[Geometrical growth models of the fetal forebrain, cerebellum, brainstem and change of the cranial base angles during fetal period]. / Modèles géométriques de croissance du cerveau, cervelet, tronc cérébral et modification des angles de la base du crâne au cours de la période fœtale.

INTRODUCTION: Brain growth plays likely an important role for the skull growth. In the fetus, there exists an heterochrony for the growth of supratentorial (forebrain) and infratentorial regions (brainstem and cerebellum). The aim of the study was thus to model geometrically the growth of these two regions and to compare it with the inflection of the base of skull. MATERIAL AND METHODS: Brain growth measurements were performed from midsagittal photographs of fetal brains obtained from an Anatomical Atlas over a period from 10 to 40 amenorrhea weeks (AW). After countouring and pointing anatomical and geometrical landmarks, we have developed a linear growth model based on principal component analysis (PCA). Besides, the variation of the sphenoidal and clivo-foraminal angles was studied from anatomical midsagittal slices of fetal heads sampled over a period from 16 to 39 AW. RESULTS: The PCA model brings to light the radial expansion of the forebrain growth (first component) associated with an inferior and posterior rotation of the occipital lobe. The growth of the infratentoriel region presents an inferior and posterior expansion associated with a second component corresponding to inferior and anterior expansions. From the 17 AW, appears an heterochrony between the supra- and infratentorial growths and an inversion of the ratio between the infra- and supratentorial dimensions after 30 AW. The sphenoidal and clivo-foraminal angles decrease slightly until 25 AW, and then increase quickly until the 39 AW. CONCLUSIONS: The growth of brain is accompanied by morphological change between the compartments supra- and infratentoriel but also on the level of the base of skull. The possible interactions will be discussed.

Detecting anticipatory events in handwriting movements.

We investigated how visual processes exploit specific anticipatory movements observed in handwriting gestures. Previous research has shown that the kinematic information contained in the downstroke of an l is exploited to predict the identity of the forthcoming letter. Here, we determined the moment at which prediction takes place. Two between-letter effects were examined: changes in size (ll vs le) and changes in rotation direction (le vs ln). Results show that with only 75% of the l downstroke trajectory (or 60% of the downstroke time) subjects are already capable of predicting the identity of the letter following the l, that is well before the end of the downstroke. Analysis also reveals that identification takes place after the presentation of the movement acceleration phase. The visual perception of motor anticipation seems to involve the detection of motor events.

Visual perception of motor anticipation in cursive handwriting: influence of spatial and movement information on the prediction of forthcoming letters.

The execution of a graphemic sequence is constrained by spatial demands that result in fluctuations of letter shape and movement time. When producing two letters (ll, le, or ln) the movement time and the letter shape of the first letter depend on the execution constraints of the second one. The motor system thus anticipates the production of the forthcoming graphemic sequence during the production of the first letter. An experiment is reported the aim of which was to examine whether the visual system could exploit this anticipatory information to predict the identity of the letter following the l. Different ls belonging to ll, le, and ln were presented on a screen. Subjects had to predict to which couple of letters (ll, le, or ln) the presented l belonged to, by using information on the shape of the l and/or the movement that produced it. Results showed that the percentages of correct responses were higher in the conditions where the stimulus provided kinematic information than in the condition in which only spatial information was available. The ability to predict the forthcoming letter seems to be mediated by implicit knowledge on motor anticipation rules.

Acoustic and perceptual effects of changes in vocal tract constrictions for vowels.

The purpose of this study was to use vocal tract simulation and synthesis as means to determine the acoustic and perceptual effects of changing both the cross-sectional area and location of vocal tract constrictions for six different vowels: Area functions at and near vocal tract constrictions are considered critical to the acoustic output and are also the central point of hypotheses concerning speech targets. Area functions for the six vowels, [symbol: see text] were perturbed by changing the cross-sectional area of the constriction (Ac) and the location of the constriction (Xc). Perturbations for Ac were performed for different values of Xc, producing several series of acoustic continua for the different vowels. Acoustic simulations for the different area functions were made using a frequency domain model of the vocal tract. Each simulated vowel was then synthesized as a 1-s duration steady-state segment. The phoneme boundaries of the perturbed synthesized vowels were determined by formal perception tests. Results of the perturbation analyses showed that formants for each of the vowels were more sensitive to changes in constriction cross-sectional area than changes in constriction location. Vowel perception, however, was highly resistant to both types of changes. Results are discussed in terms of articulatory precision and constriction-related speech production strategies.

Vocal tract area function estimation from midsagittal dimensions with CT scans and a vocal tract cast: modeling the transition with two sets of coefficients.

The generation of area functions from measurements of the sagittal section is an important step in the study of the relation between vocal tract geometry and speech acoustics. We present a new model to perform this transformation, inspired by the alpha beta model of Heinz & Stevens (1965). Our model is based on analysis of a vocal tract cast for large sagittal dimensions and for small sagittal dimensions on CT scans of the vocal tract constriction zones for the three cardinal vowels [i, a, u] of French. We extracted two sets of coefficients, appropriate for large and small sagittal dimensions respectively. We then compared the predictions of the model with those of other models from the literature. Finally, the usefulness of this dual coefficient procedure for the acoustic simulation of vowels was tested using sagittal sections generated by an acoustic model of the vocal tract.

[Influences of acoustic coupling between source and vocal tract of the Fo of oral vowels. Consequence for the study of intrinsic characteristics]. / Etude de l'influence du couplage acoustique source-conduit vocal sur Fo des voyelles orales. Conséquence pour l'étude des caractéristiques intrinsèques.

With the aid of a two-mass model of the vocal source loaded by the input impedance of the vocal tract, we first study theoretically, then by simulation, the effects of source-vocal tract coupling on the intrinsic frequencies Fo of the French oral vowels. We explain the correlation which exists between Fo and the frequency of the first formant as well as the results from the experiment described by Ishizaka and Flanagan [1972]. In conclusion, we show that the acoustic coupling cannot explain the different values of Fo, intrinsic in the vowels, but on the contrary, a physiological coupling has to compensate for the effects of acoustic coupling to explain the characteristics revealed in natural speech.

[Statistical study of laryngeal frequency. Application to the analysis and synthesis of prosodic features of French]. / Etude statistique de la fréquence laryngienne. Application à l'analyse et à la synthèse des faits prosodiques du français

Some precisions concerning the specification and the instruments developed for the measurement of laryngeal frequency F1 being stated, the authors give statistical results for French. In first approximation, the F1 distribution is gaussian for a given corpus; the standard deviation measured and given in percentage referring to the mean laryngeal frequency F1 is about 16% for male and female speakers. Ceteris partibus, the variations of F1 are relatively low for a given speaker from one record to an other (about +/- 1/2 tone). The means of F1 are given for samples (gaussian) concerning adults (30 males and 30 female): respectively 118 and 207 Hz with standard deviation sigma (F1) of 18 and 20 Hz. The ratio tau 1 of the voiced duration to the total duration of the corpus, dependant on the sex: 0.50 for men and 0.63 for women (the difference is significant at the 0.001 level) allows the specification of the speaking rate. When the speaking rate increases, the length of pauses decreases. These results can be used for an estimation of the precision of the statistical measurement of F1 and sigma (F1), in relation to the number of periods N. To N appears a total duration of the corpus determined by tau 1. A comparison is made between the results of the calculation and the measurement. The F1 specification can be used for determination of the vocal source of synthesizer to improve naturalness of synthetic sounds and for analysis and synthesis of prosodic features using the results of two previous papers which have allowed to specify the position of level 1, 2 and 4 and to show the differences in the perceptual importance of the variations introduced in connection with the three levels.