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Articulatory token-to-token variability not only depends on linguistic aspects like the phoneme inventory of a given language but also on speaker specific morphological and motor constraints. As has been noted previously (Perkell (1997), Mooshammer et al. (2004)), speakers with coronally high "domeshaped" palates exhibit more articulatory variability than speakers with coronally low "flat" palates. One explanation for that is based on perception oriented control by the speaker. The influence of articulatory variation on the cross sectional area and consequently on the acoustics should be greater for flat palates than for domeshaped ones. This should force speakers with flat palates to place their tongue very precisely whereas speakers with domeshaped palates might tolerate a greater variability. A second explanation could be a greater amount of lateral linguo-palatal contact for flat palates holding the tongue in position. In this study both hypotheses were tested.
In order to investigate the influence of the palate shape on the variability of the acoustic output a modelling study was carried out. Parallely, an EPG experiment was conducted in order to investigate the relationship between palate shape, articulatory variability and linguo-palatal contact.
Results from the modelling study suggest that the acoustic variability resulting from a certain amount of articulatory variability is higher for flat palates than for domeshaped ones. Results from the EPG experiment with 20 speakers show that (1.) speakers with a flat palate exhibit a very low articulatory variability whereas speakers with a domeshaped palate vary, (2.) there is less articulatory variability if there is lots of linguo-palatal contact and (3.) there is no relationship between the amount of lateral linguo-palatal contact and palate shape. The results suggest that there is a relationship between token-to-token variability and palate shape, however, it is not that the two parameters correlate, but that speakers with a flat palate always have a low variability because of constraints of the variability range of the acoustic output whereas speakers with a domeshaped palate may choose the degree of variability. Since linguo-palatal contact and variability correlate it is assumed that linguo-palatal contact is a means for reducing the articulatory variability.
Articulatory token-to-token variability not only depends on linguistic aspects like the phoneme inventory of a given language but also on speaker specific morphological and motor constraints. As has been noted previously (Perkell (1997), Mooshammer et al. (2004)) , speakers with coronally high "domeshaped" palates exhibit more articulatory variability than speakers with coronally low "flat" palates. One explanation for that is based on perception oriented control by the speaker. The influence of articulatory variation on the cross sectional area and consequently on the acoustics should be greater for flat palates than for domeshaped ones. This should force speakers with flat palates to place their tongue very precisely whereas speakers with domeshaped palates might tolerate a greater variability. A second explanation could be a greater amount of lateral linguo-palatal contact for flat palates holding the tongue in position. In this study both hypotheses were tested.
Mechanisms of contrasting korean velar stops : A catalogue of acoustic and articulatory parameters
(2003)
The Korean stop system exhibits a three-way distinction in velar stops among /g/, /k'/ and /kh/. If the differentiation is regarded as being based on voicing, such a system is rather unusual because even a two-way distinction between a voiced and a voicless unaspirated velar stop gets easily lost in the languages of the world especially in the case of velar stops. One possibility for maintainig this distinction is that supralaryngeal characteristics like articulators' velocity, duration of surrounding vowels or stop closure duration are involved. The aim of the present study is to set up a catalogue of parameters which are involved in the distinction of Korean velar stops in intervocalic position.
Two Korean speakers have been recorded via Electromagnetic Articulography. The word material consisted of VCV-sequences where V is one of the three vowels /a/, /i/ or /u/ and C one of the Korean velars /g/, /k'/ or /kh/. Articulatory and acoustic signals have been analysed It turned out that the distinction is only partly built on laryngeal parameters and that supralaryngeal characteristics differ for the three stops. Another result is that the voicing contrast is not a matter of one parameter, but there is always a set of parameters involved. Furthermore, speakers seem to have a certain freedom in the choice of these parameters.
Temporal development of compensation strategies for perturbed palate shape in German /S/-production
(2006)
The palate shape of four speakers was changed by a prosthesis which either lowered the palate or retracted the alveoles. Subjects wore the prosthesis for two weeks and were recorded several times via EMA. Results of articulatory measurements show that speakers use different compensation methods at different stages of the adaptation. They lower the tongue immediately after the insertion of the prosthesis. Other compensation methods as for example lip protrusion are only acquired after longer practising periods. The results are interpreted as supporting the existence of different mappings between motor commands, vocal tract shape and auditory-acoustic target.
As has been noted previously, speakers with coronally low "flat" palates exhibit less articulatory variability than speakers with coronally high "domeshaped" palates. This phenomenon is investigated by means of a tongue model and an EPG experiment. The results show that acoustic variability depends on the shape of the vocal tract. The same articulatory variability leads to more acoustic variability if the palate is flat than if it is domeshaped. Furthermore, speakers with domeshaped palates show more articulatory variability than speakers with flat palates. The results are explained by different control strategies by the speakers. Speakers with flat palates reduce their articulatory variability in order to keep their acoustic variability low.
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.
Proper speech production requires auditory speech feedback control. Models of speech production associate this function with the right cerebral hemisphere while the left hemisphere is proposed to host speech motor programs. However, previous studies have investigated only spectral perturbations of the auditory speech feedback. Since auditory perception is known to be lateralized, with right-lateralized analysis of spectral features and left-lateralized processing of temporal features, it is unclear whether the observed right-lateralization of auditory speech feedback processing reflects a preference for speech feedback control or for spectral processing in general. Here we use a behavioral speech adaptation experiment with dichotically presented altered auditory feedback and an analogous fMRI experiment with binaurally presented altered feedback to confirm a right hemisphere preference for spectral feedback control and to reveal a left hemisphere preference for temporal feedback control during speaking. These results indicate that auditory feedback control involves both hemispheres with differential contributions along the spectro-temporal axis.
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'.
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.
This paper shows that several typologically unrelated languages share the tendency to avoid voiced sibilant affricates. This tendency is explained by appealing to the phonetic properties of the sounds, and in particular to their aerodynamic characteristics. On the basis of experimental evidence it is shown that conflicting air pressure requirements for maintaining voicing and frication are responsible for the avoidance of voiced affricates. In particular, the air pressure released from the stop phase of the affricate is too high to maintain voicing, which in consequence leads to a devoicing of the frication part.