Contains report on one research project.U. S. Air Force (Electronics Systems Division) under Contract AF 19(628)-5661National Institutes of Health (Grant 2 ROI NB-04332-06)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E

Klatt, Dennis H.

Menyuk, Paula

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XV. SPEECH COMMUNICATION"Academic and Research StaffProf. K. N. Stevens Prof. D. H. Klatt Dr. Margaret BullowaProf. M. Halle Prof. A. V. Oppenheim Dr. Paula MenyukProf. W. L. Henke Dr. J. S. PerkellGraduate StudentsM. E. Barron A. R. Kent G. L. WickelgrenA. J. Goldberg M. F. Medress J. J. WolfR. M. SachsA. CHILD'S PRODUCTION OF INITIAL CONSONANT CLUSTERS1. ProblemIt has been observed in inventories of the speech sound acquisition of children thatthe articulation of consonant clusters is mastered comparatively late in the sequenceof speech sound mastery. The singleton initial consonants L, R, and S are also lateacquisitions. In normal acquisition, the initial consonants L, R, and S are frequentlyproduced with substitutions and distortions. Consonantal clusters are also producedwith omissions, as well as substitutions and distortions. One might hypothesize thatthis is due to the fact that English initial consonant clusters are composed of C + L, (W)or R, or S + C (C), and each element is subject to systematic production errors. Themanner in which aspects of initial clusters may be stored in the child's lexicon, however,and the changes that occur in the perception and production of these clusters during thedevelopmental period have yet to be described. Indeed, even the facts of production arelargely unknown. No spectrographic, X-ray film, or electromyographic studies ofchildren's articulation of clusters (or other speech sounds) during the period when speechsounds are being mapped into words have been carried out.A recent linguistic discussion proposed that initial clusters may best be describedas single elements in the lexicon. Sequences containing clusters plus a vowel might bedescribed as (C features of L, W or R) (V) rather than (C) ( I ) (V). The sequenceS + L or W are described as strident L and W and the sequence S + C as (S) (C). Seg-mentalization rules spell out the complete set of features for L, W, and R, and thusseparate the elements.3 The features that distinguish a speech sound from a clusterwould be part of the matrix of features for the sound and the cluster in the followingmanner:This work was supported principally by the U. S. Air Force (Electronics SystemsDivision) under Contract AF 19(628)-5661; and in part by the National Institutes of Health(Grant 2 ROI NB-04332-06), the Joint Services Electronics Programs (U. S. Army,U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E).QPR No. 91 205(XV. SPEECH COMMUNICATION)K Kr K1 KwObstruant + + + +Consonantal + + + +Flat - + - +Coronal - + + -There is some historical evidence to support the hypothesis that clusters should beconsidered single elements in the lexicon with some distinctive feature differences indi-cating differences in point and type of release from those of singleton consonants. 4 Ananalysis of the process of acquisition of consonantal clusters may give us further evi-dence of how initial clusters may be stored in the lexicon for productive purposes.2. ProcedureThe utterances of a child, previously recorded at weekly intervals,5 were sampledat 6-month periods from age 18 months to age 30 months, and again at 34 months. Utter-ances containing initial clusters were identified and isolated. At the last age at whichutterances were sampled, initial clusters were still not being accurately produced inthe identified morphemes in the estimation of 4 listeners, and spectrographic analysisindicated that this was indeed the case.During the first observation, the child produced the following utterances containinginitial clusters several times: Brian, truck, plane, and sky. The word Brian was heardas CVC (Bian) and CWVC (Bwian). The word truck was heard as CVC (tuck), CWVC(twuck), and CVC (guck). The word plane was heard only as CVC (bane) and the wordsky only as CV (guy). Throughout the age range alternations of CVC and CWVC wereheard in some instances of C + L or R; however, instances of CVC decreased andinstances of CWVC increased at older age periods. There were instances in which thiswas not the case. The words driveway and truck were heard as 'jiveway' and 'chuck' at30 months. During the first two observations (18 and 24 months), S + C clusters wereheard as d CVC (bank for spank). During later observations, however, the rules thatthe child might be observing to generate these clusters became less obvious. The wordsneaker was heard as 'neager' and the word spoon as 'boon,' but the word swimming washeard as 'shimming' and the word swim as 'sim.' Obviously the C in the C + L or Rclusters and the C in S + C clusters affected production.3. Method of AnalysisIn tracings of the spectrograms obtained from the utterances heard as Bian and guckand Bwian and twuck, it was observed that there seemed to be a more gradual transitioninto the vowel in producing the last two words than in producing the first two, althoughQPR No. 91 206(XV. SPEECH COMMUNICATION)bian guckbwian twuckFig. XV-1. Tracings of spectrograms.a well-formed W was not being produced. This result is indicated in Fig. XV-1.To pursue this finding, utterances that contained initial clusters and singleton initialconsonants that were the same as those in first position in a cluster plus the same vowelwere isolated to see if this distinction could be observed consistently. The utterancesBrian and bike; broke, blow, and boat; and truck and tug were the only ones that couldbe found in the language samples examined. Tracings of spectrograms obtained fromthese utterances indicated that in the case of clusters there was a more gradual transi-tion into the vowel than in the case of singleton consonants. These tracings are shownin Fig. XV-2. The age at which the utterance was produced is in parentheses.Spectrograms of children's utterances, however, are often far from clear. A broad-band spectrogram of a child's utterance, intended to be the word "Brian," appears inFig. XV-3. The child has a fundamental frequency of the order of 300 Hz. Thereforethe broadband spectrographic display is resolving individual harmonics of the glottalsource. The formant frequencies, and thereby the articulatory pattern, must be esti-mated from the changing pattern of harmonic levels seen in the figure.A spectrogram of the same word as spoken by an adult male is shown in Fig. XV-4.In this case the formant frequencies are clearly defined. The consonant cluster [br] ismanifested as a rapid rise in all formant frequencies immediately following the release(characteristic of a labial stop), and this gesture is followed by a period of time duringQPR No. 91 207L ________________________ Lbroke (30 mos.) Brian (18 mos.) truck (18 mos.)I _______________________________ Iblow (34 mos.) bike (18 mos.) tug (34 mos.)boat (18 mos.)Fig. XV-2. Tracings of spectrograms.i~-----....................... ..........~---Fig. XV-3. Spectrogram of the word "Brian", spokenat age 18 months.Fig. XV-4. Spectrogram of the word "Brian" spoken by an adult male.QPR No. 91____ _ ~CqL=_209(XV. SPEECH COMMUNICATION)which the third formant is very low and close to the second formant (characteristic ofa retroflex articulation). The formants then move continuously through trajectoriesof the diphthong [aI].The extent to which the child's production is an adequate replication of an adult pro-duction is not obvious. Fortunately, the data from the child includes a contrasting utter-ance, "bike." A spectrogram of this word appears in Fig. XV-5.Fig. XV-5. Spectrogram of the word "bike" spoken at age 18 months.Figures XV-3 and XV-5 do not permit a sufficiently accurate estimation of formantfrequency locations to make a definite comparison. Therefore, a computer-controlledfilter-bank spectral analyzer was used to supplement the analysis. Figure XV-6 con-tains one frame from a computer-controlled "spectral movie" of the words "Brian" and"bike" as spoken by the child. 7 The spectral frame corresponds to a time approximately50 msec after the release of the initial stop in each word.The third formant is clearly visible and the positions of the first and secondformants can be estimated from the relative amplitudes of the harmonics of thefundamental frequency. By watching a slow-motion replay of the spectral movie, itis possible to get an even better feeling of formant locations by the way in which har-monic amplitudes change as a function of time. The natural ability of the eye toestimate a spectral envelope from this moving pattern is thwarted on the spectrogramsQPR No. 91 210(XV. SPEECH COMMUNICATION)"BRIAN"FIRST FORMANT FREQUENCY = 650 HzSECOND FORMANT FREQUENCY = 1750 HzTHIRD FORMANT FREQUENCY = 4050 Hzo ooooI I I I I I I0 5 10 15 20FILTER NUMBER25 30 35"BIKE"FIRST FORMANT FREQUENCY = 850 HzSECOND FORMANT FREQUENCY = 1850 HzTHIRD FORMANT FREQUENCY = 4000 Hzo oo o0 0o0o ooooI~ ~ 0 00 5 10 15 20FILTER NUMBERFig. XV-6. Outputs from a filter bank 50 msec afterthe release of the initial stop in the words"Brian" and "bike" spoken by the child.because of the poor amplitude resolution.The words "Brian" and "bike" have been compared with the aid of the computer dis-play. The results indicate that "Brian" does not have the required lowered third for-mant following release, but that there are some differences in the initial portions of thetwo words. If we assume that the peak in the first formant trajectory indicates theclosest approach to the [a] articulation, it then follows that the word "Brian" takeslonger to reach the [a], and that the first two formant frequencies are lower throughoutthe utterance than for the word "bike."From these observations it might be concluded that an adult listener will not hear an[r] when presented with the word intended to be "Brian," but that he is likely to believethat some kind of phonetic segment is interposed between the [b] and the [al]. This seg-ment is acoustically most similar to a [w].8In summary, then, "Brian" does not contain an acceptable [r], but does show someindication of an initial consonant cluster. The cluster is acoustically most similar to[bw].4. Tentative ConclusionsSeveral hypotheses about the production and possible perception of clusters might bederived from the observation of the 4 listeners and the results of the analysis. The firstQPR No. 9125 30 35ooo0 0a000 00 000 oo211(XV. SPEECH COMMUNICATION)is that CCV syllables are initially always produced as CV, and that the child has yet toobserve any distinctions between morphemes composed of CV and CCV sequences. Inthat case, it would seem reasonable to suppose that either the first segment or the sec-ond segment of the cluster would be consistently omitted. In fact, it is always the Land R, the second segments in clusters, or the S, the first segment in clusters, whichare consistently omitted. Another hypothesis, then, might be that the child has observeddistinctions between CV and CCV syllables, but has yet to produce these distinctions,since it is always the predictable segment of these clusters which is omitted (that is,+consonantal +consonantalC + +consonant is always C + L, or R; C + +consonant is always S + stop or nasal).-obstruant ±obstruantThis in turn leads to the hypothesis that the child has acquired some of the morphemestructure rules of his language, and observed some segmental features so that theserules can be applied.According to the analysis of the data, as well as observer estimation, the followingfactors may be occurring in the process of mastering the articulation of initial clusters.C + L, W, R, are produced initially with only the C of the cluster (bane for plane, Bian-obstruantfor Brian, guck for truck). Later, they are produced as C + (+gradual release ) with+gradual releasethe release possibly being homorganic (in the same place of articulation as C). ThusBwian and bwoke are produced, but chuck and jiveway are also produced. (This obviouslydoes not account for the twuck that was heard.) Clusters with S + C are produced as+ C in the case of stops and nasals (guy for sky and neager for sneaker), but as+strident + 5 in the case of W and L (shimming for swimming and sim for swim).Other factors may be operating as well. The voicing of stops in clusters (guck, bane,and guy) indicates, perhaps, that the child has observed the lack of aspirationin clusters.From these results, one might hypothesize that children have very complicated rulesfor the production of clusters. On the other hand, one might hypothesize that clustersare indeed entered in the child's dictionary as single segments rather than as a sequenceof segments for productive purposes. At age 34 months the rules for filling in the com-plete set of features (segmentalization rules) and for separating these elements for pro-ductive purposes have not yet been acquired. Thus, C + L, W, R may be initiallyentered as ( gradual homorganic release) and additional features then added to the con-+stridentsonant (±flat, ±coronal). S + W or L may be entered as ( C+strident ), and then additional+obstruantfeatures added to C (±coronal, ±anterior) and S + nasal or stop as (C ), andadditional features added to +obstruant (+strident, +coronal, +anterior).As we have stated, the data are quite sparse and, therefore, a far from full accountis possible. The validity of some of these assumptions will be tested in an experimentin which children are asked to identify morphemes with initial consonant clustersor singleton consonants. The various feature contrasts such as place (pr, tr,kr, etc.), voicing (pr, br, etc.) and cluster composition will be examined. TheQPR No. 91 212(XV. SPEECH COMMUNICATION)children will also be asked to reproduce sentences containing the same morphemes.The morphemes produced will then be analyzed according to the method discussed.Paula Menyuk, D. H. KlattReferences1. D. McCarthy, "Research in Language Development: Retrospect and Prospect,"Monogr. Society for Research in Child Development 24, 3-24 (1959).2. M. H. Powers, "Functional Disorders of Articulation - Symptomatology andEtiology," in L. E. Travis (ed.), Handbook of Speech Pathology (Appleton-Century-Crofts, New York, 1957).3. T. R. Hoffman, "Initial Clusters in English," Quarterly Progress Report No. 84,Research Laboratory of Electronics, M. I. T. , January 15, 1967, pp. 263-274.4. T. B. Gamkrelidge, "A Typology of Common Kartvelian," Language 42, 69-83 (1966).5. M. Bullova, L. Jones, and T. Bever, "The Development from Vocal to VerbalBehavior in Children," Monogr. Society for Research in Child Development 29,101-107 (1964).6. N. Benheim, "Real-Time Spectral Input System for Computer Analysis of Speech,"Quarterly Progress Report No. 80, Research Laboratory of Electronics, M. I. T.,January 15, 1966, p. 197.7. The computer program was developed by J. J. Wolf of the Speech CommunicationGroup of the Research Laboratory of Electronics.8. An alternative [f], can be ruled out, because of the absence of a stoplike discontinuousincrease in the first-formant frequency typical of the release of an [f] into the [al].QPR No. 91 213

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