Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

Temporal organization ofsyllable production

Lindblom, B.

journal: STL-QPSRvolume: 9number: 2-3year: 1968pages: 001-005

http://www.speech.kth.se/qpsr

msec

EFFECT OF WORD LENGTH

ON SEGMENT DURATION IN { SEQUENCES

I I I I I

INITIAL CONSONANT -

- -

- -

-%- I I I I I

msec

400

. I I I I I

VOWEL - - long

o short -

Ca :I

I I I I I

1 2 3 4 5 1 2 3 4 5

NUMBER OF SYLLABLES PER WORD

Fig. I-A-1. Consonant and vowel segment durations as a function of the number of syllables per test word. The measure- ments refer to word initial syllables with main stress .

EFFECT OF STRESS

msec

ON SEGMENT DURATION IN C C V I SEQUENCES

I I I I I

INITIAL CONSONANT - c bl s t ressed

o unstressed

- -

-A- I I I 1 I

msec

300

1 2 3 4 5 1 2 3 4 5

NUMBER O F SYLLABLES PER WORD

I I 1 I I

VOWEL - - s t ressed

C a1 o unstressed

1\11 - I I I I 1 .

Fig. I-A-2. Compar ison between the data shown i n Fig. I-A-1 on the dura t ion of s t r e s s e d consonant and vowel segments and measu remen t s of the corresponding segment du ra - t ions in uns t ressed position. The open c i r c l e s per ta in to word initial syl lables with weak s t r e s s .

d

vowels vary a s a function of word length, The data pertain to word ini-

t ia l syllables with main s t r e s s and have been taken f rom a single female

talker. The effects shown a r e found for a l l other subjects a s well. The

graphs indicate that a s the number of syllables pe r word increases con-

sonant and vowel segments decrease in duration. The long vowel is

indicated by solid c i rc les and the short vowel by open c i rc les . It i s ap-

parent that they behave s imilar ly with respect to word length.

The Effect of S t r e s s

In Fig. I-A-2 we present a comparison between the data just shown

on the duration of s t r e s sed consonant and vowel segments and rileasure-

ments of the corresponding segment durations in unstressed position.

The open c i rc les pertain to word initial syllables with weak s t r e s s . On-

ly two degrees of s t r e s s will be distinguished: strong and weak s tress .*

The data points indicating unstressed values re fer to a pooled average of

a l l the unstressed data i n word initial position. F r o m an examination of

this figure and the corresponding ones for other ta lkers i t i s c l ea r that

the duration of unstressed segments i s approximately constant and in-

dependent of word length whereas the s t r e s sed data exhibit longer values.

The Effect of Position

Fig. I-A-3 indicates the generally observed effect that position with-

in the word has on segment duration. The preceding figures have pre-

sented data f rom word initial positions. The plots i n this figure include

in addition information on durations in medial and final positions. As

before segment durations a r e plotted against the number of syllables

p e r word. In this case the durations of unstressed [ a ] and s t r e s sed

[ a : ] a r e shown to the left and right, respectively. F o r each given

word length the data on initial, medial, and final positions i s arranged

sequentially along the x-axis. It should be pointed out that word

f i ~ a l position i s a lso phrase final fo r the data shown. Straight -- - - .- - - - - - - - -- -

* Meaningful Swedish words whose s t r e s s contours and accent patterns conform with those s e l e ~ t e d for the present nonsense vocabulary have been described (J) a s having three degrees of

4 0 1 0 1 0 4 0 1 0 4 s t r e s s , e. g. bockerna, muhammedan, egyptolog~ etc. where ( 5 ) 4 represents main s t r e s s and 1 and 0 two degrees of weak s t r e s s .

The model words used in the present investigation s e e m auditor- i ly to have been pronounced with no distinction between degree 1 and 0, and there i s no c l ea r durations1 basis for i t in the data examined s o f a r . In most cases , however, the perceptual reali ty of these levels i s an unquestionable fact.

STL-QPSR 2-3/1968 3.

l ines connect the points for a given word length. In the c a s e of both

the unstressed [ a ] and the s t r e s sed [ a : ] it is evident that the shortest

durations a r e observed for the word initial positions. The medial

data points tend to c lus te r c loser to those indicating word initial dura-

tions. In no case is i t possible to demonstrate for any subject that

the final segment durations a r e shor t e r o r equal to the initial segment

durations fo r any given word length. Final lengthening is a feature of

both unstressed and s t r e s sed syllable segments but i s m o r e marked

f o r the vowels and syllable final consonants. As 3 rule, the unstressed

segments exhibit l i t t le dependence on the number of syllables p e r word.

Such a dependence, however, i s c lear ly apparent i n the right-hand

plot where s t r e s sed vowel duration is seen to decay markedly a s a

function of word length, Final lengthening i s not limited to phrase

final position as additional data have shown. A tentative interpreta-

tion of this fact would be that this effect may be an attribute of the

word.

Summary of Results

F o r unstressed syllables i t was found that

(a) the acoustic duration of a segment i s approximately con- stant;

(b) the acoustic duration of a segment i s longer i n final posi- tion than i n initial and medial positions.

F3r s t r e s sed syllables i t was found that

(a) the acous t ic segment duration is approximately equal to its unstressed duration plus a n increment due to the superim- posed s t r e s s ;

(b) i n initial position the value of this stress-dependent in- c rement is inversely proportional to the number of syl- lables of the word;

( c ) i n final position the duration of a s t r e s sed segment is likewise lengthened.

In Fig. I-A-4 an attempt is made to quantify the effects observed

i n t e r m s of a simple mathematical model. As can be seen vowel sag-

ment duration V is given a s

where d iepresents a constant duration character is t ic of unstressed vowels i n init ial and medial positions within the w o r d and D represents

I I I I I

,UNSTRESSED VOWEL - C a 1 v = d

- vf = d.k -

- -

- Initial &- and Medial

I I I I I ,

I I I I I -

- STRESSED VOW EL [a:]-

-

-

- -

V = d + D/n

I I I I I

1 2 3 4 5 1 2 3 4 5

NUMBER OF SYLLABLES PER WORD

Fig. I-A-4. The previously presented data a r e summarized by means of a simple mathematical description according to which vowel seg- ment duration, V , i s given by V = (d + ~ / n ) k , where d repre - sents a constant duration character is t ic of vowels i n unst ressed syllables and D i s a n increment due to the superposition of main s t r e s s and n the number of syllables per word. k i s the position- dependent factor which ie > 1 (final position) and 1 (otherwise).

STL-QPSR 2-3/1968

an increment due to superimposed s t r e s s and n the number of syllables

pe r word. k is the position dependent factor which i s > 1 (final posi-

tion) o r 1 (otherwise). It is possible to regard the t e r m ~ / n a s reflec-

ting the well-known principle of isochrony o r equalization(4), that is,

the tendency for an utterance unit to assume constant total duration

i r respect ive the number of segments that the unit is made up of.

Discussion

It was suggested above that the lengthening of segments in final syl-

lables might be a property of the Swedish word. Other explanations

can a lso be suggested to account fo r lengthening i n phrase-final posi-

tion. Investigators have noted for many languages that the subglottal

p res su re and the fundamental frequency of phonation and acoustic

amplitude remain relatively stable i n the beginning of an utterance but

tend to fall a t the end of a normal declarative sentence. The under-

lying phonatory and articulatory activity is assumed to be character ized

by a general relaxation of speech gestures towards the end of an ut ter-

ance. This pattern has been te rmed normal breath-group ( 6 ) o r basic

ph rase contour (7). In his model of word and sentence intonation

presented a t the 6th ICA i n Tokyo a h m a n postulates the existence of

an abs t rac t "physiological intensity contour" that underlies the ob-

served variations of subglottal p res su re and fundamental frequency.

It i s constant during the beginning of an utterance but then falls towards

the end. It is fur ther assumed that

(a) the physiological energy expended p e r syllable is constant (apart f r o m variations with s t r e s s and, i n s t r e s sed syl- lables, with word length), and

(b) that this energy is equal to the t ime interval of the so-called "physiological intensity'' over the duration of the syllable.

Granted the assumption of the energy p e r syllable being constant

final lengthening of segments becomes a consequence of the intensity

being lower i n the final par t of the basic phrase contour,

Effect of Inherent Fea tures

In Fig. I-A-5 note also that rowels like [a:] arid [i:] although

character ized by differences i n so--called inherent duration behave

s imilar ly under these prosodic perturbations and fit the description just

given. To account f o r the dependence of vowel duration on vowel iden-

tity some investigators have suggested principles of energy expenditure

ARTICULATORY INTERPRETATION OF VOWEL DURATION

DRIVING FORCE DISPLACEMENT MIDSAGITTAL SEPARATION

OF LIPS

HALF-OPEN

CLOSE

0 23' ..:..s LOWER ..... -4...,

LIP t +

. JAW

Fig. I-A-6. Idealization of the dynamics of lip and jaw movement in a [bVb] type of syllable. The model predicts that the acoustic duration of a vowel i s a function of i t s degree of m a n d i b u l a ~ opening.

. .,

STL-QPSR 2-3/1968 5.

s imi lar to those given above (3) . Our own approach to this problem has

consisted in constructing a model of l ip and mandible coordination that

gives a mechanical interpretation of the durational variance of vowels

( see Fig. I-A-6).

In this model the lips a r e represented by damped spring-mass I systems. The rectangular input forces corresponding to a hypothet-

ica l [ b ~ b ] utterance a r e shown to the left of this figure and the r e s - !

ponses i n the middle. The displacement of the lips and jaw determine

the course of the midsagittal separation of the lips. Vowel duration

is equal to the interval during which this parameter is l a r g e r than

zero. The right par t of the figure shows the course of the separation 1

a s a function of jaw opening. It is seen that vowel duration increases

with l a r g e r jaw opening. The point we want to make with this graph

is that the variations of acoustic vowel duration may have a mechan- I

i ca l cause, namely the iner t ia of the jaw.

References

(1) Meyer, E. A. : "Zu r Vokaldauer i m Deutschen" (Nordiska studier I

tillegnade A. oree en) (Uppsala 1904), pp. 347 -356.

(2) Ohala, J. and Hirano, M. : "Control Mechanisms for the Seq-cleric- ing of Neuromuscular Events in Speechtt , paper C4, 1967 Con- I ference on Speech Communication and Processing, Cambridge, I Mass. 6-8 Nov. 1967.

(3 ) Jespersen , 9. : Lehrbuch d e r Phonetik ( ~ e i ~ z i ~ / ~ e r l i n 1926).

(4) Abercrombie, D. : Elements of General Phonetics (Edinburgh I

1967).

(5) Eler t , C -C. : "Bidrag t i l l en fonematisk beskrivning av svenskan", Arkiv f o r Nordisk Filologi 72 (i957), pp. 35-60. -

(6) Lieberman, P. : Intonation, Perception, and Language (Cambridge, Mass. 1967).

(7) ahman, S. E. G , : "Word and Sentence Intonation: il Luantitaiive Model", STL-LPSR 2-3/1967, pp. 20-54.