Contains research objectives and reports on three research projects.U. S. Air Force (Electronic Systems Division) under Contract AF19(628)-5661National Institutes of Health (Grant 5 RO1 NB-04332-04

Benhaim, N.

Halle, Morris

Klatt, Dennis H.

Menyuk, Paula

River, Eleanor C.

Stevens, Kenneth N.

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XXVIII. SPEECH COMMUNICATIONAcademic and Research StaffProf. K. N. Stevens Prof. A. V. Oppenheim C. -W. KimProf. M. Halle Dr. Margaret Bullowa N. BenhaimProf. W. L. Henke Dr. Paula Menyuk J. S. PerkellProf. D. H. Klatt Dr. J. Suzukit Eleanor C. RiverK. FintofttGraduate StudentsJ. K. Frediani L. R. Rabiner M. Y. WeidnerA. J. Goldberg R. S. Tomlinson J. J. WolfRESEARCH OBJECTIVESThe objective of the research in speech communication is to gain an understandingof the processes whereby (a) discrete linguistic entities are encoded into speech byhuman talkers, and (b) speech signals are decoded into meaningful linguistic units byhuman listeners. Our general approach is to formulate theories or hypotheses regardingcertain aspects of the speech processes, obtain experimental data to verify these hypoth-eses, and simulate models of the processes and compare the performances of themodels and of human talkers or listeners. Research in progress or recently completedincludes: observations of the acoustic and articulatory aspects of speech production inEnglish and in other languages through spectrographic analysis; study of cineradio-graphic data and measurement of air-flow events; study of the perception of speechsounds by children and examination of the acoustic properties of the utterances of chil-dren; computer simulation of articulatory movements in speech; investigation of themechanism of larynx operation through computer modeling and acoustic analysis; exam-ination of new procedures for analysis of speech signals using deconvolution techniques;experimental studies of the perception of vowel sounds; speech synthesis by rule with acomputer-simulated terminal analog synthesizer; a re-examination of the system of fea-tures used to describe the phonetic segments of language; and the development andimprovement of interface equipment for spectral analysis of speech with a computer andfor synthesis of speech from computer-generated control signals.K. N. Stevens, M. HalleA. REAL-TIME SPECTRAL INPUT SYSTEM FOR COMPUTERANALYSIS OF SPEECHOn-line operation of a real-time spectral input system for computer analysis ofspeech was achieved during the period covered by this report. The system, mentionedin a previous report,l was used with a bank of 36 bandpass filters and a PDP-1 com-puter to analyze recorded utterances played back in real time. A block diagram of thecomplete analyzing configuration is shown in Fig. XXVIII-1.This work was supported principally by the U. S. Air Force (Electronic SystemsDivision) under Contract AF19(628)-5661; and in part by the National Institutes ofHealth (Grant 5 RO1 NB-04332-04).fOn leave from Radio Research Laboratories, Tokyo, Japan.1On leave from Norges Laererhogskole, Trondheim, Norway.QPR No. 84 253(XXVIII. SPEECH COMMUNICATION)Operation of the system is, at present, completely under program control. Whenin data-taking mode, the program continually pulses the real-time analyzer, therebycausing it to read and convert the output of each channel. Channel stepping is performed--------------------------- -- ------ 1223 LINEARFULL-WAVE ,AUDIO IN FILTER RECTIFIERS MPX LOGARITHMIC 6-BIT DATA" SET I + SWITCHES A TO D PDP-LOWPASS 0 - 63 dbFILTERS I36,' SAMPLING PULSESREAL -TIME ANALYZERL ----------- -- -___ - -Fig. XXVIII-1. Diagram of the real-time analyz er as used withanalyzing filter bank and PDP-1 computer.at the end of each conversion by the internal logic of the analyzer. Digitized channelinformation is sent back to the computer and stored in the core. When the sum of theoutputs of three selected channels rises above a set threshold, the program recognizesthe onset of speech. Termination of speech is similarly recognized. The beginning andend thresholds and the sampling rate are program parameters. At present, 4000 wordsof data may be stored, representing approximately 3.4 seconds of speech at a 10-msecsampling rate. The program can display any given 36-channel spectrum sample andalso each spectrum sample in sequence throughout the utterance. A display of selectedchannels outputs as a function of time is also available.N. Benhaim, Eleanor C. RiverReferences1. N. Benhaim, "Real-Time Spectral Input System," Quarterly Progress Report No. 80,Research Laboratory of Electronics, M. I. T., January 15, 1966, p. 197.B. CHILDREN'S PERCEPTION OF A SET OF VOWELSIn experiments comparing identification and discrimination functions for vowels inisolation and in consonantal context, it has recently been found that vowels in contexttend to be perceived in a categorial fashion. Discrimination functions are characterizedby peaks at the phoneme boundaries, whereas isolated vowels form a perceptual con-tinuum. It is felt that these results support the theory that experience with theQPR No. 84 254(XXVIII. SPEECH COMMUNICATION)generation of speech movements and with simultaneous observation of the acoustic con-sequences of these movements plays an important role in shaping the process wherebyspeech is perceived. 1In the case of a child the acoustic consequences of his speech movements differquite radically from the consequences produced by the adults in his environment. Thequestion asked in this experiment was: Are the phoneme boundaries for a set of vowelsin consonantal context the same for the child as for the adult. Six children and 5 adultsconstituted the population of this study. The children, three boys and three girls,ranged in age from 5 to 11 years.Each subject listened through earphones to 90 stimuli consisting of random presenta-tion of 9 different synthetically produced CVC syllables. Two of the 9 syllables (steps2 and 8) formed a typical version of b/iL/ and b/I/1 spoken by an American male. Fiveadditional stimuli were produced by computing a set of interpolated formant contoursthat were equally spaced between b/i/1 and b/I/1 (steps 3-7). Two more were producedby extrapolating one step before b/i/1 and one step after b/I/1 (steps 1 and 9). Thesestep sizes were equal to those between the interpolated stimuli. This produced 9 differ-ent syllables. (For a more detailed discussion of the stimuli see Stevens.l)Three black and white drawings pasted to a black surface were placed before eachsubject and identified by the experimenter as b/i/1 (a truck), b/I/1 (a bird's bill) andb/&/1 (a church bell). The subjects were asked to point to the picture that the speakerwas naming. The percentage of judgments for each subject as /i /, /I/ or /,/ for eachof the 9 steps was then computed and a mean for adults and children was obtained.Table XXVIII-1 gives the numerical results.Table XXVIII-1. Per cent of judgments /i/, /I/, /6/ as a function of step.ADULTS CHILDREN ADULTS CHILDREN ADULTS CHILDRENStep % . % % % % , %p>. 0 5 .QPR No. 84 255(XXVIII. SPEECH COMMUNICATION)There were no significant differences between adults' and children's judgments oneach step except for step 3 as computed by chi-square comparison. The tendency isfor the adults to begin to perceive /I/ "sooner" in the continuum than the children, andfor the children to do so with /</, although not significantly so. Figure XXVIII-2 showsthat phoneme boundaries for the vowels in this experiment are the same, in terms ofsteps, for the children and for adults.s CHILDREN100 - q I e-4 ADULTS/80 -a0_60-40 -Z0-- I200 2 4 6 8STIMULUS STEPFig. XXVIII-2. Phoneme boundaries for vowels in the experiment.The answer to the question that was raised, therefore, is yes for the set of vowelsin this experiment. This leaves us, however, with the task of trying to explain how thechild can identify vowels in much the same way as adults when he produces these vowelsso that they are, in terms of formant frequency, a poor match with those of the adults.We might also ask how the adult identifies the vowels produced by children.There are several possibilities concerning the perceptual cues that may be in opera-tion. Although the child's vowels do not match the adult's, his set of vowels are clearlydifferentiated from each other in formant frequencies. Furthermore, the direction thatdifferences take for F I and F2 between vowels is the same for adults and children. Also,there is no overlap between the vowels produced by children and adults. That is, forexample, the /I/ produced by the child is not like the /L/ produced by the adult in termsof formant frequencies. Therefore, a system of distinctive differences exists betweenthe vowels produced by children, as well as between the vowels of children and adults.(The data will be reported in detail elsewhere.2) Two further speculations would bethat acoustic characteristics other than formant frequencies provide cues for identifica-tion and that articulatory gestures used by children to produce the vowels might be anal-ogous to those used by adults. The first speculation is now being examined from dataobtained in a previous experiment.3 We have, at this time, no data on the articulatorygestures of children. We have the task of identifying those parameters by which theQPR No. 84 256(XXVIII. SPEECH COMMUNICATION)child matches what he produces to what the adult produces and those by which the adultmatches what he produces to what the child produces so that there is mutual under-standing, which does, in fact, exist.We have found that the child identifies certain vowels in consonantal context categor-ially, as does the adult, and that the boundaries of these vowels are strikingly similarfor both children and adults. We would like to explore this question with other speechsounds; primarily, with those sounds that create difficulty developmentally, such asw, r, 1, y.Paula MenyukReferences1. K. N. Stevens, "On the Relations between Speech Movements and Speech Percep-tion, a paper presented at the 18th International Congress of Psychology, Moscow,August 1966.2. Paula Menyuk, "Children's Production and Perception of a Set of Vowels" (inpreparation).3. Paula Menyuk, "Cues Used in the Perception and Production of Speech by Children,"Quarterly Progress Report No. 77, Research Laboratory of Electronics, M. I. T.,April 15, 1965, pp. 310-313.C. ARTICULATORY ACTIVITY AND AIR FLOW DURING THE PRODUCTIONOF FRICATIVE CONSONANTSOne of the principal objectives of research in speech is to understand the mechanismunderlying the control of the speech-generating system. Several kinds of experimentalobservations can be made in order to investigate the nature of this process. Amongthese, air-flow and pressure measurements can provide useful information concerningthe activities of the various articulatory structures. The purpose of this report is. todescribe one result of a larger study that has been reported on elsewhere. 1 Measure-ments of air flow during speech production have led to certain conclusions about themanner in which voiceless fricatives are produced in intervocalic position.A face mask incorporating a linear flow resistance and a pressure transducer wasused to measure the volume velocity of the air stream expelled from the lungs duringspeech production. 1 - 3 Figure XXVIII-3 is an example of the graphic record for theutterance "Say the word /he'fdf/ again." A double peak in the air flow occurs for each/f/ phone as indicated by the arrows. This type of double peak is characteristic of thevoiceless fricatives /f, 0, s, S/ in the context of this frame sentence for all 5 speakersstudied.The double peak is probably a consequence of the relative timing of laryngeal andarticulatory gestures. In Fig. XXVIII-4 a tracing of average air flow is compared withQPR No. 84 257(XXVIII. SPEECH COMMUNICATION)Air flowfrom mask(liters/sec)6 I 2 secSay theword /ha f a f/ againFig. XXVIII-3. Example of the air-flow record (inverted) fromthe graphic recorder for the utterance "Say theword /h 'fof/ again." (Speaker: KNS.)1.0 IpsFig. XXVIII-4. Spectrogram and tracing of average air flowutterance "Say the word /h e'fof/ again."The lines indicate the times of cessation andinitiation of voicing in the syllable /fof/.a spectrogram of the utterance to indicate the times of voicing onset and cessation. Thelines that mark these times occur approximately at air-flow peaks.An interpretation of these results in articulatory terms is suggested in Fig. XXVIII-5.During the unstressed vowel/a/, the glottis begins to open while the vocal cords con-tinue to vibrate. At the first peak in air flow (indicated by the first dashed line) thelower teeth begin to make contact with the upper lip, and the constriction that is formedcauses a rise in mouth pressure. As a result, vocal-cord vibration ceases ratherabruptly. The supraglottal articulator continues to constrict until vocal-tract resistancereaches a maximum value. The articulator then begins to move away in anticipation ofthe next phone, thereby lowering vocal-tract resistance. Air flow through the glottisthus increases, the vocal cords approximate as a consequence of the reduced pressure,and vocal-cord vibration begins (at the point indicated by the second dashed line).Finally, the vocal cords assume a mode of vibration which is characteristic of thevowel, with higher glottal resistance. A similar pattern of the air flow occurs in theQPR No. 84 258(XXVIII. SPEECH COMMUNICATION)GLOTTALRESISTANCERGTIMEVOCAL TRACTRESISTANCERvTTIME( RG +RVTa f a TIMEFig. XXVIII-5. Interpretation of the articulatory eventscausing a double peak in the air-flowtrace for a voiceless fricative in inter-vocalic position. Total resistance toflow is assumed to be the sum of glottalresistance and vocal-tract resistance.Dashed lines indicate times of cessationand initiation of voicing.final /f/ of the utterance illustrated in Fig. XXVIII-4.The voiced fricatives, /v z v/ display similar air-flow traces, except that air flowis reduced relative to that of the voiceless fricatives, and the double peak is less pro-nounced. Voicing occurs throughout these sounds, but the flow becomes higher than fora vowel in spite of the turbulence-producing supraglottal constriction. Thus the laryn-geal mode of vibration for voiced fricatives must differ from that occurring duringvowels; the vocal cords probably remain separated during a vibratory cycle, with theresult that there is an appreciable DC component to the flow.In the course of the study,1 data were gathered on other consonants of English.Some consonant clusters were recorded and found to have air-flow traces exhibitingcoarticulation effects. Word stress was found to have some effect on air flow. Thedata suggest certain limits on the speed of reaction and coordination of larynx andvocal-tract structures during speech production.The experimental data reported here were obtained at the Harvard School ofPublic Health, in collaboration with Dr. Jere Mead of its Department of Phys-iology.D. H. KlattReferences1. D. H. Klatt, K. N. Stevens, and J. Mead, "Studies of Articulatory Activity and AirFlow during Speech," Proc. Conference on Sound Production in Man, New YorkAcademy of Sciences, 1966 (in press).QPR No. 84 259(XXVIII. SPEECH COMMUNICATION)2. J. F. Lubker and K. L. Moll, "Simultaneous Oral-Nasal Air Flow Measurementsand Cinefluorographic Observations during Speech Production," The Cleft PalateJournal, Vol. 2, pp. 257-273, July 1965.3. N. Isshiki and R. Ringel, "Air Flow during the Production of Selected Consonants,"J. Speech Hearing Res. 7, 233 (1964).QPR No. 84 260

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