PROLEGOMENA TO THE INVESTIGATION OF LABIAL-VELAR STOPS IN FONGBE(1)

by Bertin C. YEHOUENOU

 

Abstract

Assuming that labial-velar stops are double articulations, the author investigates their nature in relation to these sounds in FONGBE, a Benin language in West Africa. He also provides experimental evidence through spectrographic records and concludes that these labial-velar stops have distinctive transition and locus.

En supposant que les Occlusives labiovélaires sont des doubles articulations, l'auteur se propose d'étudier la nature véritable de ces consonnes dans le FONGBE, une langue du Bénin, en Afrique de l'Ouest. Sur la base de quelques spectrogrammes, il montre que ces consonnes complexes sont différentes des Occlusives simples comme /‡p, k, b, g/.

INTRODUCTION

Attempts have been made to describe some of the uncommon sounds that occur in the languages of the world. One such sound is a stop consonant which is diversely referred to. In fact, terms as varied as --double articulation, doubly articulated stop, labiovelar stop, double articulated plosive, coarticulated stop, labiovelar articulation, labial-velar double articulation, labial-velar stop-- have been used to designate it. Indeed, the sound at stake is a stop consonant, an oral stop consonant. The most common of its type is made on an egressive pulmonic airstream mechanism. It can be voiceless as well as voiced.

Apart from classification and identification, very little is done to account for the production and interesting traits of this sound.

It is the purpose of the present study to investigate the nature of the labial-velar stops in FONGBE. This will be done in the light of previous research and experiment that have been undertaken by some investigators (such as Sarah GARNES and Peter LADEFOGED) and whose object has been to make statements on both the articulatory and acoustic characteristics of labial-velar stops in languages like YORUBA and IBIBIO.

STOP ARTICULATION AND DOUBLE ARTICULATION

As far as plain oral stops are concerned, they are produced in the following way : the soft palate is raised so that the nasal cavity is closed. There is an articulatory closure, the location of which depends upon the active and the passive articulators involved, which in turn effect the quality of the oral stop concerned. It can be labial, dental, alveolar, retroflex, palatal, velar, uvular, glottal. Therefore the airstream is completely obstructed. Pressure then builds up behind the closure and an oral stop is formed. When the articulators come apart, the airstream is released in a burst which is not always audible. This processus is best explained by the three-phase distinction which is found in phonetic theory literature. ABERCROMBIE (1967:147) for example, speaks of the three phases in the production of oral stops and says that this distinction is important in the function of stops in connected speech. The three phases are: (fig. 1)

We can see, in the FONGBE consonant chart, that plain oral stop consonants occur in the language. Those have been clearly described as using the same airstream mechanism, that is the egressive pulmonic airstream mechanism. They then display much of the pattern described in plain oral stops in the languages of the world. The sounds concerned are : / ‡p, b, t, d, d, c, j, k, g/, that is nine plain oral stops in number.

As to /k‡/ and /~b/ which also appear in the stop inventory of FONGBE, little is known about the mechanism of their production apart from tentative, uncommitted descriptions. We can only note that FONGBE has both voiceless and voiced double articulated stops, which at first seem to be in contrast with voiceless bilabial /p/ and voiced bilabial /b/ respectively and also in contrast with voiceless velar stop /k/ and voiced velar stop /g/ respectively.

CLASSIFICATION AND DISTRIBUTION

General surveys of African languages often list a series of traits which are said to be characteristics of sub-sahara Africa as a linguistic area. These enumerations tend to include, among other things, phonological features such as tone, click sounds, implosives, labial-velar stops and the prevalence of open syllables. Of the characteristics many are in fact found in other world areas. For instance, a preference for open syllables or tone. A few, however, are confined to Africa such as click sounds which are not of wide distribution since they are found only in South Africa. Others are common in Africa and are found in other places. An example is labial-velar stops which are the sounds under discussion here.

Phoneticians often compare labial-velar stops with plain stops with a view to working out any significant similarities or differences. WELMERS, quoted by GREENBERG, states that :

Ian MADDIESON (1984) for his part, observes that stops occur in the inventory of all known languages and have appropriately been regarded as the optimal consonant (JAKOBSON and HALLES,1956:42). But he goes on to observe that labial-velar stops are only found in twenty languages and represent 6.3 per cent and mostly in African languages such as IBIBIO and YORUBA.

GREENBERG (1970) says that here is an area outside of Africa in which these sounds are found and that is the Kate ono group of non-Austronesian (Indo-Pacific) languages in north-eastern New Guinea and some Austronesian languages of Melanesia have these sounds. In this respect, this remark by GREENBERG seems important which says that :

ARTICULATORY ASPECTS

Many assumptions are made as far as the articulations of labial-velar stops are concerned. Some say that the coarticulated stops change most commonly to labialised velars, velars, or labials and often to more than one of these in the same language depending on adjacent, usually following vowels. Westerman, for example, assumed that labial-velar stops, in his western Sudaniclanguages, were not original but arose everywhere from labialised velars, that is sounds of the /kw/ type. Unfortunately, he did not give any form of evidence.

Articulatorily, labial-velar stops have been described as involving two simultaneous articulations, a bilabial one and a velar one. Hockett is quoted by LADEFOGED (1968:11) to have indicated that the only known kind of coarticulation is that involving simultaneous labial and velar strictures. The involvement of the two articulations can also be justified by the way we now refer to the sound under discussion. We often find the term 'labio-velar' used for 'labial-velar' as for example in GREENBERG (1983). LADEFOGED (1971 : 59) suggests that, in terms of the usual conventions of systematic phonetic terminology, 'labio-velar' can only mean the physiologically impossible juxtaposition of lower lip and velum. Therefore the accurate term would be 'labial-velar'.

ABERCROMBIE tries to simplify the double articulation mechanism and presents it in terms of passive and active articulators. In fact, the passive articulators, he says, are the upper lip and the soft palate (which are said to be passive simultaneously). The lower lip and the back of the tongue are simultaneously active articulators.

As we can see, both ABERCROMBIE (1967 : 64-65) and LADEFOGED (1971 : 59) explain these doubly articulated stops as involving two degrees of stricture of equal importance. LADEFOGED (1971 : 59) goes on to state that labial-velars can involve simultaneous stop, fricative, nasal or approximant articulations. The oral stops, he says, like the nasal stops, are usually symbolised by the bilabial and velar symbols joined together by the tie bar, to indicate that the articulations are simultaneous and not sequential. This rejoins John LAVER 's description of labial-velar stops which he sees as being in contrast with plain velar stops for example in YORUBA. In his words, he sees these sounds as :

Besides, other types of labial-velar stops have been identified whose particularity is that they use and combine many airstream mechanisms. In fact, LADEFOGED (1968 : 9) discusses three different types of labial-velar stops. The first type, he says, employs a simple pulmonic egresssive airstream, the second combines this airstream with a velaric ingressive one, and the third one adds to these two a glottalic ingressive airstream. LADEFOGED makes these observations from experimental evidence using examples from Western African languages like YORUBA and he reaches the conclusion that the YORUBA labial-velar stops are of the second type. Sarah GARNES and Bruce CONNELL, for their part, have innvestigated labial-velar stops in another Nigerian language, IBIBIO, and they have reached the conclusion that the sounds under discussion are of the same kind as the YORUBA ones, the only difference being that they are voiceless in this language.

ACOUSTIC CHARACTERISTICS

So far we have seen some of the current ways of describing the articulations of labial-velar stops in the languages of the world. We have seen that two articulators are involved : the lip and the velum.

LADEFOGED (1968 : 12) says that there is an auditory resemblance between /kp/ and /gb/ and the corresponding velarised labial /p/ and /b/. This, in fact, relates to the acoustic characteristics of labial-velar stops which are clearly observable on a spectrogram. OHALA and LORENTZ (1978) have presented spectrographic evidence of this (w) quality. They have also argued that the presence of labialised velar stops /k/ and /g/ in addition to plain velar stops is common enough in the languages of the world to be of uncertain value in helping decide the categorisation of languages which happen in addition to have /kp/ and /gb/.

Sarah GARNES' own investigation has led to the conclusion that the labial-velar articulation consists of three phases:

-phase one is the onset consisting of low frequency, aperiodic vocal fold vibrations;

-phase two corresponds to the plosive gap which represents the period of silence;

-phase three is the release.

If we compare with the simple stops, we see that the onset phase is absent in the spectrogram of these simple stops ( that is /p , k/ ) and that they have positive voice onset time (V.O.T.). This feature can therefore be seen as a distinguishing feature of /kp/ .

Another interesting observation made by Sarah GARNES is that the release of /kp/ is prevoiced and is estimated to be an average of twenty-two milliseconds of voicing before the actual release. Besides, GARNES' results are particularly important from the point of view of determining both the transition and the locus of labial-velar stops in IBIBIO. She is only concerned, we may recall, with /kp/ . In this respect, she concludes that /kp/ is in fact distinct from /p/ or /b/ and /k/ with regard to its transitions and loci. She finds that the transitions associated with the release are rising, but steeper than those of plain bilabial stops, which, she says, suggests a faster transition, a lower locus, or both.

Similarly, commenting on the acoustic characteristics of YORUBA voiced labial-velar stops, LADEFOGED (1968 : 12) points out the rising transition of F2 on release, a rapid rate of transition, a tendency for the transition to have two loci, one at about 1.200 Hz and the other at about 2.200 Hz. This suggests that the bilabial release occurs first, and then the velar one.

Spectrographic records as gathered by Sarah GARNES, Peter LADEFOGED and Bruce CONNELL ( the three of them have investigated labial-velar stops) provide further evidence as to the asynchrony of the articulations involved in labial-velar stops (lip and velum). This becomes obvious when one combines, in an experimental situation, use of spectrogram and aerodynamic records. Thus, on the spectrogram, for example, the velar closure seems to precede the bilabial closure, closure which lasts for about twenty milliseconds (CONNELL, 1987).

Finally, we must note that Sarah GARNES was initially concerned to use the locus theory to account for the labial-velar double articulation. In fact, she succeeds since her results show that labial-velar stops are characterised by a distinctive transition and locus. In other words, the transitions of the three points of articulation --bilabial, velar and labial-velar-- are distinctive.

CONCLUSION

Before we draw any final conclusion on the characteristics of FONGBE labial-velar stops, a thorough study is necessary. One interesting undertaking is to examine such acoustic characteristics as formant location and transition, phonation and V.O.T. of the double articulation /kp/ and /~b/ by comparing them to simple stops /p/ and /k/ on the one hand, and /b/ and /~/ on the other. Therefore we see how useful it is to collect experimental evidence so as to be able to report on and account for any similarities or differences between the FONGBE labial-velar stops and the FONGBE plain stops.

NOTES

1 . FONGBE is a tone language. It is the language of the FON people in South Benin. It is one of five sections into which the GBE continuum has been broken down. GBE is classified under KWA languages which, in turn, belong to the NIGER-KORDOFANIAN family according to GREENBERG 's classification.

BIBLIOGRAPHY

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