies at the CNS level and from the complex physical properties of the peripheral speech apparatus. We assume that the latter is more realistic and ecological. The aims of this article are: first, to show, via a literature review related to the so called '1/3 power law' in human arm motor control, that this debate is of first importance in human motor control research in general. Second, to study a number of speech specific examples offering a fruitful framework to address this issue. However, it is also suggested that speech motor control differs from general motor control principles in the sense that it uses specific physical properties such as vocal tract limitations, aerodynamics and biomechanics in order to produce the relevant sounds. Third, experimental and modelling results are described supporting the idea that the three properties are crucial in shaping speech kinematics for selected speech phenomena. Hence, caution should be taken when interpreting kinematic results based on experimental data alone.
The present article illustrates that the specific articulatory and aerodynamic requirements for voiced but not voiceless alveolar or dental stops can cause tongue tip retraction and tongue mid lowering and thus retroflexion of front coronals. This retroflexion is shown to have occurred diachronically in the three typologically unrelated languages Dhao (Malayo-Polynesian), Thulung (Sino-Tibetan), and Afar (East-Cushitic). In addition to the diachronic cases, we provide synchronic data for retroflexion from an articulatory study with four speakers of German, a language usually described as having alveolar stops. With these combined data we supply evidence that voiced retroflex stops (as the only retroflex segments in a language) did not necessarily emerge from implosives, as argued by Haudricourt (1950), Greenberg (1970), Bhat (1973), and Ohala (1983). Instead, we propose that the voiced front coronal plosive /d/ is generally articulated in a way that favours retroflexion, that is, with a smaller and more retracted place of articulation and a lower tongue and jaw position than /t/.
The present paper offers a summary of the results of two earlier experiments (Nawrocki and Gonet 2004; Nawrocki 2004), in which acoustic properties of the voiceless velar fricative phoneme /x/ in Southern Polish were investigated.
As is found in both studies (Nawrocki and Gonet 2004; Nawrocki 2004), speakers of both genders favour glottal articulation, with partial or full voicing. Word final contexts are decisively in favour of [x]. The word initial, prevocalic positions seem to allow quite a number of allophonic variants of /x/ . These are: [x], [ɦ], [ç] and, additionally, the voiceless glottal, the pharyngeal or the epiglottal [h]/[ħ]/[ʜ]. Another factor taken into account is the coarticulation effect of the vocalic context on the choice of articulation. Based on the results of the experiments, a reformulated allophonic composition is proposed for Polish /x/. It makes room for previously unconsidered pharyngeal and glottal allophones.
In order to inspect the acoustic properties of the allophones of Polish /x/ further, their static and dynamic spectral features are compared to those of phonetically similar sounds in other languages where they have the status of independent phonemes. Special attention is paid to the distribution of spectral peaks and their intensity. The fact that in Polish there are no 'back' fricative phonemes that would contrast with /x/ creates a wide range of acceptable allophonic articulations that cannot be challenged from either articulatory or perceptual points of view.
This paper describes the processing of MRI and CT images needed for developing a 3D linear articulatory model of velum. The 3D surface that defines each organ constitutive of the vocal and nasal tracts is extracted from MRI and CT images recorded on a subject uttering a corpus of artificially sustained French vowels and consonants. First, the 2D contours of the organs have been manually extracted from the corresponding images, expanded into 3D contours, and aligned in a common 3D coordinate system. Then, for each organ, a generic mesh has been chosen and fitted by elastic deformation to each of the 46 3D shapes of the corpus. This has finally resulted in a set of organ surfaces sampled with the same number of 3D vertices for each articulation, which is appropriate for Principal Component Analysis or linear decomposition. The analysis of these data has uncovered two main uncorrelated articulatory degrees of freedom for the velum's movement. The associated parameters are used to control the model. We have in particular investigated the question of a possible correlation between jaw / tongue and velum's movement and have not find more correlation than the one found in the corpus.
A visual articulatory model and its application to therapy
of speech disorders : a pilot study
(2005)
A visual articulatory model based on static MRI-data of isolated sounds and its application in therapy of speech disorders is described. The model is capable of generating video sequences of articulatory movements or still images of articulatory target positions within the midsagittal plane. On the basis of this model (1) a visual stimulation technique for the therapy of patients suffering from speech disorders and (2) a rating test for visual recognition of speech movements was developed. Results indicate that patients produce recognition rates above level of chance already without any training and that patients are capable of increasing their recognition rate over the time course of therapy significantly.