Domain-initial strengthening refers to variation in the phonetic properties of consonants and vowels when occurring after a prosodic boundary and according to the strength of this boundary (the stronger the boundary, the stronger the strengthening). This strengthening results in a spatial expansion of articulatory movements and the enhancement of (some of) the segment’s contrastive acoustic properties (see , ). Concomitant changes in timing have also been reported for strengthened segments. Although lengthening of domain-initial segments has not been found to be systematic, especially in French [2, 3], overlap between consonants in #CC clusters (with “#” representing a prosodic boundary) tends to decrease with increased boundary strength [4, 5]. A recent study on French V-to-V coarticulation in #V1CV2 sequences also showed a reduced anticipatory coarticulation of V2 on V1 when it is initial in a strong prosodic domain . In the present study we test for a change in C-to-V coarticulation in French according to the prosodic position of the sequence (IP initial vs. word medial) and we look at different types of coarticulation varying in terms of cohesiveness by comparing : carryover coarticulation in CV sequences (where the overlap between segments is rather stable) and anticipatory coarticulation VC sequences (more variable and possibly more affected by other factors, as prosodic position).
About 17,000 vowels extracted from two large corpora (ESTER  and NCCFr ) of natural speech are studied. These includes /i, e, a, ɔ/ in uvular /R/ vs. coronal /t, d, s, z, n, l/ contexts in VC sequences. CV sequences in the same uvular vs. coronal contexts could also been observed for /a/ (but not for the other vowels due to insufficient number of cases). C-to-V coarticulation is compared between sequences that are either initial in an Intonational Phrase (IPi) or medial in a word (Wm). In Wm position, the opposite context (left in VC and right in CV) is a labial consonant. While in the CV sequence, C and V are always tautosyllabic, we could not control for the syllabic affiliation of C in the VC cases. Coarticulation is measured as the difference in F1 and F2 according to consonantal context. Analysis is performed using a linear mixed model in R  and the package lme4 .
Results show a clear effect of consonantal context in both VC and CV structures : as expected, F1 is significantly lower and F2 higher in coronal context than in uvular context. Prosodic position affects both F1 and F2 dimensions in a vowel-dependent way. When in IPi position, /a/ has a higher F1 (and F2 in VC only), /e/ has a lower F1 and a higher F2, /i/ has a higher F2, while no change is found for /ɔ/. More interestingly, our study reveals an interaction between the prosodic position and consonantal context. For all vowels in VC sequences, and for both F1 and F2, the effect of consonantal context is smaller in IPi position than in Wm position. This illustrated in Figure 1 for /aC/ and /eC/. In CV, the effect of consonantal context also interacts with prosodic position, although difference between prosodic positions is subtler.
This study based on a large amount of data produced in a naturalistic context shows that vowels in strong prosodic positions are less coarticulated, i.e. less overlapped by surrounding consonants, in French. These results will be discussed according to the proposed domain of activation of a π-gesture responsible of the slowing down of articulatory gestures near phrase boundaries. Overall, this reduced overlap undergone by prosodic domain initial vowels, and vowels in domain initial syllables, provides further support to the view that initial strengthening contributes to the preservation of segmental identity.
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