Cutler, A.

Pallier, C.

Sebastian-Galles, N.

NARCIS 

Prosodic structure and phonetic processing : A cross-linguistic study

Dutch and Spanish differ in how predictable the stress pattern is as a function of the segmental content: it is correlated with syllable weight in Dutch but not in Spanish. In the present study, two experiments were run to compare the abilities of Dutch and Spanish speakers to separately process segmental and stress information. It was predicted that the Spanish speakers would have more difficulty focusing on the segments and ignoring the stress pattern than the Dutch speakers. The task was a speeded classification task on CVCV syllables, with blocks of trials in which the stress pattern could vary versus blocks in which it was fixed. First, we found interference due to stress variability in both languages, suggesting that the processing of segmental information cannot be performed independently of stress. Second, the effect was larger for Spanish than for Dutch, suggesting that that the degree of interference from stress variation may be partially mitigated by the predictability of stress placement in the language

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Prosodic structure and phonetic processing: A cross-linguistic study

Pallier, Christophe

Cutler, Anne

Sebastian-Gallés, Nuria

CogPrints Cognitive Sciences Eprint Archive

Radboud Repository

PROSODIC STRUCTURE AND PHONETIC PROCESSING:A CROSS-LINGUISTIC STUDYChristophe Pallier1,2, Anne Cutler1 and Núria Sebastián-Gallés21Max-Planck-Institute for Psycholinguistics, Nijmegen, The Netherlands.2Departament de Psicologia Bàsica, Universitat de Barcelona, Spain.E-mail : pallier@lscp.ehess.frABSTRACTDutch and Spanish differ in how predictable the stresspattern is as a function of the segmental content: it iscorrelated with syllable weight in Dutch but not inSpanish. In the present study, two experiments were runto compare the abilities of Dutch and Spanish speakers toseparately process segmental and stress information. Itwas predicted that the Spanish speakers would have moredifficulty focusing on the segments and ignoring thestress pattern than the Dutch speakers. The task was aspeeded classification task on CVCV syllables, withblocks of trials in which the stress pattern could varyversus blocks in which it was fixed. First, we foundinterference due to stress variability in both languages,suggesting that the processing of segmental informationcannot be performed independently of stress. Second, theeffect was larger for Spanish than for Dutch, suggestingthat that the degree of interference from stress variationmay be partially mitigated by the predictability of stressplacement in the language.1. INTRODUCTIONThe prosodic and segmental dimensions of speech arefully integrated in the speech signal. Any prosodiccontrast between two signals is realised via changes inhow the segments are uttered — with longer or shorterduration, greater or lesser amplitude, more or less pitchmovement, for example. Yet recent studies from anumber of different languages have suggested that theprocessing of prosodic structure in the form of stress is tosome extent independent of the processing of segmentalstructure. Thus lexical access by English listeners doesnot appear to take into account stress distinctions, of thekind that differentiate between word pairs such as 'trustyand trus'tee [1]; similar results with such word pairs alsoappear in Dutch [2]. French listeners ignore accentdifferences when making similarity judgments aboutnonwords [3].The selective attention paradigm [4] offers a powerfulmeasure of whether two dimensions of an auditory signalmay or may not be processed independently. In this tasklisteners categorise stimuli on the basis of one auditorydimension; the independent variable is the presenceversus absence of variation in another dimension,notionally irrelevant to the categorisation task. Withsimple CV syllables, classification of segments is slowedby irrelevant variation in the syllable's pitch [5-8],suggesting that the processing of segmental informationand of at least one type of prosodic information are notindependent. In the present study we used the selectiveattention task to investigate the processing of stress andsegmental structure in CVCV bisyllables. If the resultsfrom simple pitch variation are representative of all typesof prosodic information, then stress variation will alsointerfere with segmental decisions; but if higher levels ofprosodic structure such as stress (which requires apolysyllabic domain for contrasts to be displayed) areindeed processed independently of segmental structure,as the results summarised above seem to suggest, then wewill observe no such interference.We carried out the comparison in two languages, whichboth exhibit stress contrasts, but differ in the degree ofdependence between the prosodic and segmentalstructure of words. In Dutch, stress contrasts are usuallyaccompanied by contrasts in syllable weight, wherebystress is assigned to the heavier syllable. In Spanish,bisyllables in which the two syllables have equal weightare much more common. Since the placement of Dutchstress is thus generally more predictable than theplacement of Spanish stress, we may expect thatsegmental judgments are more likely to be independentof stress variation in Dutch than in Spanish.2. EXPERIMENT 1: SPANISH SUBJECTS2.1 Method2.1.1 MaterialsThe pseudowords deki and nusa were chosen as stimulifor the experiment; both would make phonologicallyacceptable lexical items in Spanish or in Dutch. OneSpanish speaker and one Dutch speaker recorded twotokens of both deki and nusa: one with the stress fallingon the first syllable, and the other with the stress on thesecond syllable. Thus, there were four Spanish items andfour Dutch items ('deki, 'nusa, de'ki and nu'sa). Thesestimuli were digitized at 16 Khz and stored on the harddrive of a PC computer.2.1.2 ProcedureEach subject was tested in an individual booth, facing aPC that controlled the presentation of the stimuli andmeasured the response times, using the software EXPE[9].The task was speeded classification. Each trial startedwith the auditory presentation of a stimulus which thesubject had to identify. She indicated her response bypressing one of two buttons corresponding respectivelyto deki and nusa (irrespective of the stress position). Shehad a 1500 msec time window (starting at stimulus onset)to do this, after which feedback was displayed for 800msec: if the decision was correct, the reaction time fromstimulus' onset was given, whereas in case of an incorrectresponse (or no response), the mapping of stimuli toresponse keys was presented on the screen. The screenwas then cleared for one second, and the next trialstarted.The experiment consisted of blocks of 64 trials. Therewere two types of blocks: "Varied" blocks where the fouritems ('deki, 'nusa, de'ki, nu'sa) appeared and where thestress pattern could thus vary from trial to trial; and"Fixed" blocks where only two items (e.g. 'deki or 'nusa)were used as stimuli and where the stress pattern wasconstant. All the items in a block belonged to the samelanguage, Spanish or Dutch.After a practice block with sixteen trials and four stimuli,each subject was presented with four experimentalblocks: two "varied" and two "fixed" blocks. Among the"fixed" blocks, one contained the items with initial stresswhile the other contained the items with final stress. Theorder of blocks was counterbalanced across subjects anda given subject heard only stimuli from one language(Spanish or Dutch). In other words, half the subjectswere assigned to the Spanish material and the other halfto the Dutch material. The order of items in a block wasrandomized for each subject.2.1.3 SubjectsSixty-four native speakers of Spanish, all students fromthe university of Barcelona, participated in theexperiment in exchange for course credits.2.2 ResultsMean response times and error rates are displayed inTable 1. An analysis of variance on the response times,which crossed the factors Stress (Varied vs. Fixed) andLanguage of the stimuli (Spanish vs. Dutch), revealed asignificant effect of Stress (F(1,56)=64; p<.0001) whichinteracted with the Language of the stimuli (F(1,56)=8.8;p<.01). One-way ANOVAs of the Spanish and Dutchstimuli separately showed that the effect of Stress wasnevertheless significant in both cases (Spanish:F(1,28)=14; p<.001; Dutch: F(1,28)=54; p<.0001). Asimilar ANOVA on error rates yielded no significanteffect.Table 1: Mean classification times (in ms) and errorrates of Spanish subjects.Stress patternFixed Varied DifferenceStimuliSpanish 432 / 3.0% 447 / 2.7% 15 / -0.3%Dutch 444 / 2.7% 476 / 3.1% 32 / +0.4%Spanish subjects clearly show the interference effect; thatis, they are significantly slowed down by the stressvariability. The effect is larger for the stimulipronounced by a foreign speaker.3. EXPERIMENT 2: DUTCH SUBJECTSStress is more predictable in Dutch than in Spanish. WillDutch subjects be better able than the Spanish to ignorethe stress variations and focus on the segments? Toinvestigate this question, we replicate the previousexperiment with Dutch subjects.3.1 Method3.1.1 Material & ProcedureThe same materials, procedure and design as inexperiment 1 were employed.3.1.2 SubjectsFifty-six subjects from the pool of subjects of the Max-Planck-Institute for Psycholinguistics, in Nijmegen,participated in the experiments.3.2 ResultsMean response times and error rates are displayed inTable 2. An analysis of variance on the response times,which crossed the factors Stress (Varied vs. Fixed) andLanguage of the stimuli (Spanish vs. Dutch), revealed asignificant effect of Stress (F(1,48)=11; p<.01) and ofLanguage of the stimuli (F(1,48)=12; p<.01), with nointeraction between them. T-tests restricted to Spanishand Dutch stimuli respectively showed that the effect ofStress was significant for the Dutch stimuli (F(1,24)=10;p<.01) and marginally significant for Spanish stimuli(F(1,24)=3.55; p=.07). A similar ANOVA on error ratesyielded a significant effect due to Language of Stimuli(F(1,48)=4.53; p<.05).Table 2: Mean classification times (in ms) and errorrates of Dutch subjects.Stress patternFixed Varied DifferenceStimuliSpanish 405 / 4.6% 414 / 4.2% 9 / -0.4%Dutch 365 / 3.1% 375 / 3.3% 10 / +0.2%Dutch subjects display interference effects of the samesize whatever the language of the stimuli, though they arefaster and make less errors when the stimuli arepronounced in their maternal language.3.3 Combined AnalysisThe results from the two experiments are displayed inFigure 1. In order to compare them, we combined bothsets of data and performed an ANOVA in which thefactor "Language of the subject" was added. The RTs inthe fixed condition (413 ms) were significantly fasterthan in the varied condition (430 ms; F (1, 104) = 67.24,p < .001). As predicted, this interference effect waslarger for the Spanish subjects (23 ms) than for the Dutchsubjects (9 ms); however, it was only significantly largerfor the Spanish subjects with the Dutch stimuli, andinterference was observed for both subject groups andboth materials sets. There was no statistically significantdifference between response time to tokens with first-versus second-syllable stress. RTs of the Dutch subjectswere significantly faster (390 ms) than those of theSpanish subjects (450 ms); however, this reflected aspeed-accuracy tradeoff, since the error analysis showeda significant difference between subject groups: Spanishsubjects made significantly fewer errors (2.9%) thanDutch subjects (3.8%). No other effect reachedsignificance in the error analysis. Finally, despite the factthat each subject only heard (multiple repetitions of) fourtokens, responses were facilitated when the tokens hadbeen spoken by a native speaker of the subject's language(405 ms in comparison with 435 ms for non-nativetokens).4. CONCLUSIONThese experiments have produced a clear result: listenerscannot ignore stress information while making asegmentally-based classification. This is true both inSpanish, in which stress cannot easily be predicted fromsyllable weight, and in Dutch, in which stress is morepredictable.The findings have potential implications for therelevance of prosodic structure to phonetic processing inspeech recognition. As described in the introduction,previous research suggests that French listeners ignoreaccent information [3], and English listeners do not use360380400420440460480500Const. VariedmsSpanish SsDutch sti.Spanish sti.360380400420440460480500Const. VariedmsDutch SsDutch sti.Spanish sti.123456Const. Varied% errSpanish SsDutch sti.Spanish sti.123456Const. Varied% errDutch SsDutch sti.Spanish sti.Figure 1: Mean classification times and error rates of Spanish and Dutch subjectsstress distinctions in lexical access [1]. The French resultpresumably reflects the irrelevance of accent distinctionsto the determination of word identity in that language.The English result, however, may also reflect language-specific distributional effects. Recent evidence fromperceptual studies in a number of languages suggests thatstress (and indeed other types of prosodic structure) maybe exploited in spoken-word recognition where itsignificantly contributes to reducing the number ofpotential word candidates activated by a given input (see[10] for a review). In English, stress is nearly alwaysunambiguously signaled by segmental structure (vowelquality), so that suprasegmental correlates of stresscontribute little to reduction of the pool of wordcandidates; but in Dutch and in Spanish, thesuprasegmental structure can be more informative.Indeed, Koster and Cutler [11] report that mis-stressingDutch words by varying the suprasegmental pattern alonehas a strong adverse effect on the efficiency with which aword can be recognised, a result which contrasts withearlier reports from English (e.g. [12]).The generality of the interference effect in the presentstudy suggests that the processing of segmentalinformation cannot be performed independently of stress.Nevertheless, the fact that the effect was larger forspeakers of Spanish than for speakers of Dutch suggeststhat the degree of interference from stress variation maybe partially mitigated by the predictability of stressplacement in the language.5. ACKNOWLEDGMENTSThis work was supported by a grant from the SpanishMinistry of Education ("Acciónes Integradas") and partof it was realised when Christophe Pallier was supportedby a post-doctoral grant from the Fyssen Foundation. Wethank Mariëtte Koster and Mark Scholten for technicalassistance.6. REFERENCES[1] A. Cutler, “Forbear is a homophone: lexicalprosody does not constrain lexical access,”Language and Speech, vol. 29, pp. 201-220,1986.[2] W. Jongenburger and V. J. van Heuven, “Therole of linguistic stress in the time course ofword recognition in stress-accent languages,”presented at 4th European Conference onSpeech Communication and Technology, 1995.[3] E. Dupoux, C. Pallier, N. Sebastian, and J.Mehler, “A destressing "deafness" in French?”Journal of Memory and Language, vol. 36, pp.406-421, 1997.[4] W. R. Garner, The Processing of Informationand Structure. Potomac Md: Erlbaum, 1974.[5] C. C. Wood, “Parallel processing of auditoryand phonetic information in speechdiscrimination,” Perception & Psychophysics,vol. 15, pp. 501-508, 1974.[6] L. Lee and H. C. Nusbaum, “Processinginteractions between segmental andsuprasegmental information in native speakersof English and Mandarin Chinese,” Perception& Psychophysic, vol. 53, pp. 157-165, 1993.[7] B. Repp and H.-B. Lin, “Integration of tonalinformation in speech perception: A cross-linguistic study,” Journal of Phonetics, vol. 18,pp. 481-495, 1990.[8] J. L. Miller, “Interactions in processingsegmental and suprasegmental features ofspeech,” Perception & Psychophysics, vol. 24,pp. 175-180, 1978.[9] C. Pallier and E. Dupoux, “EXPE: anexpandable programming language for on-linepsychological experiments,” Behavior ResearchMethods, Instruments, & Computers (in press),1997.[10] A. Cutler, D. Dahan, and W. v. Donselaar,“Prosody in the comprehension of spokenlanguage: A literature review,” Language andSpeech, vol. 40.[11] M. Koster and A. Cutler, “Segmental andsuprasegmental contributions to spoken-wordrecognition in Dutch,” presented at Eurospeech'97: 5th European Conference on SpeechCommunication and Technology, Rhodes,Greece, 1997.[12] L. M. Slowiaczek, “Effects of lexical stress inauditory word recognition,” Language andSpeech, vol. 33, pp. 47-68, 1990.

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Prosodic structure and phonetic processing : A cross-linguistic study

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