Phonological Features - Thesis

8/3/2019 Phonological Features - Thesis

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THE STABILITY OF PHONOLOGICAL FEATURES WITHIN

AND ACROSS SEGMENTS

THE EFFECT OF NASALIZATION ON FRICATION*

MARIA-JOSEP SOL

Universitat Autnoma de Barcelona

Abstract

This paper argues that the articulatory-acoustic stability of phonological featuresmay be affected not only by concurrent features, but also by features in adjacentsegments which may coincide in time due to coarticulatory overlap. Specifically,the paper illustrates how frication may be endangered by concurrent andcoarticulatory nasality. We review aerodynamic and acoustic evidence showingthat fricatives tend to be impaired and become unstable with co-occurringnasalization. Then we examine the stability of fricatives when they come incontact with nasality in adjacent segments. An experiment is described whereaerodynamic and acoustic data were obtained for fricative + nasal sequences atslow and fast rates. The results show that anticipatory velophrayngeal openingduring the acoustic duration of the fricative vents the high oral pressure requiredfor audible frication, thus providing support for the claim that the same physicalprinciples disfavoring the combination of frication and nasality within a segmentare at play when these features combine across segments. It is argued that theinstability of frication when combined with nasalization may be at the origin ofa number of phonological patterns.

1. Introduction

It is known that the articulatory-acoustic stability of phonologicalfeatures may be endangered by their combination with other features withinsegments. In this paper we suggest that the stability of features may be affectednot only by concurrent features, but also by features in adjacent segments

which may coincide in time due to coarticulatory overlap. Specifically, weexamine the stability of fricatives when they combine with nasality within asegment and when they come in contact with nasality in adjacent segmentswith varying degrees of coarticulatory overlap.

In this paper we focus on the phonetic grounding of the combination offeatures within a segment and across segments, and the implications for

* Work supported by grants HUM2005-02746, BFF2003-09453-C02-C01 from the Ministry ofScience and Technology, Spain, and by the research group 2005SGR864 of the CatalanGovernment. The insightful suggestions and comments of Daniel Recasens and an anonymousreviewer are gratefully acknowledged.


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THE STABILITY OF PHONOLOGICAL FEATURES 43

result. The quantal nature of speech has been illustrated by varying features inisolation along the articulatory (or acoustic) dimension and observing theacoustic/auditory result of such variations (e.g. laryngeal adduction and

presence of voicing; movement of the velum and percept of nasalization). Therange of allowable articulatory/aerodynamic variation within which the perceptof the feature is not affected will define the stability of the articulatory-acousticcorrelation.

Elaborating on this view, we may consider that this stable range mayvary, i.e. may be expanded, reduced, or shifted, with co-occurring features inthe same segment and, as claimed in this paper, in adjacent segments.Combinations of features which result in tightly constrained articulatory oraerodynamic requirements are unstable because they allow a narrow range ofvariation, that is, they may easily fall into a different category with small

variations in the articulatory/aerodynamic parameters. Such unstablecombinations may easily change into a different percept and will tend to bedisfavoured (as shown, for example, by gaps in segment inventories, and alower lexical frequency of certain segment types). A classic example is thedifficulty in maintaining the co-occurrence of voicing and obstruency. The

partial or full blockage of the air exiting the oral cavity for obstruents leads to arapid increase of oropharyngeal air pressurerequired to generate turbulencefor fricatives and to create an audible burst for stopsbut tends to impair thetransglottal flow required for voicing within a few tens of milliseconds. Unlessthe obstruent constriction is kept very short or the oral cavity is enlarged toaccommodate more air and thus prolong voicingboth maneuvers to the

detriment of a high pressure build-up for obstruencyvoiced obstruents willtend to devoice. Thus, voiced obstruents require very finely tuned aerodynamicconditions in order to maintain voicing and obstruency (Ohala 1983).Similarly, combinations of features which result in a poor acoustic signal, forexample voiceless nasals (as the low frequency amplitude modulation fornasals is impaired by voicelessness), are auditorily unstable (as measured fromconfusion studies) and will tend not to be used.

In order to describe the interactions between features it is necessary tovary the parametersphysiological, aerodynamic or acousticthatcharacterize such features not only singly but in combination (e.g. changes inoral pressure and duration of the obstruent constriction in the first example(Westbury & Keating 1986), or changes in glottal excitation for nasals andnon-nasals, or during different degrees of velopharyngeal opening for thenasal, in the second example). We can then identify a set of categorial valuesalong these parameters which remain stable with variations in the other

parameters. These categories or optimal settings across the different parameters, if wide enough in range, are the more likely combinations offeatures into segments.

The claim made in this paper is that the physical and auditory principlesthat account for how features interact within segments may also account for theinteraction of features in contiguous segments. It is known that when two


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segments are in contact their articulations necessarily overlap. Variations in theshape, position and temporal coordination of the articulators due tocoarticulation with neighbouring segments may cause modifications of the

articulatory trajectories or the aerodynamic conditions in the vocal tract thatcan, in turn, affect the acoustic and auditory result. Thus, the execution of thearticulatory gestures in implementing a particular feature will varyconsiderably with the features in contiguous segments. As described earlier,voicing is difficult to maintain during an obstruent; however, if an obstruent is

preceded by a nasal, voicing during the obstruent is facilitated. In nasal +obstruent sequences, voicing continuation into the obstruent is facilitated bynasal leakage before full velic closure is achieved and, after velic closure, bythe velum continuing to rise toward the high position for obstruents, thusexpanding the volume of the oral cavity. Both mechanisms, nasal leakage and

oral cavity expansion, lower the oropharyngeal pressure which accumulates inthe oral cavity and thus prolong transglottal flow for voicing (Hayes & Stivers1996). Such phonetic effects have phonological significance in languages witha phonological post-nasal voicing rule, in phonotactic patterns, and in soundchange. Thus, aerodynamic principles in the maintenance of voicing withinsegments may account for the extension (or cessation) of voicing whensegments are combined.

In order to test the hypothesis that the factors governing the interactionbetween features in the same sound may also govern the interaction of featuresacross segments when they overlap due to coarticulation, we designed a seriesof experiments to explore the impact of co-occurring and coarticulatory

velopharyngeal opening for nasality on the stability of segments requiring ahigh pressure build-up in the oral cavity, such as fricatives. The results maythrow light on why some feature combinations fail to occur, e.g. nasalfricatives, and why certain segment combinations, e.g. fricatives followed bynasals, tend to change. We report on research in which the aerodynamicconditions in these segment types were varied (1) by venting the oral pressurewith a pseudo-velopharyngeal valve, and (2) by increasing speaking rate andthus articulatory overlap of velopharyngeal opening on the pressure build-upfor the fricative.

The remainder of this paper is structured as follows. In Section 2 wereview the aerodynamic and perceptual effects of combining frication andnasalization within a segment. In Section 3 we address the conflictingrequirements of frication and nasalization when they occur in contiguoussegments and we review how fricatives tend to lose their friction precedingnasals historically and synchronically. In Section 4 we provide aerodynamicand acoustic evidence that in fricative + nasal sequences anticipatory velumlowering during the acoustic duration of the fricative reduces or extinguishesthe pressure difference required for frication. In Sections 5 and 6 we argue thatthe principles that explain why the features [nasal] and [fricative] do notcombine within a segment also explain why they do not combine acrosssegments.


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2. Co-occurring features: Nasality and frication

Languages of the world have nasal stops, nasal taps, nasal approximants,nasal glides and nasal vowels but no nasal fricatives (Ohala 1975; Ohala &

Ohala 1993). Segments reported as nasalized fricatives (e.g. in Umbundu(Schadeberg 1982), Coatzospan Mixtec (Gerfen 1999), and Waffa (Stringer &Hotz 1973)) are more adequately described as frictionless continuants due tothe lack of high frequency aperiodic noise (Ohala & Ohala 1993; Ohala, Sol& Ying 1998). The reported nasalized fricatives in Bantu languages, Kwalanguages, and Igbo appear to involve sequencing of the nasal and the fricativeconfiguration and are, in fact, better described as prenasalized fricatives(Welmers 1973:70-73).

Formal phonology attributes the lack of nasal fricatives to antagonisticconstraints: The rarity of such segments [nasalized liquids, glides and

fricatives] can be attributed to an antagonistic constraint NAS/CONT: A nasalmust not be continuant (Pulleyblank 1997:76); or to a constraint hierarchyranking segments according to their incompatibility with nasalization:*NASOBSTRUENTSTOP >> *NASFRICATIVE >> *NASLIQUID >>*NASGLIDE >> *NASVOWEL, where the less compatible a segment is withnasality, the higher-ranked its constraint (Walker 2000).

The phonetic grounding for such antagonistic constraints or constrainthierarchy is provided by work by Ohala and coworkers. Ohala and Ohala(1993) provide an explanation based on aerodynamic principles. They suggestthat obstruents require a build-up of oral pressure behind the constriction inorder to create audible turbulence. An open velopharyngeal port for nasality

would vent the airflow through the nasal cavity, thus reducing or eliminatingthe required pressure difference across the oral constriction for frication.Ohala, Sol and Ying (1998) further explored this explanation by examiningthe aerodynamic and acoustic effect on fricatives of concurrent nasality and its

perceptual result. They vented oro-pharyngeal pressure (Po) with a pseudo-velopharyngeal valve (i.e. catheters of varying cross-sectional areas: 7.9, 17.8,31.7, and 49.5 mm2; all 25 cm long, inserted into the mouth via the buccalsulcus and the gap behind the back molars), and quantified how muchvelopharyngeal opening for nasality was allowed before frication would beextinguished.

The results of Ohala et al. (1998) show that in producing a fricative therecan be some opening of the velic valve, but the impedance of this valve has to

be high relative to that in the oral constriction so that the air will escapethrough the aperture with lower impedance and create friction at the oralconstriction. Thus venting fricatives with catheters with a higher impedance(7.9 mm2-area catheter) than that at the oral constriction did not affect thequality of the fricative, it just slightly attenuated the fricative noise. Catheterswith values for impedance similar (17.8 mm2 area) to those at the oralconstriction had noticeable effects on fricatives: they lost much of their high-frequency aperiodic energy (e.g. the spectral peak at 6 kHz for [s] disappearedand the energy level dropped 20 dB). The effect was most dramatic for voiced


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fricatives, which became frictionless continuants. Sibilant fricatives soundednon-sibilant. Larger area catheters (31.7 mm2), with a lower impedance thanthat in the vocal tract, extinguished frication, since airflow exited through the

aperture with lower impedance, thus reducing the required pressure drop acrossthe oral constriction to generate turbulence. Voiceless fricatives only retainedthe glottal friction. Voiced fricatives were more seriously affected thanvoiceless fricatives, becoming vowel-like.

The results show that if impedance at the velopharyngeal port is lowerthan that at the oral constriction the air will escape through the nose (i.e. thefricative will be nasalized), but supraglottal frication will be impaired. Velicopenings which do not impair frication (


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noted by other investigators. For example, research on a variety of languageshas shown that nasalized voiced fricatives produced with perceptiblenasalization tend to lose audible frication and become approximants (e.g. in

Guarani, Gregores & Suarez 1967). In contrast, nasalized voiceless fricativeswith audible frication do not differ much auditorily from non-nasalizedfricatives, that is, the acoustic cues for nasalization are hardly detectable (Cohn1993; Ladefoged & Maddieson 1996:132).

0

20

40

60

80

100

0 10 20 30 40 50 60 70

velo-pharyngeal opening in mm2

%i

dentification

fricative nasalized

Figure 1:Diagrammatic representation of the reported percentage of identification of africative and a nasal for continuous variation in velic opening for a given flow rate. See text.

In the next section we address whether the weakening or loss of fricativesbefore nasals can be explained by the same principles.

3. Contiguous frication and nasality

Related to the difficulty of combining velopharyngeal opening withfrication within a segment is the precise timing of gestures in nasal + fricativeand fricative + nasal sequences if both segments are to be preserved. Theantagonistic requirements of turbulence generation (i.e. a tightly closed velumto allow turbulent airflow in the vocal tract) and nasal coupling (i.e. a loweredvelum) in contiguous fricatives and nasals severely constrain the timing ofvelic movements. The relative synchronization of articulatory movements innasal + fricative sequences has been investigated by Ali, Daniloff andHammarberg (1979), Ohala and Bus (1995), Ohala (1997b) and Bus (in

press) amongst others. Historically, such sequences may result in (i) nasalconsonant loss, with associated nasalization and lengthening of the precedingvowel (e.g. Latin institutione > Italian istituto; PGmc *fimf> Old Englishfive),and (ii) an epenthetic stop (e.g. EnglishHampstead,Hampshire < O.E. ham +

stede, scir). Interestingly, one or the other outcome has been related to specificcoarticulatory patterns (Bus in press). Ohala and Bus (1995) have argued thatthe first outcome, nasal consonant loss, is due to anticipatory vowelnasalization resulting from coarticulatory lowering of the velum for theupcoming nasal consonant and to associated perceptual factors. They provide

perceptual evidence that in these sequences the listener attributes the acoustic


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MARIA-JOSEP SOL48

effects of velum lowering for the nasal (attenuated amplitude and increased bandwidth of F1 in adjacent vowels) to the similar effects of a wide glottalopening required for high airflow segments, such as /s/, on neighboring

vowels, thus discounting the nasal consonant. The second outcome, epentheticstops, reflects anticipatory raising of the velum (and anticipatory glottalabduction) during the oral constriction for the nasal, which ensures sufficienttime and rate of flow to build up pressure for the fricative (Ali et al. 1979).

Reverse fricative + nasal sequences, although not the object of extensiveinvestigation, require equally precise coordination of velic and oral gestures.These sequences have resulted in several sound changes, including (i) fricativeweakening and loss2, and (ii) stop epenthesis. Importantly, the tendency forfricatives to weaken, or disappear, before a nasal may be related to thedifficulty involved in combining frication with velopharyngeal opening within

a segment observed in the preceding section. Examples of prenasal fricativeweakening in historical sound change, morphophonological alternations anddialectal-stylistic variation are shown in Table 1.

Prenasal fricative weakening may result in vocalization or gliding,rhotacism, nasal assimilation, and elision. Examples 1-3 and the first examplein (c) in Table 1 illustrate vocalization; 4 exemplifies rhotacism; 5-9 illustratefricative loss, and various examples of nasal assimilation and fricative loss are

presented in Section (c). The examples in (c) and the examples of /s/vocalization in (a) illustrate processes affecting only certain frequent words orcombinations of words, thus illustrating the role of frequency in phonologicalchange.

The weakening of prenasal fricatives in the Romance data in Table 1(a),examples 1-5, may be argued to be part of a more general historical process ofcoda weakeningdue to a drecreased oral gesture syllable finallyin LateLatin and Gallo-Romance (Straka 1964; Gess 1999) by which not onlyfricatives but also other obstruents were lost syllable finally, regardless of thenature of the following segment. We suggest that the weakening of fricatives

before nasals found in a variety of languages may be attributed not only toarticulatory reduction but more crucially to varying aerodynamic conditionsdue to the temporal sequencing of velic gestures.

Although fricative weakening in Romance also occurs before non-nasals(e.g. Latin insula island > French le; Germanic *bruzdon to embroider >Old Occitan broidar), a number of scholars (Pope 1934:151; Rohlfs 1966;Torreblanca 1976; Recasens 2002) have noted that this process is favored by afollowing voiced consonant and, in particular, by a following [n], [m], [r] or

2 The term fricative weakening is used here to indicate attenuation of the high frequencynoise which characterizes fricatives, due to gestural reduction or aerodynamic factors. Fricativeloss is considered the endpoint of the weakening continuum, i.e. extreme attenuation leading tothe segment becoming inaudible. In perceptual terms gradient attenuation of the friction noisemay result in identification of a discrete segment (e.g. a frictionless continuant, a vowel, a tap,an assimilated segment, or /h/) or in the perceptual loss of the segment (i.e. deletion).


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[l]3. Recasens (2002:342) attributes fricative weakening before voicedconsonants in general to anticipatory glottal gestures for voicing during thefricative, which result in reduced transglottal flow (due to higher glottal

impedance) and lower intensity of frication vis--vis pre-voiceless fricatives,thus making frication more likely to be missed. Other factors besides voicing,however, may be at play in the common weakening of fricatives precedingnasals, laterals, and trills. Fricative weakening may arise from variation in therelative timing of antagonistic positional requirements of the tongue forcontiguous lingual fricatives and laterals (raised tongue sides and centralcritical constriction for the fricative and lowered tongue sides and centralcontact for the lateral; Ohala 1997b), and lingual fricatives and trills (raisedand advanced tongue dorsum and a central groove for /s/ vs predorsumlowering and postdorsum retraction with a lax tongue-tip for the trill; Sol

2002b); in such sequences anticipatory movements for the lateral or the trillmay bleed the positional and aerodynamic requirements for audible fricationfor [z, s]. In a similar way, in fricative + nasal sequences variation in therelative timing of the velic opening gesture and the preceding oral constrictionfor the fricative (requiring a sealed velum) may result in fricative weakening.In particular, anticipatory velum lowering for the nasal may affect theaerodynamic requirements for the generation of turbulence for the fricative.

The examples in Table 1 illustrate that fricatives are weakened intofrictionless continuants, or are lost altogether, more often when followed by anasal segment, involving the same or different articulators, than when followed

by non-nasal segments, when they retain their fricative quality. Fricatives have

also been found to disappear in connected speech in French before nasalvowels (D. Duez, p.c.), which involve a lower position of the velum than nasalconsonants. Consonants other than fricatives may assimilate the velic state ofthe upcoming nasal in casual speech (e.g. let me [lemm], wouldnt [wnnt],Gimson, 1962), but they do not result in sound change or phonologicalalternations4. The question is then why fricatives are weakened more oftenthan other segment types, and why they are weakened more often before nasalas opposed to non-nasal sounds.

We hypothesized that the same aerodynamic factors disfavouring thecombination of frication and nasality within a segment are responsible for theweakening/loss of fricatives before nasals: anticipatory movements to lowerthe velum for the nasal may reduce the oropharyngeal pressure necessary forthe generation of turbulence for the fricative. Coarticulatory nasal leakage

3 Thus, for example, in Old French /s/ weakening and loss is found earlier in blmer< blasmer< Lat. *blastemare blame and mler< mesler,medler[l] < Lat. misculare meddle than infte


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would have a larger effect on voiced fricatives as opposed to voicelessfricatives (Ohala et al. 1998; Sol 2002b), since to generate friction at the oralconstriction while air is flowing out through the nasal passage due to

anticipatory velopharyngeal opening would require a high volume of flow, andvocal fold vibration reduces airflow through the glottis. Thus, voiced fricativeswith overlapping velic movements for the nasal would have two independentsystems reducing the pressure drop across the oral constriction required forfrication, high impedance to ingoing airflow at the glottis and low impedanceto outgoing flow at the velum. In addition, voiced fricatives are known to beshorter than voiceless fricatives and, due to the lesser rate of flow through thevibrating glottis, they take longer to achieve the pressure difference forfrication and result in a lower intensity of friction than their voicelesscounterparts (Sol 2002b). This makes anticipatory velopharyngeal opening for

the nasal more likely to impair audible friction in voiced than in voicelessfricatives. This prediction is in accord with the fact that the majority ofexamples of fricative weakening in Table 1 involve voiced fricatives.

Note that our aerodynamic and perceptual explanation is not at odds withOhala and Buss (1995) claim presented above that in N + fricativesequences, the nasal disappeared due to acoustic-perceptual factors. The N +fricative sequences they examine (e.g. Latin institutione > Italian istituto), infact, illustrate that anticipatory velum lowering can be accommodated by a

preceding vowel, nasalizing it, and that the acoustic effects of nasalization onthe vowel may be misidentified. What we suggest is that in fricative + Nsequences nasalization cannot be accommodated by a preceding fricative

without compromising its spectral identity. The active role of the listener herewould involve reconstructing a frictionless continuant at face value (forexample, [j], [w] or a rhotic) or missing the fricative altogether.

A second outcome of contiguous fricatives and nasals (which require atightly closed velum and a lowered velum, respectively) is an epenthetic stop inthe transition between the two articulatory configurations, due to a prolongedvelic occlusion of the fricative during the oral constriction for the nasal (e.g.Old English glisnian > glisten; Sanskrit krsn > Krishna ~ Krishtna). Alongsimilar lines, the insertion of an epenthetic schwa in /sm/ >[sm] and /sn/ >[sn] sequences in Montana Salish (Ladefoged and Maddieson 1996:109-110)reflects a delayed velic lowering and oral closure for the nasal relative to theend of the fricative (i.e. an increase in the temporal distance betweenarticulatory gestures), which avoids an overlapped lowered velum during thefricative in order to preserve frication. Thus a very precise synchronization ofthe velic and oral movements is required in order to sequence segmentsinvolving frication and nasality.


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(a) Historical change

1. [zn], [zm] > [jn], [jm] Latin mesnata kids, elemos(i)na alms > Catalan mainada,

almoina (Badia 1951).Latin asinu donkey > Gascon aine (cited in Recasens 2002).

Standard Catalan besntgrandchild > Majorcan Catalan beint.Old French ae(s)mer, Standard Catalan esma > Majorcan Catalan eima(Alcover & Moll 1978-1979); English aim.

2. [n] > [jn], [wn] Latin agnu lamb, ligna line > S. Italian dialects ['ajn], ['lwna] (citedin Recasens 2002).

3. *[dzm], *[m] > [wm] Latin decimare, decimu > Catalan deumarlessen, reduce, deumetribute.

4. [zn], [zm] > [n], [m] Latin asinu donkey > Old Picard arne.Latin *dis(ju)nare to eat breakfast > Old Occitan dis/rnar(also Cat. dinar).Latinspasmu spasm > Roussillon esparme (cited in Recasens 2002).

S. Spanishmismo

['mimo

] same (Recasens 2002).

5. [zm] > [m] Old French ble(s)mir> English blemish.Vulg.Latin blastemare > Old French bla(s)mer> Fr. blmer, English blame.

Latin rosmarinu, -aris > *romarinu, -ari(u)s rosemary > Catalan roman,

Spanish romero.

Standard Catalan quaresma Lent > Majorcan Catalan [ko'm].

6. *sn > [n] IE snus daughter-in-law, OE snoru > Latin nurus, Greeknus, Armeniannu, Spanish nuera (Watkins 1985).

7. *sn > [n] Burmese *sna > [na] nose.

(b) Phonological alternations

8. [sn] > [n] IE *dhus-no > Welsh dwn dull, brown colour, OE dun(n) dark brown;BUT IE *dhus-ko > Latinfuscus, OE dox, English dusk(Watkins 1985).

IE *dhs-no > Latinfanum temple, Englishfanatic, (pro)fane;

BUT IE *dhes-to > Lat. festus festive, German Fest, Spanish fiesta; IE

*dhes-ya> Lat.fesiae, feriae, Englishfair, Spanishferia (Watkins 1985).

9. [sm] > [m] IE *gras-men > Latingramen fodder, Englishgrama, gramineous;BUT IE *gras-ter > Greekgasterstomach, English gastric, epigastrium(Watkins 1985).

(c) Stylistic variation

[zn] > [nn], [jn] isn't[nnt], aint [ent]; doesnt[dnnt]; wasnt[wnnt] (Gimson 1962).

[mV

n] > [mn], [mn]something[smn], [smn].

[nsVn] > [nVn] Vincent that[vnn] Tyneside English (Local 2003:325).

[mfrVn] > [mrVn] San Francisco [smrnssko] American English (N. Hilty, p.c.).[vm] > [mm] give me, gimme [mm], have mine [hmman] (Gimson 1962).

[VN] > [VN] like them [lakm],tell them [telm].BUT like this [lak s], tell this [tel s].

[VN] > [VN] thank you, thanks [kju], [ks].[zn] > [nn] business [bdns], [bnns].

Table 1:Examples of fricative weakening/loss in fricative + nasal sequences.


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4. Experiment. Variations in articulatory overlap

The following experiment was designed to find out whether the tendencyfor prenasal fricatives to weaken or disappear can be attributed to anticipatory

velopharyngeal opening for the nasal overlapping the acoustic duration of thefricative, thus diminishing the oropharyngeal pressure required for frication, asargued for concurrent features. In order to test this hypothesis we examinedwhether anticipatory velic opening occurred in such sequences and, if so, howit affected the aerodynamics and acoustics of fricatives.

4.1 Experimental procedureSimultaneous oropharyngeal pressure (Po), oral and nasal flow, and audio

signal were obtained with PCquirer (Scicon) for five American Englishspeakers producing words containing fricative + nasal sequences at slow and

fast speech. The two speaking rates allowed us to observe the effects ofincreased articulatory overlap on the relative timing of velic and oral gestures,and how such changes in timing affect the pressure build-up for fricatives. Theaudio signal was digitized and sampled at 12 kHz, and the dc channels weresampled at 1 kHz. Po was obtained by a catheter introduced at the side of themouth and bent behind the rear molars and connected to a pressure transducer.The volume flow from the mouth and the nose was collected simultaneouslywith a Rothenberg mask, using one of the outlet holes in the mouth mask forthe pressure tube. The pressure and airflow signals were low-pass filtered at 50Hz. Po and airflow were calibrated as described in Sol (2002a). Wordscontaining fricative + nasal sequences with C1 = [s, z] and C2 = [n, m] in

word medial position (e.g. Dessna [desn], Fresno [frezno], Missmer[msm], Mesmer[mezm]) were read in a carrier phrase. Control sequenceswith voiced and voiceless alveolar fricatives followed by laterals, stops,fricatives and approximants, all dento-alveolar (e.g. Grizzly[zl], Gizder[zd], isthe [z], Ezra [z]; Esling [sl], Esda [sd], less the [s], Esra [s]) were alsoanalyzed for comparison. The test and control tokens were randomized in thereading list.

The aerodynamic and acoustic data were collected in two differentsessions. In the first session, three speakers (JO, MS and DM) read fiverepetitions of each token at self-selected slow and fast rates. Because the threespeakers showed different patterns of velic-oral coordination, two morespeakers were recorded in a second session under the same conditions.Speakers JE and RS produced six repetitions of each token at slow and fastrates.

4.2 Measurements and analysisThe measurements made on the data are illustrated in Figure 2, which

shows the aerodynamic and acoustic data for Say Mesmer again in slow andfast speech for one of the speakers. Measurements were made at the following

points in time for the fricative + nasal sequence: onset and offset of friction onthe spectrographic records; onset of increased nasal flow (channel 5), indicated


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by a vertical line in Figure 2, reflecting velo-pharyngeal port opening for thenasal /m/; onset of oral closure for the nasal, indicated by a drop in oral flow(dotted line in channel 4), and offset of the nasal, indicated by an increase in

oral flow (dashed line in channel 4) and an increase in amplitude and formantstructure for the following vowel on the spectrogram. Figure 2 illustratesanticipatory velopharyngeal opening: the vertical lines mark the onset of nasalflow (channel 5) due to velum lowering for the nasal. At this point in time oral

pressure decreases (channel 2) and the high frequency noise disappears (inslow speech) or is attenuated (in fast speech) (The sliding center frequencynoise after the vertical line in fast speech reflects the effect of anticipatory lipmovement, which is known to filter out higher frequencies). The increase innasal flow leads the drop in oral flow (dotted line in channel 4) for thecomplete oral constriction for the nasal. Thus, for a few tens of ms there is

concurrent (increasing) nasal flow and (decreasing) oral flow, characterisedacoustically by some low amplitude aperiodic noise around 3 kHz. In otherwords, the velum starts to lower during the acoustic duration of the fricative,resulting in a sudden drop in amplitude of high frequency noise.

SLOW FAST

[ s e m e z m e n] [ s e m e z m e n]

Figure 2: (1) Audio signal, (2) filtered Po, (3) unfiltered Po, (4) oral airflow, (5) nasal airflowand 0-5 kHz spectrogram ofSay Mesmer again in slow and fast speech. Speaker JO. See text.

The duration of fricatives in test and control sequences was measured onspectrograms and aerodynamic records. In fast speech a considerable numberof cases involved blending of the gestures for the two contiguous consonantsgenerally resulting in deocclusivized following stops (as noted by Honorof2003) or fricativized following sonorants [l, r, n, m]. The aerodynamic recordswere of great help in segmenting these blended sequences.


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4.3 Results4.3.1 Patterns of velic movements. The patterns of velic coordination observedin the data are described in patterns 1 through 4, below, and schematized in

Figure 3, which shows the oral gestures for the fricative (C1) + nasal (C2)sequence followed by traces of the observed velic patterns. Time 0 is the onsetof the oral constriction for the nasal, indicated by the drop in oral flow (dottedline in Figure 2). A delayed oral gesture for the nasal, resulting in an epentheticvowel, is represented at the bottom of Figure 3.

(1) If onset of velopharyngeal opening is synchronized with the oralconstriction for the nasal, nasal flow starts at 0. We take this pattern toreflect a precise synchronization of the supraglottal and velic gesturesfor the nasal5, which allows sequencing of the fricative and the nasal

consonant.The oral and velic gestures for the nasal, however, may not be preciselysynchronized.

(2) Onset of velum opening, i.e. nasal flow, may occur prior to the completeoral constriction for the nasal (time 0). That is, anticipatoryvelophrayngeal opening overlaps the acoustic duration of the precedingfricative. In this case we find concurrent oral flow (from the fricativeslit constriction) and nasal flow before time 0 in the aerodynamic data,and lack of friction or attenuated friction on the spectrogram during thistime interval.

(3) Velopharyngeal opening may be delayed relative to the oral constrictionfor the nasal (time 0) resulting in a transitional epenthetic stop. In thiscase the aerodynamic data shows neither nasal flow (velum up) nor oralflow (nasal constriction formed) immediately after 0, and a silent gapon the spectrogram. We found the epenthetic stop to be audible if theoral and velic closure overlapped for over 15 ms. Figure 3 shows thatthe transitional stops emerging in these sequences are always nasallyreleased, that is, they end when the velum lowers.

(4) Finally, the oral constriction for the nasal may be delayed with respect tothe release of the preceding fricative constriction, resulting in anepenthetic vowel. In this case oral and nasal flow is found immediately

before 0. Only one such case was found in the data.

5 Whereas it is clear that the oral target gesture for the nasal is a complete constriction, thevelic target gesture may not be opening the velum but rather achieving a certain magnitude ofvelum opening. If this were the case, onset of the oral closure for the nasal would becoordinated with a lowered velum, and nasal flow would begin before 0, as in the case in VNsequences. However, since most of the observed values cluster around 0, we will assume thesuggested target coordination.


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It is worth noting that these patterns parallel those found in the historicaland synchronic data reviewed in Section 3, in line with Ohalas (1989, 1993)claim that sound change emerges from synchronic phonetic variation.

1. synchronous, onset of nasal flow at 0

2. bleeding Po, oral & nasal flow before 0

3. epenthetic stop, no nasal or oral flow after 0

4. epenthetic vowel, oral & nasal flow before 0

Figure 3: Diagrammatic representation of patterns of velic coordination in fricative-nasalsequences. Traces for the supraglottal movements for C1 and C2 followed by different traces

of velum position (dashed lines). See text.

4.3.2 Coordination and timing of velic movements. The patterns ofcoordination of oral and velic movements in fricative + N sequences for eachtoken at slow and fast rates are presented in Figure 4. This figure plots the timeinterval between onset of velopharyngeal opening and onset of the oralconstriction for the nasal (time 0) for each token for the five speakers. The

production of each individual token has been arranged in decreasing durationof that interval. Bars to the left of 0 are cases of anticipatory velopharyngealopening (onset of nasal flow precedes onset of oral constriction for the nasal;

pattern 2 in Figure 3); tokens at 0 represent synchronous onset of oral and velicgestures for the nasal (onset of nasal flow at 0; pattern 1 in Figure 3) and,consequently, a precise sequencing of the fricative and the nasal segment; bars

to the right of 0 represent cases of velopharyngeal opening lagging behind theoral closure for the nasal (transitional stops; pattern 3 in Figure 3). The singlecase of vowel epenthesis (Fresno pronounced [frezno]), where the oralconstriction for the nasal consonant is delayed relative to fricative release andvelum lowering, is indicated by a lined bar (speaker DM, slow speech). Sinceinspection of the patterns of sequences involving voiced (e.g. Fresno) andvoiceless (e.g. Dessna) fricatives showed no differences, both types ofsequences were pooled in this graph. White bars represent homorganicsequences, [sn, zn], and grey bars represent heterorganic sequences, [sm, zm].Each bar represents one token and the number of plotted tokens ranges


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MARIA-JOSEP SOL56

between 5-6 for each sequence, [sn, zn, sm, zm], depending on the speaker andsession.

Figure 4 shows that although all observations cluster around time 0, the

five speakers show three distinct patterns of velic-oral coordination. Subject JOexhibits extensive anticipatory velic opening during the acoustic duration ofthe fricative for homorganic and heterorganic sequences. Such anticipatoryvelic opening vents the required high oral pressure for turbulence and, thus,frication is attenuated or extinguished (see Figure 2). Speakers JE and MSexhibit a majority of cases of anticipatory velic opening in heterorganicsequences (/sm, zm/), but not in homorganic sequences (/sn, zn/), which exhibita greater number of transitional stops (i.e. delayed velum lowering)6. However,

both speakers show cases of a precise synchronization (time 0) and ofanticipatory velic opening for homorganic as well as heterorganic sequences.

Finally, speakers DM and RS show mostly epenthetic stops, with a few casesof anticipatory velopharyngeal opening. The difference between homorganicand heterorganic sequences for these speakers seems to point in a differentdirection from that observed for speakers JE and MS: the epenthetic stops,resulting from a prolonged velic raising while the oral occlusion for the nasalhas been achieved, appear to be more common and longer for /sm, zm/sequences than for /sn, zn/ sequences. In spite of speaker-dependentdifferences, all speakers show cases of anticipatory velic opening bleeding thehigh oral pressure for frication. Overall, anticipation of velar activity during thefricative was found in 40% of the tokens in slow speech and 26% of the tokensin fast speech.

We now turn to differences in the timing of gestures in slow and fastspeech. We expected to find greater overlap of anticipatory movements of thevelum with the fricative in fast vis--vis slow speech. Contrary to ourexpectations, Figure 4 shows similar patterns of coordination of velic and oralgestures at slow and fast rates for each speaker, and no major differences in theabsolute values of velic timing across rates. Any differences are in the directionof more cases (i.e. more bars with negative values) and a longer period (i.e.larger negative values) of anticipatory velic lowering in slow than in fastspeech. That is, the velum appears to be freer to lower before the oralconstriction for the nasal is achieved at slow rates, most likely due to the time

pressure in fast speech imposing tighter time constraints. However, sincefricatives are slightly shorter at faster rates, the same period of anticipatoryvelopharyngeal opening has a slightly greater percentage effect in fast than in

6 Assuming that the motor instructions for the oral and velic gestures for the nasal aresynchronic, and ignoring differences in velocity of articulators, the difference betweenhomorganic and heterorganic sequences could in part be accounted for in terms of gesturesinvolving independent articulators overlapping in timeanticipatory overlap of the labial andvelic gesture for /m/ during the alveolar fricative in /sm, zm/ sequences.In homorganic /sn, zn/sequences involving the same articulatorthe tongue tipthe oral and velic gestures for thenasal would be delayed till the tongue tip was available for repositioning. However, thisinterpretation does not explain why velic opening lags behind the oral closure for the nasal inhomorganic sequences.


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7slow speech. This is illustrated in Figure 5, which plots the modal duration ofanticipatory velopharyngeal opening found for each speaker and rate as a

percentage of the average duration of the fricative for that speaker and rate, for

voiced and voiceless fricatives separately. Figure 5 shows a slightly largerpercentage of overlapping velopharyngeal opening (i.e. longer black bars) infast than in slow speech for all speakers and sequences. Figure 5 also allows usto observe the larger percentage of anticipatory velopharyngeal opening invoiced as opposed to voiceless fricatives, due to the shorter duration of theformer.

SLOW FAST

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7 The mode was plotted rather than the mean because of extreme values in the data.


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Figure 4: Coordination of oral and velic gestures for each production ofFresno andDessna(white bars), andMesmerandMissmer(grey bars) at slow and fast rates for each speaker.

Tokens with voiced and voiceless fricatives have been pooled.


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fricative duration overlapped velopharyngeal opening

Figure 5: Modal duration of anticipatory velopharyngeal opening (heterorganic andhomorganic sequences pooled) as a percentage of the total duration of the voiced or voiceless

fricative in slow and fast speech for the five speakers.

4.3.3 Fricative duration. The hypothesis that nasal leakage due to anticipatoryvelopharyngeal opening extinguishes or attenuates frication for a few tens ofms predicts that fricatives preceding nasal or nasalized segments should be

phonetically shorter than those preceding non-nasal segments. We tested this prediction by measuring fricative duration for test and control tokens in slowand fast speech.

The results of the measurements show that, as predicted, fricatives preceding nasals are generally shorter than those preceding non-nasals.(Following fricatives and laterals also tend to result in shorter precedingfricatives for some speakers.) Two-way ANOVAs with fricative voicing(voiced, voiceless) and following consonant (nasal, non-nasal) as independentvariables, and duration of the fricative as the dependent variable, were

performed for each speaker and speech rate separately. Table 2 shows theresults for the ANOVAs. The durational differences between fricatives

preceding nasal vs non-nasal consonants reached significance for speakers JO,MS and DM in slow and fast speech. Since the interaction between the twofactors was significant for speaker JE at faster rates, one-way ANOVAS were

carried out for voiced and voiceless fricatives separately for this speaker.Voiced fricatives were found to be significantly shorter preceding nasal thanoral consonants (F(1,33) = 11.629, p


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MARIA-JOSEP SOL60

JO JE MS DM RSSlow speechPrenasal vs

non-prenasal

F(1,76)=82.76,

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effect at faster rates due to the slightly shorter duration of the fricative in fastspeech.

The results in Section 4.3.2 also show cases of epenthetic stops in the

transition between fricatives and nasals due to prolonged velum raising for thefricative when the oral constriction for the nasal has been achieved. Suchtransitional stops are always nasally released and the lack of a strong release

burst, which is a perceptual cue for intrusive stops (Ali et al. 1979), is mostlikely the reason why these epenthetic stops may not be noticed by speakersand have not phonologised as opposed to those emerging in contexts wherethey are orally released (e.g. nasal + fricative, sense [nts]; nasal + flap, Catalancambra < Latin cam(e)ra; nasal + lateral, Spanish temblar< Latin trem(u)lu;lateral + fricative, else [lts]). Finally, the results in Section 4.3.3 show that theduration of the fricative tends to be shorter preceding nasal than oral

consonants, suggesting that the effect of nasal leakage during the latter portionof the fricative is present phonetically.The results obtained are compatible with the proposed account for the

historical and synchronic defricativization or loss of fricatives before nasal ornasalized segments: velopharyngeal opening during the latter part of thefricative vents the intraoral pressure, thus reducing or eliminating the required

pressure difference across the oral constriction for audible frication. Thesefindings suggest that interarticulatory timing and associated aerodynamiceffects may account for weakening of segments crucially dependent on airflowconditions. Indeed, data on the perceptual impact of these aerodynamic andtemporal variations is needed to back up the findings of this study.

6. General conclusions

We set out to test the hypothesis that the physical and physiological principles used to account for paradigmatic aspects of phonology, such asfeature co-occurrence restrictions, can be used to explain syntagmatic aspects,such as phonotactic patterns, context-dependent phonological processes andsound change. The results of the experiments reported here show that speechfeatures requiring high airflow through the oral constriction, such asfricatives8, tend to be impaired and become unstable with co-occurring orcoarticulatory nasalization. The results in Section 2 show that a reduction inoral pressure during the articulation of a fricative (due to venting oral pressurewith a pseudo-velopharyngeal valve) reduces the pressure difference and the

particle velocity of the air across the oral constriction, and frication isattenuated or losthence, the constraint against combining the features[fricative] and [nasal] within a segment. The results of the experiment inSection 4 show that when these features occur in contiguous segments, as infricative + nasal sequences, there can be anticipatory velopharyngeal openingduring the acoustic duration of the fricative, which has the same aerodynamic

8 Tongue-tip trills also require high airflow to set the tongue tip into vibration and,consequently, cannot be nasalized. For the incompatibility between trilling and nasality seeSol (2002b).


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MARIA-JOSEP SOL62

and acoustic consequences on the fricative as concurrent nasalization.Reduction of the oral pressure and subsequent reduction of the intensity of thehigh-frequency noise may lead to a non-fricative percept or to missing the

fricative altogether. Thus, the same factors responsible for the difficulty incombining the two features within a segment may be used to explain why thesefeatures do not combine across segments. Relating constraints on thecombination of features within and across segments illustrates the generalitythat can be achieved by a physically based explanation.

The instability of frication when combined with nasalization may be atthe origin of a number of phonological patterns, specifically, feature co-occurrence restrictions (e.g. lack of nasal fricatives), phonological change,morphological alternations and stylistic variation (e.g. loss/weakening offricatives followed by a nasal), and transitional probabilities in the sequencing

of sounds (lower lexical frequency of fricatives followed by nasals, Sol(forthcoming)). This is one further example of how phonological structure mayemerge from physical constraints as advocated by Ohala (1974, 1983) andLindblom (1986, 1990), and strongly suggests that the same physical principlesmay provide an explanation for paradigmatic and syntagmatic aspects of

phonology.

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