Realization and perception of French /R/ – REPER

The use of Electro-Magnetic Articulograph allowed – with the use of coils attached to the tongue and at the lower extremity of the velum – to determine the position of articulators with a good spatial and temporal precision. This in turn allows to analyze the realization of /R/ within the greatest number of contexts.
As for the velum that would lower so as to facilitate the contact with the back of the tongue, that question could only be answered through this experimental protocol. However, it had to be coupled with aerodynamic measurements in order to observe a possible nasal airflow. Indeed the lowering of the velum is not necessarily coupled with flows going through the nasal cavity. Finally, an analysis of subglottal pressure and of the different pressures up to the higher extremity of the vocal tract enables to understand all sorts of variations and possible compensation phenomena, for similar articulatory positions. Acoustic measurements on large corpora (50 hours of speech).

We have shown that the degree of constriction between the tongue and the palate is correlated to voicing and validate the use of Harmonic to Noise Ratio (HNR) as a tool for the acoustic measurement of the variability of /R/. Aerodynamic analyses showed that the increase of nasal airflow during the production of /R/ is not significant despite the opening of the velum as observed by Electro-Magnetic Articulograph. Subglottal pressure only varies for specific productions, at the end of sentences or under emphasis.
Finally, acoustic analyses of large corpora (over 50 hours of speech) displayed the influence of new predictors in the variation of /R/ such as lexical frequency, intonational contour, the position of the phoneme inside the prosodic group and speech rate. While these predictors are not new per se and apply to the other phoneme, their influence is greater on /R/ due to the Aerodynamic Voicing Constraint : the fact that /R/ is much backwards in the vocal tract emphasizes its voicing/unvoicing and its relation to stricture.

Two PhD theses are still in progress in the laboratory of the principal investigator, the first one in relation with automatic alignment of automatic speech recognition tools, and the second that draws a parallel with /R/ in Moroccan Berber which phonologically has both voiced and unvoiced realizations, this in turn will allow to determine whether the limits in variation observed for French can also be found.
A new research project will start in 2018 in the laboratory on the variations specific to each speaker and the analysis of /R/ known as a diaphasic index will go in this light of research.

Beyond the publications detailed in the form, this project allowed –thanks to the acoustic measurements in comparison with the physiological data – to program a didactic software that anyone can use to practice its /R/ realization with the use of a microphone, and freely downloadable here : www.univ-paris3.fr/anr-reper-231657.kjsp
This tool, together with the use of an ultrasound were showed for the last two editions of the “fête de la science” for the teaching of /R/ pronunciation.

Standard French /R/ is - like most rhotics - characterized by a great deal of variability. According to the literature, its differents realizations are mainly due to proprieties of contiguous phonemes and to its position in the word. These accounts leave unexplained a great deal of realizations labeled as "free variants". Phonetically, it could be realized most frequently as a fricative, a trill, an approximant, voiced, unvoiced or sometimes partially unvoiced.

These troubles in understanding variations of French /R/ imply a number of consequences : learners of French have great difficulties with the acquisition of this sound, Automatic Speech Recognition systems - even though they manage to modelize this sound as a function of its contiguous sounds - use pronunciation dictionaries that are overly simplified for words containing /R/. As for phonological theories, they usually consider it as specific because of, among other reasons, its propensity to fluctuate between obstruents and sonorants.

In the project REPER, we hypothesize that articulatory variation is structured according to a continuum going from voiced approximant to voiceless fricative. Realizations outside this continuum can be explained by a series of prosodic and semantic factors mostly. These different realizations and great sensibility to reduction compared to other phonemes suggests a possible on-going evolution of French /R/. An acoustic target (rather than articulatory) seems to be the most important point of stability across these realizations. This acoustic target is found in formant trajectories of contiguous vowels : a rise in first and third formants.

We will investigate the status of French /R/ in three working packages that complete each other and allow a complete comprehension of the phenomenon :

- A first working package dealing with acoustic analyses of large corpora of approximately a hunded hours of continuous speech (also comparing two styles: journalistic and spontaneous speech, and comparing journalistic french to a corpus of journalistic german in order to evaluate the variation of /R/ in both languages as these two phonemes have some similtudes). All corpora are already available and have been tagged for analysis by the coordinator. Large corpora of continuous speech - and them alone - allow to quantify the different realizations of /R/, the amplitude of its variation along with the number of strategies and their usage. They will also enable to clarify the sources of variations only available in large continuous speech studies such as the grammatical, semantic, pragmatic, syntacic and phonotactic context of /R/.

- The second working package is a multi-sensor physiological analysis (using a controlled corpus) so as to analyze the articulatory gestures of friction (through ultrasound device and piezoelectric accelerometer) and voicing (through the non invasive External PhottoGlottoGraph recently patented by the Laboratory of Phonetics and Phonology) whether they go along that hypothesized continuum going from voiced approximant to voiceless fricative. A comparison between the acoustic target of F1 and F3 raising and the articulatory variability will be discussed
This device ready to use in our laboratory will help determine the intended articulatory gestures and their timing in an articulatory phonology framework. Compared to French liquid /l/, the fricative /Z/ and the plosive /g/, we will compared their voicing and devoicing pattern, as well their approximant realization in specific contexts.

- The third working package deals with perception and will explore the representation of the French /R/ in the brain. Firstly, we will test on French naive listeners the identification of graphical /R/ despite its numerous realization variants. In a second step, we will try and show their ability to discriminate between allophones of /R/ with classical behavioural perception tests and with an Electro-Encephalo-Graphic experiment.