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THE ROLE OF PROSODY IN THE SHAPING OF ARTICULATION IN ITALIAN CV SYLLABLES

Edda Farnetani and Mario Vayra

Centro di Fonetica de1 CNR, Padova Italy Scuo1a Normale Superiore, Pisa Italy

ABSTRACT This study explores (by means of EPG) the variations in the articulation of vowels and of consonant /t/ in CV syllab1es of trisyllabic words, as a function of 1exical stress, word/ sentence boundaries, and the context in which the word is produced (in isolation or embed­ded in a sentence). The goal is to assess the nature of these changes, and the degree to which they affect V and/or C. The results show that stress and boundaries affect the whole syllable: in stressed syllables and in those signalling prosodic boundaries the CV contrast is enhanced and the CV coarticulatory effects tend to decrease. How­ever, only the changes induced by stress re­sult in an enhancement of the vowe1-specific distinctive qualities.

RESUME Cette etude explore les vanatwns de 1' articulation des voyelles et de la consonne /t/ dans 1es syllabes CV de mots trisyllabiques, en fonction de 1' accent 1exical, des frontieres du mot et de la phrase, et du contexte dans lequel le mot est produit. L' objectif de cette etude est de determiner la nature de ces vari­ations, et le degre de changement de 1' articu1ation de la voyelle et de la consonne. Les donnees montrent que les effets de 1' accent et des frontieres s 'exercent sur la syllabe entiere: dans 1es syllabes accentuees et dans celles qui marquent les frontieres, le contraste entre C et V est renforce, et 1es effets de la coarticulation sont affaiblis. Toutefois, seulement 1' accent comporte un renforcement des qualites distinctives speci:fiques de chaque voyelle.

1. Introduction The goal of this study is to determine how lexical stress contrast, word/sentence bounda­ries, and utterance type are reflected in the articulation of CV syllables. It continues pre­vious work on vowel reduction, where the effects of word position within a sentence were investigated for vowe1 /a/ [1]. The present study centers on the syllable, with two main perspectives. The first is to know

whether the above mentioned factors affect V and C in a similar way, or eise, if it is C or V to better reflect the one or the other vari­ables. The second is to know whether the re­lation between C and V is modified under the different prosodic conditions. The fmal goal is to shed light on the contro1 mechanism underlying the observed effects. Variations in spatial configuration reflecting an increase/ decrease in movement displacement may be the automarle resu1t of temporal changes, but can also be brought about by other control strategies. According to the new version of the vowel undershoot model [2], movement displacements are accounted for by three vari­ables: duration, input force, and speed of the system response, which reflect different strat­egies avai1ab1e to speakers under different communicative conditions. The studies of the relation between prosody and articulation concem English, and are quite recent. As for the e:ffects of stress and accent, the study of de Jong [3] on ·English (C)VC syllables shows that, under nuclear accent (as

· compared to 1ower-level stress conditions) both vowels and consonants are produced with larger movement amplitudes, and most often with an increase in movement velocity. Such effects are interpreted as localized hy­perarticulation of both V and C, in alterna­tive to the sonority expansion model [4]. As for prosodic boundaries, the investigation by Edwards et al. [5] indicates that the articula­tion of finallengthening can be brought about by slowing down the articu1atory movements and/or by decreasing the temporal overlap between C and V. Preliminary results of an EPG study by Fougeron and Keating [ 6] on CV syllables in various phrasal positions in­dicate that boundaries are marked by a strengthening of voweVconsonant contrast. fu line with de Jong's hyperarticulation hypoth­esis for accented syllables, Keating [7] pro­poses that also initial boundaries are charac­terized by hyperarticulation. These studies indicate that the hyper/hypospeech model, devised by Lindbiom [8] for accounting for speech style differences, appears to work lo­cally for signalling a variety oflinguistic pro-

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sodic contrasts. 2. Method The corpus consists of nonsense CVCVCV trisyllables, where C= /t/ and V= Ja/, or /i/, or Iu/ in symmetric sequences; lexical stress var­ies across the three syllables. The words were produced in isolation (IS), in sentence near­initial position (U go ... della Torre partl per la Francia) (IN), andin sentence fmal position (Pani per la Francia col marchese Ugo ... ) (FN). The material was repeated 5 to 6 times by two Northem speakers of Standard Ital­ian. The artificial palate contains 62 electrodes divided in eight rows from front to back (Rl...R8) and four columns (in each half of the surface ). The articulation of consonant /t/ was analyzed with the following E.PG meas­ures: tongue tip/blade contact (FRCONT) (percent contact in the region defined by the five front rows), Tongue Body Contact (TBCONT) (the same for the three back rows). The measures for vowels were (TBCONT), tongue body Centrality Index (CI), and Posteriority Index (PI). CI is the nurober of on-electrodes in the columns in­tersecting the back row exhibiting maximuro central contact, and ranges from 0 to 8 as a function of the increase of on-electrodes from the side to the central columns; the nurober is corrected by subtracting a fixed value of 0.33 or 0.66, when one or two back rows, respec­tively, exhibit less central contact than the one with maximum contact PI corresponds to the row nurober where the frontmost contact oc­curs, and thus ranges from 1 to 8 (score 9 was assigned for complete absence of con­tact, which sometimes occurs for /a/). The asymmetries in the frontmost contact were accounted for by adding a fixed value of 0.5 to row nurober when the contact was on one side only. The measures were taken at the midpoint of maximum front contact for Cs, and, for V s, at the points of maxima or minima according to vowel type. The significance level for statistical analysis was set at p<O.O 1. The data on duration are not reported in this short version of the paper.

3. Results 3.1 Vowels. The data indicate that for vowels the most

powerful factor is Stress, followed by sylla­ble position within the word, followed by ut­terance type (which has significant effects only for GA). Stress. Table 1 shows the values of the three vowel parameters as a function of stress.

Tab~e 1. Effects of stress on vowels EF Ia/ s u R2

TBCONT 3.73 17.97 0. 729 CI 0.46 1. 68 0. 710 PI 8.57 6.64 0.542

/i/ TBCONT 53.10 49.95 0.073 CI 4.36 4.09 0.070 PI 2.54 1. 95 0.176

Iu/ TBCONT 24.29 26.02 0.019 ns CI 2.56 2.31 0.038 ns PI 6.68 5.46 0.217

GA Ia/

TBCONT 10.87 23.64 0.566 CI 1. 44 2.26 0.443 PI 7.74 6.53 0.425

/i/ TBCONT 59.84 55.97 0.095 CI 5.16 4.88 0.065 PI 4.08 2.78 0.217

Iu/ TBCONT 31.72 33.81 0.012 ns CI 4.01 3.62 0.067 PI 6.77 5.64 0.156

It can be seen that the trends are very consist­ent across the subjects. In stressed versus un­stressed syllables, forvowel Ja/ the global TB contact and the central contact decrease, while posteriority increases, suggesting a more open mouth configuration and (possibly) a more posterior constriction. For /i/, TB contact in­creases, as well as centrality; PI indicates that the frontmost tongue contact, which may ex­tend till the dento-alveolar region, reaches only the postalveolar region under stress. For one subject (EF) the TB configuration allowed us to measure also the location of maximuro constriction, which was found to be located at the center of the mediopalatal region (ROW 6-7) in stressed syllables, and more fronted (ROW 5-6) in unstressed syllables (p<0.001): thus stress induces in /i/ a more elevated tongue body, a tighter constriction and an in-

. creased posteriority. The data for Iu/ are less systematic: TBCONT and CI suggest that in stressed position there is an increase in posteriority and that the tongue body de­creases the global contact but increases the central contact. The increase in posteriority for a11 stressed vowels (that we hypothesize be brought about by a lowering of the jaw) indicates that they are less subject to the coarticulatory effects of the stop consonant than unstressed V s, while the other two pa-

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rameters indicate an increase of tongue body displacement towards the V specific targets. It clearly appears that stress enhances the vowel-specific distinctive properties at a high degree. For GA these qualities are further enhanced in isolated words. Interactions be­tween the variables indicate that unstressed V s in word medial syllables exhibit the maxi­mum degree of reduction, and that the para­digmatic contrast between stressed and un­stressed V s tends to weaken at word bounda­ries, and even more at utterance boundaries.

Boundaries. Comparisons between syllables at word boundaries and word-medial sylla­bles indicate that parameters TBCONT and PI, but not CI are consistent across conditions and subjects. Stressed vowels in initial sylla­bles, either sentence or word-initial, exhibit a significant increase in PI (+PI), but no sig­nificant changes in TBCONT (with the nota­ble exception of Ia/ in the first syllable of em­bedded words for EF, where the contact de­creases significantly). This indicates that glo­bally, in initial syllables, stressed vowels do not further enhance their distinctive proper­ties but just tend to be produced with a more open vocal tract in front of the constriction. Also sentence-final vowels tend to open: for {lf and /u/ there is -TBCONT associated with +PI, which suggests that in this position close vowels tend tobe produced not only with less front contact, but also with a less tight con­striction. Word final boundaries are never sig­nalled. The changes observed in unstressed vowels parallel those observed in stressed vowels, but are larger in amount and all highly sig­nificant: In sentence- and word-initial sylla­bles unstressed vowels are a1l produced with a more open front cavity (+PI) and for EF with decrease TBCONT. For GA, TB de­creases for Ia/ but tend to increase for close vowels indicating that unstressed Vs in ini­tial position are also less reduced. Sentence­fmal boundaries are always signalled by +PI and -TBCONT, following the general trend. No changes occur for word-final boundaries. The overall data indicate that the increase in PI at both initial and final boundaries, which is much stronger and systematic in unstressed than in stressed V s, may account, better that TBCONT, for the decrease in Stressfunstress contrast at the edges of words and sentences.

3.2. Gonsonant/tl For the consonant, the strongest effects are exerted by factor utterance type, followed by

syllable position and stress: for both subjects FRCONT is greater when the word is spo­

. keii in isolation, in word initial syllables, and when the syllables are stressed, as shown in Table 2.

Table 2. Consonant : Variations in tongue front contact

UTTERANCE IS IN FN R2 EF 72.57 58.38 64.48 0.012 GA 73.95 63.79 64.48 0.274

SYLLABLE 1st 2nd 3rd EF 71.46 60.50 62.87 0.174 GA 71.60 60.63 61.11 0.124

STRESS s u EF 67.64 63.59 0.029 GA 69.55 61.94 0. 062

The interactions among the three variables indicate that the effects of utterance, stress,

. and syllable position sum up, so that the high­est contact occurs in initial stressed syllables of isolated words (80.40 for EF; 84.07 for GA): in these cases it extends from Row1 (dental zone) to ROW 5 (postalveolar zone). The lowest contact occurs in the second or third unstressed syllables of embedded words (51.76 for EF; 41.95 forGA). ForGA we also observed a few cases of consonant deletion in syllable 2 of proparoxytone words. Hyper­articulation of initial consonants of isolated words does not seem to be related to their condition ofbeing absolutely initial. Compari­sons between the frrst and the second conso­nant in stressed syllables indicate that the relation between C 1 and C2 does not vary as a function of utterance (the ratio being 1.12, 1.15 1.26 (EF), and 1.11, 1.26, 1.11 (GA) for IS, IN and FN respectively. Comparisons between C2 and C3 indicate that C3 is not affected by fmal boundaries either in stressed or unstressed syllable.

3.3. The CV syllable The data indicate that stress and boundaries influence the whole syllable, while utterance type differences are signalled by the syllable for GA, and mostly by consonants for EF. Stress induces stronger effects on syllabic nuclei than on onsets, but the changes go in the same direction for both V and C. The pres­ence of stress, by enhancing the vowel-spe­cific distinctive properties, contributes to in­crease the phonetic distance among the three

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vowels. As for C, the increase in spatial ex­tent of closure in stressed syllables indicates that the consonant is produced with more ample gestures and possibly with greater force. Thus stress enhances both the differ­ences among vowels, and the contrast be­tween C and V. Consequently, stressed sylla­bles are expected to show a weakening of re­ciprocal CV coarticulatory effects. The sys­tematic increase in PI for stressed vowels (as compared to unstressed) indicates that their articulation is less influenced by the conso­nantal gesture. The coarticulatory V-to-C ef­fects were examined in word-initial syllables (in order to rule out the influence of V of the preceding syllable) with regression analysis, where TBCONT for Cs was regressed against TBCONT for the three vowels. The regres­sion coefficients resulted always significantly higher for unstressed than for stressed sylla­bles for EF, as expected (global results: RC stressed = 0.271; RC unstressed= 0.362). For GA coarticulatory effects in word-initial syl­lables were found to be very weak in both stress conditions, however also for this sub­ject the global trend is in the expected direc­tion (RC stressed=0.152; RC un­stressed=0.162). Also boundaries are signalled by an increase in CV contrast: initial boundaries are marked by a strengthening of consonant closure and by an increase in vowel posteriority (un­stressed V s are less reduced for GA); final boundaries are marked by an even greater vowel opening, which suggests a relaxation of the constriction. So it appears that the in­creased CV contrast at boundaries is brought about mostly along the high/low dimension, i.e. greater closing of Cs and/or greater open­ing ofVs.

4. Discussion and Conclusion The overall data indicate that the articulation of stress and the articulation of boundaries, both leading to an enhancement of CV con­trast, are brought about by different control strategies. The articulation of stress indicates that stressed syllable are characterized by a more distinct articulation of both C and V, which is compatible with the hyperarticula­tion hypothesis of de Jong [3], while the ar­ticulation of boundaries rarely implies a sharpening of vowel distinctiveness. This occurs for unstressed V s at initial boundaries only for subject GA. Final boundaries instead, are always characterized by a relaxation of the constriction for all vowels. Hence, glo­bally, the strategy underlying the production

of boundaries cannot be interpreted in terms of hyperarticulation. A recurrent vowel pa­rameter involved in the articulation of stress and boundary is PI: our hypothesis that Vari­ations in PI are associated with jaw height variations is supported by previous fmdings by Farnetani and Faber for one of these sub­jects [10], which clearly indicate that stressed Ii! and /a/ are produced with significantly lower jaw position than their unstressed Coun­terparts. The fact that boundaries for vowels are marked most exclusively by this param­eters suggests that in the strategy underlying the realization of boundaries, the major role is played by the rising and lowering of the jaw. The increase in CV contrast at bounda­ries could thus be accounted for by an increase in jaw height for Cs, and a further decrease in jaw height for V s.

References [1] Farnetani, E. and Vayra, M. (1991). Word­and phrase-level aspects of vowel reduction

·in Italian. Proc. XII ICPhS, Vol. 2, 14-17. [2] Moon, S.J. and Lindblom, B. (1994). In­teraction between duration, context, and speaking style in English stressed vowels. JASA 96, 40-55. [3] de Jong, K.J. (1995). The Supraglottal ar­ticulation of prominence in English. Linguis­tic stress as localized hyperaticulation JASA 97,491-504. [ 4] Beckman, M.E., Edwards, J.R., and Fletcher, J. (1992). Prosodie structure and tempo in a sonority model of articulatory dy­namics. In G. Docherty andD.R. Ladd (eds), Papers inLaboratory Phonology Il, CUP, pp. 68-86. [5] Edwards, J.R., Beckman, M.E., and Fletcher, J. (1991). The articulatory kinemat­ics offmallengthening. JASA 89, 369-382. [6] Fougeron, C. and Keating, P.A. (1995), Demarcating prosodic groups with articula­tion. JASA, 97, 5, 3384, A. [7] Keating, P.A. (1995). Segmental phonol-

. ogy and non-segmental phonetics. Proc. XIII ICPhS, Vol.3, 26-32. [8] Lindblom, B. (1990). Explainingphonetic variation: a sketch of the H&H theory. In W.J. Hardcastle andA. Marehai (eds), Speech Pro­duction and Speech Modelling, Kluwer Aca­demic Publishers (pp. 403-439). [9] Farnetani E. and Faber A. (1992). Tongue­jaw coordination in vowel production : Iso­lated words vs continuous speech. Speech Communication 11,401-410.