Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

A descriptive model oflaryngeal articulation in

speechLindqvist-Gauffin, J.

journal: STL-QPSRvolume: 13number: 2-3year: 1972pages: 001-009

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

STL-QPSR 2-3/1972

I. SPEECH PRODUCTION

A. A DESCRIPTIVE MODEL OF LARYNGEAL ARTICULATION IN SPEECH

J. Lindqvist

Abstract

In a previous paper(i) we have suggested a two-dimensional model of laryngeal articulation for production of phonatory types used in different languages. A mechanism for controlling downward pitch inflections was also discussed. The model was based on observations made with fiber optics inserted through the nasal passage(2). The philosophy of the model was that laryngeal speech mechanisms a r e closely related to more basic, phylogenetically old, laryngeal mechanisms associated with breathing, phonation, and protection. Essentially the same ideas a r e used in the present paper to describe more explicitly the function of the larynx in t e r m s of a hypothetical model.

Introduction

The laryngeal muscle s a r e organized in functional groups. Each muscle

ac t s in one o r more of these groups. An independent control of a single

muscle i s a difficult task, although not impossible, but can be regarded a s

a l e s s natural activity. In order to develop such activities it i s necessary

to have an accurate control of the resul t of the action by means of, for in-

stance, acoustic feedback. However, in speech communication a very p re -

cise control of the acoustic signal i s neither possible nor necessary. P e r -

ception makes use of the redundancy inherent in speech which allows great

variability in the signal. Coarticulation effects a r e therefore generally not

compensated for(3) and thus the speech apparatus i s f ree within l imits to

produce the speech in the most natural way. In the search for these natu-

ral articulatory gestures which it may be reasonable to look for among

those which a r e innately organized, o r thc basic laryngeal gestures, the

phylogenesis of the larynx may give valuable information. Unfortunately

there a r e divergent opinions about the nature of the basic laryngeal func-

tions. We therefore s t a r t our discussion with some aspects of the evolu-

tion of the human larynx. The conclusions made in this paper a r e p r imar - ily based on our own observations with fiberoptics, but facts found in the

(4) l i terature a r e also considered .

STL-QPSK 2-3/1972

Basic laryngeal functions

An important fcnction of the larynx i s to work a s a sphincter. Phylo-

genetically this sphincter exhibits two functions, one related to a i r -trapping

and one to protection of the subglottic system. We will argue he re that in

thc human larynx these two functions make use of the same laryngeal mech-

ar.ism. The a i r -trapping inlet and outlet valve s have been the t rue and

false vocal fold;, r e spectively. Ah-trapping, which has some influence

on the pectoral girdle function in, for instance, the apes when swjnging

from a branch(5) i s not important for human beings. Instead the t rue vocal i

folds have been specialized for phonation and the retrogression of the false I

vocal folds has made these s t ructures l e s s efficient a s a valve for a i r -

trapping. Effective air-trapping in the human larynx i s in our opinion a l -

ways supplemented by the mechanism of the protective closure. This

c losure i s a t a level above the glottis and i s made between the tubercle of (6) the epiglottis, the cuneiform carti lages, and the arytenoid carti lages .

In Fig. I-A-I a scquence of f r ames f rom a fi lm registration of this type

of laryngeal closure i s shown. Our experimental observations indicate

that breath-holding i s often performed with the r e spiratory muscle s and

not by closing the larynx, but sometimes, a s e. g. if the intrathoracic

p res su re i s ra ised, a s when someone coughc, this protective closurc i s

used.

The larynx i s a lso active during respiration(7). This activity i s found

in the muscles that adduct and abduct the glottis. The adducted state of E

the glottis i s used for phonation. Evolutionary evidence indicate s that

phonation i s not exclusively connected with speech (see ref. 5). Conse-

quently it seems reasonable to conclude that the adducted state of the

glottis, the "voicing position", i s a basic and language independent larynge-

al function.

F r o m the discussion given above we can identify three basic laryngeal

functions related to breathing, - phonation, and protection. The co r re spond-

ing postures o r positioning of the larynx a r c the breathing position, the (8) voicing position, and the protective closurc . Innately organized muscle

groups a r e used for movements intermediate and superimposed on these

postures. The movement f rom the open position (breathing position) to

the voicing position i s called glottal adduction and the movement f r o m the

voicing position to the open position i s called glottal abduction. The muscles

STL-QPSR 2-3/1972 3.

used for these movements a r e poster ior crico-arytenoids which abduct

the vocal folds, and the inter -arytenoid muscle which adducts the vocal

folds. EMG-measurements indicate that probably no other muscle ac t i -

vitie s a r e nece s sa ry for the se movement n(O) although it i s traditional to

attribute an adducting function to several intrinsic laryngeal muscles.

The observed movements of the arytenoids a r e a rocking o r rotatory

moverr.ent around the cylindrical joint on the crizoid carti lage in a dorso-

la te ra l direction.

Movements f r o m ei ther the open o r the voicing position to the protec-

tive closure a r e made by inhibiting the crico-thyroid muscles and by a c -

tivating al l sphincter muscles of the larynx including the ary-epiglottic

sphincters. The ary-epiglottic sphincters a r e here defined a s the a r y -

epiglottic, the oblique arytenoid, the thyro-epiglottic, and the external

t hyro-arytenoid muscles( lo). In our opinion the ary-epiglottic sphincters

a r e of p r imary importance. The movements of the arytenoids f rom voic-

ing position to closed position take place in a forward tilting direction to-

wards the tubercle of the epiglottis("). The tubercle of the epiglottis is

a t the same time pulled dorsally, by a rotation of the thyroid carti lage

about i t s joint, and approaches the arytenoids.

Evolution of language and speech has a l so made use of a functional

differentiation of the sphincter muscles which has enabled a fine control

of pitch and phonation types. This we will discuss in the following section.

Thc role of the extr insic muscles on laryngeal articulation i s l e s s known;

probably they take an important par t in the regulation of pitch and pos-

sibly a l so in the protective closure(i2). Ilowever, it seems reasonable

to assume that even for pitch regulation thc intrinsic laryngeal muscles

(including crico-thyroidcus) a r e of pr imary importance and we will r e -

s t r ic t our discussion to these muscles.

Laryngeal speech functions

So f a r we have discussed the basic laryngeal mechanisms. Breathing,

protection, and phonation have been considered. Now we will turn to thc

question how these mechanisms may be utilized in speech.

The speech posture of the larynx i s \-?it11 the vocal folds in voicing posi-

tion. In this position the vibrations of tlie vocal folds a r e most easily sus-

tained but if the a i r velocity i s sufficient they can a lso vibrate in a more

STL-QPSR 2-3/1972 4.

open position. The laryngcal speech gestures a r e dynamic in their nature

and they appear as a modulation of the spccch posture.

Three functions of the larynx of communicative importance a r c d i s -

cussed here: to dcvoice, to change the quality of the voice, and to control

the pitch. There a r e two types of devoicing gestures which secm to be

used by speakers of any language. These a r e the glottal abduction gesture,

that i s an articulation towards the open position of the larynx (breathing

position), and the laryngeal closure gcsturc, which i s art iculated towards

thc closed larynx position (protective closure), see Lindqvist, ref. 1.

An example of an almost complete laryngeal c losure is given in Fig. I-A- 1.

The muscles activated for the abduction gesture a r e the poster ior

c r ico -arytenoidei and for the adduction ge s ture the inter -arytenoideus.

The laryngeal closure gesture i s p e r f o r ~ e d by activating a l l sphincter

muscles a s described in the previous section. The degree to which these

gestures a r e invoked in speech i s determined by the acoustic resu l t s

aimed a t , and they ncver reach the breathing or completely closed posi-

tion. In voiced contcxt a more extreme laryngeal closure gesture resu l t s

in a voiceless interval, and i s generally r e fe r red to a s a glottal stop.

A s already pointed out, the vocal folds may vibrate even in a somewhat

open po sition if the a i r -velocity through the glottis i s sufficient. Accord-

ingly, abduction gesture performed to suppress the voicing in voiced con-

text may cause cxccssivc los s of a i r . The abduction gesture i s therefore

efiectivc a s a dcvoiccr only in combination with an o ra l constriction while

%e glottal stop gesture can be used a s a dcvoicer independent of other (13) ar t iculators .

Th- glottal abduction gesture and thc laryngeal closure gesture can a lso

be used to change the quality of the voice. According to our hypothesis

these gestures a r e independent a t a motor command level and different

combinations of them may be used a s phonatory types of laryngeal ar t icula-

tions in different languages. A small degrec of glottal abduction tends to

decrease the closcd phase of the vocal fold vibrations ( increase the open

quotient). T h e acoustic consequence of this i s a reduction of the amplitude

of the higher and that the voice obtains a more o r l e s s noisy

character. In phonetic t e r m s this type of voicing i s often re fer red to a s

lax voice o r breathy voice(i5). A laryngcal closure articulation has a -

STL-QPSR 2-3/1972 5.

quite different effect on the quality of the voice. The increase of the a c -

tivity in the ary-epiglottic sphincters resu l t s in a shortening and thickening

of the vocal folds and if the activity in the vocalis muscles was not in-

c reased , this would resu l t in a lowering of the pitch. However, a s defined

ea r l i e r a laryngeal closure gesture i s accompanied by an increased activi-

ty in the vocalis muscles. This activity counteracts the effect the short-

ening of the vocal folds has on the pitch. The vocal folds a r e also pressed

together which cause them to vibrate with a decreased open quotient. A

more extreme articulation resu l t s in i r regular periodicity of the vibrations

o r in a complete suppression of the vibrations, depending of the p res su re

drop a c r o s s the glottis.

The consequence on the acoustic signal i s increased intensity of the

higher harmonics , s imilar to the effect of an increase in the subglottic

pressure . This type of voice i s often re fer red to a s tense voice. The a -

periodicity gives the voice a rough charactcr and this i s often called

creaky voice o r creak (see Ladefoged, 1967, and Catford, 1964, ref. 15),

depending on the degree of aperiodicity.

The same acoustic features in combination with consonant articulation

a r e often described a s laryngealized sounds and sometimes a l so a s glot-

talized sounds. We choose to use the t e r m laryngealization to define a

laryngeal articulation towards the laryngeal closure. A glottal stop i s ( 16) then an extreme case of laryngealization .

The evolution of language and speech has made use of an independent

pitch control mechanism by a functional differentiation among the sphincter

muscles of the larynx. F o r regulation of the pitch i t i s essent ial to have

control of the activity of the vocalis muscles , independent on a motor

command level, of abduction and laryngealization ge sture s. The hypo-

thesis has been put forward that laryngealization in combination with low

vocalis activity i s used a s a mechanism for producing a low pitch voice

a s in the Swedish word accent ( see ref. 1). More recent data collected

with fibcroptics seem to verify this These data a l so in-.

dicate that a laryngeal closure can be performed without the assis tance

of activity in the vocalis muscle. IVe suggest that this type of laryngeal

c losure, which i s s imilar to laryngealization but with no activity in the

vocalis muscles , should be called laryngeal constriction. According to

Fig. I-A-2. Selected f r a m e s f r o m a f iberscope f i lm r e g i s t r a - tion of connected speech, showing the larynx for low (a) and high (c) pitch. Glottal abduction a t low (b) and high (d) pitch i s a l so shown.

Whispering

adduction *t-- Glottis -* abduction

All languages (but not phonemic)

Ladefoged' s phonatory types in relat ion to laryngealization and glottal abduction

All languages

3nvoiced

adduction 4- Glottis + abduction

p Gujarnti Breathy voice

Indone s ian 4

Lax voice

r : . 0 .A C,

fd N

.PI 4 rd Q, bO c 2- rd 14

*

Catford' s phonatory s t r i c tu re - types in re la - tion to laryngealization and glottal abduction.

Korean

All language s

Voice

Fig. I-A-3. Tentative two-dimensional descr ipt ions of laryngeal ;irticulation of phonatory types used in different lan- guages. According to m o r e recent f ind ings t he vocalis activity may be i l lus t ra ted separated f rom laryngeali- zation in a th i rd dimension (Lindqvist, 1969).

Hausa

Glottal stop

f Kumam

Tense voice Murmur

J

Unvoiced

(vo ice less )

Voice

Norma l glottal

(Voice)

Creak

Kumam

Creaky voice

Tense voice

Ligamental

(Voiced

Creak

Ventricular

(Creak)

Lax voice Breathy voice

(Breathy voice)

?

(Stop) Glottal stop

Murmur

Arytenoidal ?

creak)

Creaky voice

(Whispery voice)

Whispering

(Whisper?

e-) Whispery c r eak

STL-QPSR 2-3/1972

4. T h e g l o t t a l s t o p g e s t u r e i s i n t e r p r c t e d a s a g e s t u r e towards the protective closure and laryngealization i s defined with reference to this basic laryngeal mechanism.

5 . A mechanism for controlling low pitch and downward pitch inflection i s described which makes use of the ary-epiglottic sphincters.

There a r e , of cour sc , some uncertainties regarding the validity of the

suggested model due to laclc of EMG-data. This i s especially t rue for the

ary-epiglottic sphincters which have not been discussed previously in con-

nection with speech production. Also the role of the extr insic laryngeal

muscles i s not considered in the present model ( l9 ) ,

However, our model seems to account for the most essent ial functions

of the larynx, The described physiological and acoustical relations be - tween low tone, laryngealizatioli, and glottal stop may give a better under -

standing of dialectal variations and his tor ical change s in language s using

low tone. One exam* of such variation is the different realizations of the

word intonation in Danish, f rom low tone, extfcmely low tone to glottal

stop. Another example i s the historical change that seems to have taken

place in the Peking dialect of Chinese . In this case a final laryngealized

s top consonant has developed into a glottal stop which in turn h s s developed

into a low falling tone,

Two examples of how this model can be used for linguistic purposes a r e

shown in Fig. I-A-3. This figure shows tentative two-dimensional de scr ip-

t ions of laryngeal articulation of phonatory types used in different languages,

suggested by Ladcfoged and by Catford (see ref. 15). The two dimensions

used a r e the glottal abduction and laryngcalization. A better description

can be made with the vocalis activity in 3 third dimension, although the

present simplified description seems to capture the most essential linguist-

ic facts.

References

( 1) Lindqvist, J. : "Laryngeal mechanisms in speech", STL-QPSR 2-3/1969, pp. 26-31.

(2 ) Sawashima, M. and Hiro se , H. : "New laryngoscopic technique by use of fiber opticsf ' , J.Acoust. Soc.Am. - 43 (1968), pp. 168-169.

( 3 ) Intrinsic allophones occur by definition due to coarticulation with the context. An interesting question is i f language ever make use of corn- pensatory articulation in specific context in o rde r to maintain cer tain acoustic features. J. Lindqvist, Intern repor t 31. 1. 1969 (in Swedish). It can, for instance, be shown that the interaction f rom articulatory

STL-QPSR 2-3/1972 8.

cont. re f . (3)

and pulmonary gestures on the pitch in speech a r e not compensated for. See Ohman, S. and Lindqvist, J. : ' 'Prosodic pitch contours", Z. f. Phonetik usw. - 2 1, Heft 1/2 (1968), pp. 163-170.

(4) Laryngeal features a r c not discussed since in our opinion the ab- stractions made in feature systems a r c not capable of giving a full understanding of the speech proce ssc s . The theories of distinctive features have a lso resulted in a conc.cntration of too much effort on the descriptive needs of the linguist instead of on finding the l imita- tions and intrinsic character is t ics in the speech mechanisms which in it self may have explanatory powcr . Lindblom, B. : "Phonetics and the dc scription of language", to bc publ. in the Proc . of the VIIth International Congress of Phonetic Science s , Montreal, by Mouton & Co. (forthcoming).

(5) F o r a discussion; see pp. 98 -1 12 in Ncgus, V. E . : The Comparative Anatomy and Physiology of the Larynx o on don 1949).

( 6 ) The epiglottis, which i s a rudiment, does not function a s a lid to close the larynx a s sometimes i s stated. Only the lower pa r t , the tubercle of the epiglottis, takes par t in the closure. However, the laryngeal closure ge s turc has a tendency to obscure the view of the larynx by a backward. t i l t of thc epiglottis.

(7) Faaborg-Andersen, I<. : Electromyographic Investigation of Intrinsic Laryngeal Muscles in Humans (Copenhagen 1957) p. 18.

(8) The opinion that thc human larynx i s a three -tied sphincter (P res sman , 1954) i s according to our observations wrong. The third level of l a r - yngeal closure should, according to that hypothesis, be a t the level of the false vocal folds. The size of the false vocal folds var ics bc - tween different individuals and i t i s not unusual to find subjects that can put their false vocal folds into contact and even phonate with them. However, this i s not very common and cannot be regarded a s a basic laryngeal function. On the other hand, the false vocal folds nlay play a secondary role in the protective closure and a c t a s a cushim to complete the closure between the tubercle of the epiglottis and the arytenoids. The false vocal folds contain only few muscle f ibers and the positioning of the sc folds i s determined by the surrounding s t ructures like the ary-epiglottic sphincters. (See P r e s s m a n , J . J. : "Sphincters of the. larynx", A. M. A. Arch. of Otolaryngology - 59 ( 1954), pp. 22 1-236. )

(9) Hirose, H. : "An electromyographic study of laryngeal adjustments during specch articulation", Haskins Laborator ies SR-25/26 ( 197 I ) , pp. 107-116; Hirose, H. and Gay, T. : "The activity of the intrinsic laryngeal muscles in voicing control: An electromyographic study", Hrrskins Laborator ies SR-28 (1971), pp. 115-142.

(10) Unfortunately speech r e s e a r c h e r s have paid no attention to these muscles and no EMG-data on their functions a r e available.

( 1 I ) Sone sson, B. : "Die funktionelle Anatomie de s Cricoarytaneoidgelenke s t ' , Z . f. Anatornie und Entwicklungsgc schichtc 12 1 (1959), pp. 292 -303; - Kaplan, H. M. : Anatomy and Physiology of Speech (New York 1960), p. 154. van Leden, H. and Moore, P. : "Tlle mechanism of the crico-arytenoid joint", Arch. Otolaryng. (Chic) 73 (1961), pp. 541 -550.

STL-QPSR 2-3/1972 5.

Nasser Kotby, M. and Haugen, L. I<. : "The mechanism of laryngeal functionti, Acta Otolaryng. 70 (1970), pp. 203-211; Faaborg-Andersen, K. and Sonninen, A. : "The function of the ex- t r ins ic laryngeal muscles a t different pitcht' , Acta Oto-Laryng. - 51 (1959), pp. 89-93; Sonninen, A. : "The external f rame function in the control of pitch in the human voicei' , Ann. of the New York Academy of Sciences - 155 (1968), pp. 68-90.

The hypothesis has been suggested that a stiffening of the vocal folds in combination with glottal abduction i s used a s a mean to stop vocal fold vibrations for the production of voiceless consonants (Halle and Stevens, 197 1). Even if such an articulation should give the expected resu l t it i s not likely that it occurs due to the functional organization of the laryngeal muscles. Fur thermore EMG-measurements have shown that the activity in thc vocalis muscles i s generally dccreased for consonant articulations (Hirose, rcf. 9). Halle, M. and Stevens, K.N.: "A note on laryngeal features", MIT, QPR No. 10 1 ( 197 i ) , pp. 198 -2 11.

Lindqvist, J. : "The voice source studicd by means of inverse filtering", STL-QPSR 1/1970, pp. 3-9.

Ladefoged, P. : "Linguistic phonetics1', Working P a p e r s in Phonetics 6 (UCLA), 1967, pp. 1-98; Catford, J. C. : "Phonation types: Thc classification of some laryngeal components of speech productionr', in In Honour of Daniel Jones (London 1964)) pp. 26-37.

Both the glottal abduction gesture and the laryngealization gesture a r e covered by the linguistic feature "glottal s t r ic ture" (Ladefoged, P. : "The h r e e glottal feature s t ' , Working P a p e r s in Phonetics 2 (UCLA), 1972, pp. 95-101). This description of what i s going on may satisfy some linguistic purposes, but for a complete theory about speech and language, a more detailed description of the use of the larynx i s needed.

In another feature system used by Halle and Stevens ( 1967, ref. 13) the t e r m "constrictcd glottisf ' i s uscd to represent a n adjustment which

'kauses the vocal cords to b e pressed together andthe glottis to narrow o r to close". In our opinion the mechanism behind this type of ar t icula- tion i s laryngealization a s defined in this paper. However, we prefer the t e r m laryngealization, because i t does not emphasize what happens with the glottis and the general use of the word seems to be in accord- ance with our definition.

Lindqvist, J. : !'Laryngeal articulation studicd on Swedish subjects", I

this issue of the STL-QPSR.

A glottal stop gesture i s generally accompanied by a creaky onset and offset of voicing. Thus extreme lo\-/ pitch and glottal stop have both acoustical and physiological similarit ie s , which may explain, for in- stance, the dialectal variation in thc realization of the Danish "stbd".

Ohala, J. and Hirose, H. : "The function of the sternohyoid muscle in speech1', Ann. Bull. , Re search Institute of Logopedic s and Phoniatrics 4 (1970), Univ. of Tokyo, pp. 41 -44.