Quarterly Progress and Status Report. Fundamental frequency patterns and the long-short vowel distinction in Swedish

Transcription

1 Dept. for Speech, Music and Hearing Quarterly Progress and Status Report Fundamental frequency patterns and the longshort vowel distinction in Swedish Rosen, S. M. journal: STLQPSR volume: 18 number: 1 year: 1977 pages:

2

3 STLQPSR 1/ C. FUNDAMENTAL FREQUENCY PATTERNS AND THE LONGSHORT VOWEL DISTINCTION IN SWEDISH Stuart M. ~osen* Abstract The effect of various fundamental frequency contours on the longshort categorization of a vowel was studied in 10 Swedish subjects. The long short pair used was ett ( / E t/, "one") Xt (/E :t/, "eat! If). These two words can be differentiated solely on the basis of duration of the vowel. Six durations of the vowel were possible: 50, 75,, 125, 150 and 175 msec. Five different fundamental frequency patterns were possible: rising from Hz at. 5 ~z/msec, falling from 200 Hz at. 5 ~z/msec, level at 150 Hz, level at 200 Hz and level at Hz. This made for a total of 30 possible stimuli which were presented to the subjects in a random order who rated them as being more like "ettm Or I I ~ ~. I I The categorization functions for each of the different pitch patterns were essentially indistinguishabl'e. The values of the phoneme boundary differed at most by 6 msec. Thus, fundamental frequency contours are in fact irrelevant in this long short distinction. This finding is discussed in relation to reports that vowels with a changing fundamental have a greater perceived duration than vowels with a level fundamental. Introduction Several reports have recently appeared which suggest that the per ceived duration of a speech segment can be affected through its funda mental frequency contour (Lehiste; 1976, Wang, Lehiste, Chang and Darnovsky; 1976, Pisoni; 1976). The consensus of these papers is that stimuli with a rising fundamental are perceived as being longer than stimuli with a falling fundamental which in turn are perceived as being longer than stimuli with a level fundamental, when all stimuli are physically equal in duration. Although reservations about these data have been expressed (~osen; 1976, 1977) the implications of such an effect on the under stakding of speech rhythm and timing demand its thorough investigation. As suming for the moment that fundamental frequency contour s do affect perceived duration in the described manner, where would these effects be likely to manifest themselves in a more "speechlike" situa tion? An obvious example (as well as convenient from an experimental point of view) is the longsliort vowel distinction in Swedish, which can in certain cases, be signalled solely by duration of the vowel. Although * Guest researcher at the Dept. of Speech Communication from MIT, Cambridge, Mass., June 30, 1976 May 15, \

4 STLQPSR 1/ the duration of the following consonant usually varies inversely with the duration of the vowel (especially in stressed syllables), it seems that the consonant duration actually plays a very small role. That the distinc tion can be made solely on the basis of duration of the vowel has been shown by HaddingKoch and Abramson ( 19 64) and Jonas son and McAlli ster (1972). An attempt is made here to predict shifts in the phoneme bound ary between long short vowels that would be expected from fundamental frequency contours of the type used in Rosen (1977). The long short pair chosen was ett (/E t/, "one") 3t (/E :t/, "eat! It). As previous, a level 150 Hz vowel serges as the reference on which to judge other conditions. The other fundamental frequency conditions were also chosen to correspond to those used in Rosen (1977): falling, rising, level at 200 Hz and level at Hz. The points of subjective equality (PsE' s) found in Rosen (1977) should be able to predict at least the directian of change in the phoneme bounda ries due to the presence of various fundamentals. In particular, if a rising or falling fundamental lead to increased perceptual duration, we would expect the value of the phoneme boundary to decrease. As a level 200 Hz stimulus also gave a larger PSE, we would expect the boundary here to decrease also. However, as the level Hz stimulus had a smaller PSE, we would expect its boundary to increase relative to the level 150 Hz. Materials and methods The stimulus set consisted of various versions of the segment /~t/. Six durations of the vowel were possible: 50, 75,, 125, 150 and 175 msec. Five different fundamental frequency contours were used for each duration of the vowel: rising from Hz at a rate of. 5 ~z/msec, fal ling from 200 Hz at a rate of. 5 ~z/msec, level at 150 Hz, level at 200 Hz, and level at Hz. This made for a total of thirty stimuli. The formants of the vowel, as well as all the characteristics of the consonant were kept constant over all the stimuli. The consonant had a duration of approximately 200 msec and was aspirated. Stimuli were presented in a oneinterval two alternative forced choice paradigm. Each trial consisted of a presentation of one of the 30 stimuli, and subjects were asked to choose, by checking the appropriate column

5 STLQPSR 1/ on an anwer sheet, whether the segment sounded more like ett (/et/,. llone") or St (/E :t/, "eat!"). The stimuli were generated by the OVE I11 formant synthesizer under the control of a synthesis byrule program (Carlson and Granstriim; 1976) running on a CDC 1704 computer. Th6 stimulus tapes were re corded from OVE, and consisted of trials. There were three pre sentations of each of the thirty stimuli per session making for a total of 90 stimuli. These stimuli were randomized subject to the condition that all stimuli were presented before any were repeated. Nine stimuli were added to the beginning of the session for practice, and one to the end, bringing the total to. Two different experimental tapes were made. Ten subjects, all native Swedish speakers drawn from the staff of the Department of Speech Communication at the Royal Institute of Tech nology, participated in the experiment, Seven of these subjects parti cipated in the main experiment of Rosen (1977). Each subject judged both tapes, with at least 24 hours between sessions in a counterbalanced order. Thus, each subject gave six responses to each stimulus, giving a total, over all subjects of 60 responses to each stimulus. Subjects listened to the stimuli through headphones in a quiet room. Each session lasted about ten minutes. Results and discussion The probability of a short vowel response, averaged over all subjects, is shown for each of the 30 stimuli in Table IC I. are plotted, for each type of pitch contour, in Fig. IC I. These probabilities Clearly, the categorization functions are quite alike for all fundamental frequency con tours. The irrelevance of the contours in determining the longshort response can also be seen in the proportion of short vowel responses for each type of contour averaged over all durations, also shown in :Table ICI. These proportions all lie between and /0 and are not significantly different from one another. As a more quantitative measure, the probabilities of Table ICI not equal to zero or one were converted to normal deviates and subject to a Miiller Urban least squares fitting process (Guilford; 1954). The pho neme boundaries (50 70 probability of a short Qowel response) and the 75 % difference limens (the number of msec needed to go from 50 OJa short

6 r STIMULUS DURATION (msec) STIMULUS TYPE SO 17 5 AVG ALL DUR RISING. 5 ~ z/msec FALLING. 5 ~ z/msec. 83.3, I LEVEL 150 Hz LEVEL 200 Hz LEVEL Hz : 1 TABLE ICI. The probability of a short vowel response as a function of duration and fundamental frequency pattern.

7 I 1 I I I I Level 150 Hz Level 200 Hz.... Level I00 Hz.. Rising.. Falling I VOWEL DURATION (rnsec) Fig. IC I. The probability of a short vowel response as a function of duration for five fundamental frequency patterns.

8 STLQPSR 1/ vowel responses to short vowel responses) derived from these best fitting lines are shown in Table IC11. The values for the phoneme boundary never differ by more than 6 msec from each other, and more importantly, do not shift in a regular manner. The phoneme boundary for the rising stimuli which was pre dicted to be lower than that for the level 150 Hz stimuli, is higher. The two stimuli which seemed to have the most different perceived durations in the previous study (~osen; 1977), the and 200 Hz level stimuli, have almost preciselythe same phoneme boundaries, and averaged over all durations, lead to exactly the same number of short vowel responses. Conclusions If the pitch contour on a yowel affects that vowel' s perceived duration as asserted by Lehiste (1976), Wang, et. al. (1976) and Pisoni (1976), phoneme boundaries in the long short vowel continuum used hef e should have been affected by the pitch contour on the vowel. That they were very clearly not affected, and there is no doubt about this, suggests a number of possibilities. One approach is to assert that pitch patterns do affect perceived dura tion, but that they also affect the placing of phoneme boundaries in a precisely complementary manner. A second approach is to invoke the "speech mode'l explanation, which is to say, speech perception may not necessarily follow the rules deter mined in a non speech judgement task. Finally, one may use this data to invoke further uncertainty about the role played by fundamental frequency contours in determining perceived duration. Enough oddities in the psychophysical data exist, as has been argued by Rosen (1977), to make this a not unreasonable position. In any case, both from the results reported previously (~osen; 1977) and in this study, it seems unlikely that the effect of fundamkntal frequen cy contours on perceived duration will be found to be particularly im portant in speech, especially compared to the effects of the fundamental frequency contour s themselves...

9 r STIMULUS TYPE PHONEME BOUNDARY (msec) 75 % D~(msec) RISING.5 ~z/msec FALLING.5 ~z/msec LEVEL 150 Hz LEVEL 200 HZ LEVEL Hz TABLE IC11. Phoneme boundaries and difference lirnens as a function of fundamental frequency pattern.

10 STLOPSR 1/1977 Acknowledgments Enough thanks cannot be expressed to Rolf Carlson and Bjtirn Gran striim who, among other things, adapted their synthesis programs for use in this experiment. I must also thank my subjects, who know that running in such experiments is not often fun. The author was supported by a National Science Foundation Graduate Fellowship. References CARLSON, R. and GRANSTR~M, B. (1976): "A textto speech system based entirely on rules", ~onf.~ecord 1976 IEEE Int. ~onf. on Acoustics, Speech arid =pal Processing, Philadelphia, Pa., USA, pp GUILFORD, J.P. (1954): Psychometric Methods, McGrawHill Book Co., 2nd edition, pp HADDING KOCH, K. and ABRAMSON, A. S. (19 64) : "Duration versus spectrum in Swedish vowels: Some perceptual experiments", Studia Linguistica 18, pp JONASSON, J. and McALLISTER, R. H. (1972): "Foreign accent and timing: An instrumental phonetic studyi1,,in Papers from the Institute 14, pp of Linguistics University of Stockholm LEHISTE, I. (1976): "Influence of fundamental frequency pattern on the perception of durationft, 3. of Phonetics 4, pp PISONI, D. (1976): "Fundamental frequency and perceived vowel durations", paper presented at the 9 I st meeting of the Acoustical Society of America, Washington, D. C. ROSEN, S. M. (1976): "Linear FM pitch sweeps and perceptual duration in speech and nonspeech", STLQPSR 4/1976, pp ROSEN, S. M. ( 1977) : "The effect of fundamental frequency patterns on perceived duration", STLQPSR 1/1977, pp WANG, W.SY., LEHISTE, I., CHANG, CK. and DARNOVSKY, M. (1976): ttperception of vowel durationt1, paper presented at the 92nd meeting of the Acoustical Society of America, San Diego. I