Nasalization of Vowels in Relation to Nasals

THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 30, NUMBER 4 APRIL, 1958

Nasalization of Vowels in Relation to Nasals*

SHrug HATTORX, Department of Linguistics, University of Tokyo, Tokyo, Japan, K•.NGo YA•x•oTo, Department of Linguistics, University of Tokyo, and Kobayasi Institute of Physical Research, Tokyo, Japan

Os•Mrr Frrjmrmx, Kobayasi Institute of Physical Research, Tokyo, Japan (Received March 8, 1957)

The principal characteristic features of nasalization of vowels are (1) a dull resonance around 250 cps, (2) an antiresonance at about 500 cps, (3) comparatively weak and diffuse components which fill the valleys between the formants.

Features (1) and (3) are commonly found also during the period of oral closure of nasal constants, (3) in this case being influenced by the antiresonance of the oral cavity. The feature (3) affected by "antiformants" carries information about the tongue position during oral closure. If t. he nasal passage is stopped at the nostrils when nasalized vowels are pronounced, features (1) and (3) disappear, and the frequency of selective attenuation (2) is lowered. Some French and Japanese nasalized vowels have been examined and interpreted, applying the results obtained in the research.

INTRODUCTION

HE nasalized vowels are produced primarily by lowering of the velum, resulting in opening a side

passage for the air flow through the nasal cavity. This articulatory characteristic, which seems to be rather simple in mechanism, gives rise to complex modifications of the physical property of the sound, or in the sound spectrum. The spectra of the nasalized vowels have been investigated by many scientists, recently by means of the Sonagraph. •

We have employed i Sonagraph 2 as a sound analyzer and some other measures in order to ascertain the features, by which we believe the nasalization of vowels is identified.

1. CHARACTERISTICS SEEN ON THE SPECTROGRAM

1.1.

The effects of nasalization of vowels have been investigated. First, we examined the change on the sound spectrograms when the five Japanese vowels were pronounced and then suddenly nasalized, while keeping the articulation unaltered. The features of the nasalization of vowels seen on the spectrograms are

(1) re-enforcement of intensity in the region around 250 cps,

(2) weakening of intensity at about 500 cps, * This is the report of research at Kobayasi Institute of Physical

Research, Tokyo, Japan. • Potter, Kopp, and Green, Visible Speech (D. Van Nostrand

Company, Inc., Princeton, 1947); M. Joos, Acoustic Phonetics (1948), Language 24, No. 2, Suppl.; Jakobson, Fant, and Halle, Technical Report No. 13, Acoustics Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts (1952); M. Durand, Studia Linguistica 7, No. 1, 33-53 (1953); P. Delattre, Studia Linguistica 8, No. 2, 103-109 (1954).

• Sonagraph, Kay Electric Company. One at Kobayasi Institute of Physical Research was used for our study. The over-all frequency response is slightly modified from that given in the instruction manual of Kay Electric Company. For further details, see the paper by the present authors, Bull. Kobayasi Inst. Phys. Research 6, 226-235 (1956).

(3) appearance of comparatively weak and diffuse components between the formants of the vowels, particularly in the frequency region from 1000 to 2500 cps.

1.2.

In Fig. 1, examples of Sonagrams and the section patterns are shown. Each of the Japanese vowels was pronounced by Hattori, first orally, as in the usual pronunciation, and then fully nasalized. In the third step, keeping the velum down, the nostrils were suddenly closed with the fingers, the air flow through nasal cavity being completely stopped. The sound was taken up by a microphone at a distance of about 20 cm in front of the mouth opening.

We observed as a common consequence of nasalization (the second step in Fig. 1) that the second harmonic is re-enforced and, besides, the third (ca 500 cps) is weakened when compared with the others. When the nasal passages are closed (final step), the frequency position where the sound component is weakened shifts to a lower frequency portion (ca 350 cps).

Besides the characteristics (1) and (2), some other modifications in the spectrum are found when the vowels are nasalized. As a common trend for all the vowels, nasalization has an effect on the spectrum, which we could describe as filling the "valley" between the major formants by additional weak components which do not show any sharp resonance. The frequency regions where these weak components appear vary from vowel to vowel, and also from person to person generally, but there are certain frequency regions (see Sec. 3.3) where the components are apt to be re-enforced when the sound is nasalized.

1.3.

The observations by some investigators coincide on the point that nasalization is characterized by a re- enforcement of very low components or by the appear-

267

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268 . HATTORI, YAMAMOTO, AND FUJIMURA

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Fro. 1. Five Japanese vowels (H&ttori)

[a], Eli, [u], Eel, Eo]: oral vowels (usual pronunciation) E•], E•], En], Ee], Es]: nasalized vowels [• ], ['i ], [• ], ['• ], ['• ]: nasalbed vowels with closed nostrils.

ance of an additional bar in the bottom portion of the Sonagram. This characteristic feature is seen also in the nasal sounds in general. The spectra of the nasal consonants show simple resonance curves in this frequency region, whereas those of the nasalized vowels, which have lower resonances (first formants of the vowels), show somewhat complex curves in this region.

The peak of the resonance of the sounds Em], [n3, and [r•] is generally located at about 250 cps (Fig. 2). The resonance can be found also in the spectra of nasalized vowels clearly when they are compared with those of the corresponding oral vowels (Fig. 1). This resonance appears in the Sonagrams (or their section patterns) with the narrow band filter, as the re-enforcement of the second harmonic and its neighbors for

[m] En]

Fro. 2. [m], In], and [r•], with rising intonation (Hattori).

ordinary male voices, and of the fundamental for ordinary female voices.

We have checked the peak location more closely by examining the narrow band Sonagrams of the sounds pronounced with gliding pitch. Figure 2 shows Sona- grams of Em], En], and E•] with rising intonation, in which we can see clearly the resonant characteristics around 250 cps when we trace, e.g., the second harmonic upwards from left to right. This procedure has been followed in examining the pronunciation of several persons, both men and women, and the location of the resonance has been found not to be silCnificantly different for all the subjects? Similar Sonagrams have been taken for the nasalized vowels, too, and the corresponding resonance at the same position has been observed (Fig. 3).

This gliding tone method is also effective in defining the frequency of the selective attenuation, which in the case of usual nasalized vowels was found to be at about

a Because of the comparatively high damping of the resonance (see reference 6), accurate location of the peak of the resonance (not the peak in the spectrum of the sound emitted) cannot be given because the sound emitted is largely affected by the un- known characteristics of the vocal cords.


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NASALIZATION OF VOWELS IN RELATION TO NASALS 269

500 cps for several persons. 4 For the nasalized vowels pronounced with closed nostrils, the frequency is lowered generally down to about 350 cps. This point will be discussed in more detail later (Sec. 4).

When only the spectrum of sounds pronounced with constant pitch (as in Fig. 1) is examined, the details in the resonance or antiresonance characteristics of the

vocal tract are easily overlooked in the lower frequency region. For instance, in the Sonagram of nasalized I-i-[ in Fig. 1, the third harmonic does not seem to be weakened by nasalization, but we can find clearly the attenuation when the Sonagram of a sound produced with the gliding tone method is examined (Fig. 3). In case of I-i-[, there is no vowel formant in the region near 500 cps, and the sound from the nostrils (Sec. 3), which seems to be comparatively strong on account of the narrow passage in the oral cavity, appears conspicuously on the spectrogram, thus obscuring the attenuation (2).

2. PERCEPTUAL STUDY OF THE EFFECT OF ARTIFICIAL NASALIZATION

2,1.

To find the effect of the features described above on

the perceptual impression of the vowels in regard to their nasality, naturally pronounced oral vowel sounds were fed into a special electric filter system, in which the sounds were given the above-mentioned characteristics individually and in combination. The system we employed is outlined in Fig. 4.

According to the auditory impression of the authors and many others, the combination of the three features gives very good nasalization, even when compared with vowels pronounced with nasalization.

A fairly good effect is given by the two characteristics (1) and (2), in case of more open vowels. For the close vowels, I-i-[ and Fu-], however, the feature (3) seems to be more effective, and even necessary to secure the effect of nasalization. For wider vowels also, the impression of nasality usually becomes more natural when characteristic (3) is added.

The effects of (1) and (2) added separately are

Fro. 3. Nasalized Japanese [-T•, with rising intonation (Hattori).

• Varieties ranging from 400 to 600 cps, however, have been found for a few female voices.

Fro. 4. Block diagram of the filter system employed in the modifica- tion of natural vowel sounds.

VARIABLE

r TUNED- MI rep oduceAMP./•.TT. XERrecørO

somewhat different perceptually. (1) gives an impression of some nasality, but it is still far from perfect, while the effect of (2) by itself may hardly be noticed without special attention. The combination of the two characteristics produces the impression as if something new were added.

2.2.

A converse experiment was tried, ,iz., the naturally pronounced nasalized vowel sounds were artificially denasalized through a similar filter system with inverse characteristics. Due to the lack of proper instrumenta- tion, we examined the effect of features (1) and (2) only in this case. Successful results have been obtained for

more open vowels.

3. PHYSICAL INTERPRETATION

In the following we give a physical interpretation of the three features seen in the spectrum of nasalized vowels. This interpretation is also supported by some experiments described in the following sections.

3.1.

The re-enforcement at 250 cps is due to the resonance of the entire cavity from the glottis to the nostrils including the pharyngeal and nasal cavities as a whole. This re-enforced low sound is considered to be emitted

from the nostrils and presumably also through wall vibrations to the outside.

3.2.

The selective attenuation at about 500 cps is due to the antiresonance of the nasal cavity acting as a side branch connected to the major vocal tract at its midpoint. Due to the narrow opening and high dissipation at the front of the nasal cavity, the sound belonging to this mode and emitted through the nostrils to the open air should be comparatively obscure when compared with the sound emitted from the mouth opening especially for more open vowels, the pertinent frequency region of the latter sound being generally amplified (except for the local attenuation) by the pharyngo-oral resonance (the first formant) located at or near this region.


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270 HATTORI, YAMAMOTO, AND FUJIMURA

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.-.::•.:•,•. ............................. ..-•.--•.-,-•-?"•!'•:'":•"•"•'.

left water surface

FIG. 5. Sonagram (narrow band) obtained in the glass tube model experiment, showing the descending antiresonance (par- tially obscured by a superposed resonance), as a consequence of enlarging the side cavity.

The selective attenuation of a particular component by an antiresonance of a side tube can be demonstrated by a model experiment with a tuning pipe associated with a branched glass pipe. A tuning pipe was inserted at an end of the main glass pipe, the other end being open to emit the sound. At the midpoint of the main pipe (between the sound source and a constriction near the open end), a subsidiary glass pipe was attached vertically, making a side cavity. The lower end of the branch pipe was put into water in a glass cylinder held by hand. The level of the water surface which limits the volume of the side cavity could be moved down as the cylinder was lowered. As illustrated in Fig. 5, the frequency of the attenuation is lowered as the water surface is lowered, i.e., as the side cavity is enlarged. When the tip of the glass tube is out of the water completely, the frequency of the antiresonance jumps up abruptly. Conversely, if the open end of the side branch is stopped by a finger tip, the frequency is lowered radically. This corresponds to the effect of closing the nostrils with fingers while pronouncing the nasalized vowels. Further evidence corroborating our interpretation will be given in Sec. 4.

In connection with this experiment, it should be remarked that when the water level is lowered suffi-

ciently, a descending sharp resonance is recorded at the same frequency as the antiresonance. This is probably the resonance of the tube cavity emitted through the thin (1-mm thick) glass wall. This point is particularly interesting, because it is occasionally experienced that in some natural pronunciation, the wall separating a cavity from outside or another cavity does not actually insulate the sound completely, especially when the pertinent frequency region is very low. •

• Cf. K. L. Pike, J>honetics, A Critical Analysis of J>honetic Theory and a Technic for the J>ractical Description of Sounds (University of Michigan Press, Ann Arbor, 1947), p. 106. A. Sugawara also dealt with the wall vibration of the nose in his article, J. Oto-Rhino-Laryngol. Soc. Japan $7, 7-33 (1954).

3ø3ø

The effect of "filling the valley between formants" by minor components is due to the "leakage of sound" through the nasal cavity acting as a side channel. It is reasonable to assume that this channel has appreciable damping and complex vibration modes in the higher frequency region. This view has been verified by check- ing the spectra of nasalized vowels taken with a tiny microphone inserted at the nostril opening. Figure 6 shows some samples of such spectra. The complex resonance curves are seen to be substantially different - from the usual formants, and the figures as a whole appear somewhat different from the familiar patterns for the vowel sounds. The distinctive features of the

oral vowels are thoroughly obscured, and in fact, the sounds taken through the nostril microphone sound to our ears quite different from the usual vowels, the front vowels especially being completely beyond recognition.

In the section patterns of Fig. 6, we find the resonance of low frequency, which naturally corresponds to characteristic (1) of nasalization. As for the antiresonance (2), it is quite understandable that the selective absorption at about 500 cps is not found in the spectra of the sounds taken from the nostril. Some sharp valleys are seen in the section patterns, the location of which is generally higher and depends presumably on the tongue position. It is plausible to interpret these as the selective absorption due to the antiresonance of the oral cavity (Sec. 5.2).

It is thus reasonably assumed that the function of the nasal passages is more like that of a damped channel rather than that of a resonant chamber, as far as higher frequency regions are concerned. ø It is also reasonable to expect, however, that there would be some dull and complex resonances, which are due to the higher vibration modes of the nasal cavity, when the spectra of nasalized vowels or nasal consonants are examined more closely. Presumably, those should be the same for all the nasalized vowels and nasal

consonants, if the nasal cavity itself is not altered. In case of Hattori, for instance, a dull peak at ca 2300 cps

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Ea] Eo] Ea] E•]

Fro. 61 Sonagrams of the sounds recorded at the nostril while pronouncing the nasalized Japanese vowels (Hattori).

• The resonance (1) is very dull, it has a very low Q (3 or less), though it is rather conspicuous in Sonagrams or section patterns, due to the linear frequency scale.


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is usually found for nasalized vowels and nasal consonants, or at least it is consistent with our experience, to assume that there is always a weak resonance at that frequency, though sometimes it is obscured by the existence of a formant of the vowel in this region. Many other resonances of this kind might be found, but further description is omitted since it is doubtful if the details of these individual minor peaks are significant.

For the nasal antiresonance also, there might be many effects of higher modes. In the model experiment of the branched glass pipe described above, a higher mode of antiresonance has been recorded (Fig. 5), and in the spectra of the nasalized vowels as illustrated in Fig. 1, some minor local re-enforcement and weakening are found. They could be probably attributed to those higher modes, though they might also be caused by slight changes in the pharyngo-oral cavity. The higher the frequency, however, the less would be their effect on perception, because many such effects would be aver- aged. Moreover, the higher modes (of both resonance and antiresonance) would differ greatly from person to person, and if so, such features peculiar to the individual should be overlooked.

4. EXPERIMENTAL STUDY OF THE FUNCTION OF THE NASAL CAVITY

4.1.

The second characteristic feature of nasalization, which we have ascribed to the antiresonance of the

nasal cavity, has not been explicitly reported so far as we know, 7 and the appearance of the antiresonance in the spectra of speech sounds should be emphasized, because similar effects might be found in the spectra of the consonants in general, 8 though it is not plausible to claim that such effects are important perceptionally in every case. In case of the nasal cavity, the antiresonance has certainly an effect on the perception of nasality, as we have described in Sec. 2.l. In this regard, it would be worth while to confirm our view on the r61e of the

nasal passage by another sequence of experiments. In Fig. 5, we have found by a model experiment, that

the frequency of the antiresonance is lowered when the length of the side branch is increased. Correspondingly, it is expected that the location of the antiresonance will shift upwards, if the position of the stop in the nasal passage is shifted to an inner position. This was actually confirmed experimentally for Itattori and Yamamoto.

At first the outer points of the nostrils were stopped with cotton-like materials, immersed in ! % NaCl-water solution, and the nasalized vowels were pronounced with a gliding intonation. The Sonagrams obtained for the sounds pronounced in this way were found essentially the same as those obtained by closing the nostrils

7 A. S. House and K. N. Stevens refer to the introduction of an antiresonance in the frequency range 700-1800 cps in their electric analog experiment, J. Speech Hearing Disorders 21, 218-232 (1956).

8 See Jakobson, reference 1. Also see Secs. 5.2 and 5.3.

TABt. E I. Location of the antiresonance (cps).

Ea3 El3 Eu3 Ee3 Eo3

I Y. 550 550 600 (400)? H. 500 550(400)? 500

II Y. 350? 400? 350? H. 300 300 300

III Y. 500 300 350

H. 500(300?) 350? 350 IV Y. 500 ? 400

H. 520 ? 300 V Y. 900 550 650

H. 900 500 600

600 500 ? 500 450-500 350? 350? 300 300 300 350

? 350 ? 500

470 400 650 700? 600 700

I: Nasalized vowels.

II: Nasalized vowels with nostrils closed by fingers. III: Nasalized vowels with nasal passages stopped at outer

points. IV: Nasalized vowels with nasal passages stopped at midpoints. V: Nasalized vowels with nasal passages stopped at inner

points.

Y.' Yamamoto, H.-Hattori.

with the fingers. The antiresonance was generally located at about 350 cps. Data for two speakers are summarized in Table I.

Next the nasal passages were stopped at their midpoints by similar means. Similar Sonagrams were obtained, but the location of the selective absorption was found a little higher.

Finally, the inner point in the nasal passage was stopped, and in this case, the location of antiresonance was considerably high, and differed from vowel to vowel, even by a factor of two. This difference could be explained as due to the different position of the velum which is presumably affected by the level of the back of tongue, resulting in a different configuration of the nasal cavity in its innermost part.

The stopping of the passages was performed by a surgical specialist, and the configuration of the inner part of nasal cavity was found to differ considerably for the two individuals. Different procedures were empolyed for the inner stopping, and some discrepancies of resonant frequencies between the two persons are to be ascribed partly to this.

5. NASAL CONSONANTS IN RELATION TO NASALIZED VOWELS

5.1.

The articulation of the nasalized vowels and the

nasal consonants are both characterized by lowering of the velum, resulting in opening a side (nasal) passage for the sound. According to our physical interpretation, it is natural to expect that features (1) and (3) should appear also for the stationary part of nasal consonants.

5.2.

The higher components of the nasal consonants ap- pearing on the spectrograms, however, change their configurations depending on the tongue configurations and the points of articulation (i.e., the points where the


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Era] Era] Em] Era] Era] a i u e o

closed oven dosed oven dosed open dosed open dosed open

Fro. 7. Various [-m']'s with a small pipe inserted at mouth opening (Hattori). I-m-I, [-m'], etc.: a i

[-m'] pronounced with the tongue positions of [a-I, [i'l, etc.

oral channel is stopped). While stop•)ing the oral passage with the lips, many nasal sounds can be pronounced with different tongue positions. Figure 7 illus- trates such [-m•'s. In this case, a small pipe was inserted between lips, and while stopping the pipe opening with the finger tip, various [-m• sounds were pronounced; then the finger was abruptly removed, the sounds resulting in the nasalized vowels with the same tongue configurations.

It should be noted that when the pipe is closed, a characteristic valley is found in the spectrum (arrows in Fig. 7), but when the pipe is opened the valley always gets filled. The location of the valley, however, differs considerably from case to case in Fig. 7. This fact can be explained as follows. It is expected that the antiresonance of the oral cavity should appear in the spectra of some nasal consonants, as the converse effect of characteristic (2) for the nasalized vowels. The valleys mentioned above are manifestations of this effect. The narrower the back opening of the oral

the water level, without any change in the configuration of the pharyngeal cavity.

Filling the water up to the level of lips, [-m• was pronounced. Then, while keeping the same articulation, the water surface was lowered and the cavity size was increased. A narrow band Sonagram was taken, and a continuous shift of the antiresonance together with its higher modes down to the region of feature (3) has been clearly recorded as shown in Fig. 8.

5ø4ø

In case of the articulation of nasal consonants, the selective absorption of the oral cavity is usually not so simple as that of a uniform pipe. In some cases, the absorption might be one of the band attenuation type, rather than a simple resonance-absorption. The comparatively wide blank regions in the Sonagrams of nasal consonants, e.g. [-n•, are principally due to such an attenuation. In the case of [-m• with a neutral tongue position, a characteristic absorption is found

cavity, viz., the constriction made by the back of tongue, from 500 up to 1000 cps (see Fig. 2). In this case, the and also the larger the volume of the oral cavity, the. band width of the attenuation is narrower than that lower the frequency of the antiresonance. It is natural, from this point of view, that the articulatory configuration of [-o-] gives the lowest antiresonance, because the back of tongue makes a rather narrow opening at the back end of the oral cavity, while the lower position of the jaw produces a larger cavity. In the case of I-u], this volume would be much smaller than in [-o•, and this effect apparently overcomes that of the relative nar- rowness of the back opening.

5ø3ø

This point of view has been further confirmed by another experiment. The bent end of a glass tube (diameter 16 mm) was inserted into the mouth opening and was held tightly by the lips, so that there was no gap between lips and the tube wall. The tube.was held vertically downwards and was filled to a certain level with water through a siphon system. In this way, the oral cavity was extended to an additional cavity, and its volume could be varied by raising and lowering of

for [-n•, which has absorption in the region from 500 up to 1300 cps (400-1500 cps in case of Yamamoto). For [-r•-], on the other hand, no dominant absorption can be found, though the spectrum shows a complex and dull

'":'•?"J. J4-? '.Z'""•'•½?'"•? '•?•'/'/•'•::•?•:•:•:::•::•½:'"'?•:?•;•½•½½:•:::.• ..... •:•"'"':'•:'">'•:•::•½:•:;•½;•?•" '•::::::•'•::;J•:-;•:::7

Fro. 8. Effect of change in the volume of the oral cavity extended by a glass tube (descending antiformant) (Fujimura).


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frequency characteristic. In this case, the closure by the back of tongue is made near the back opening of the oral cavity, leaving a negligible volume as the side cavity. This consideration would lead us to the following interpretation: the spectrum of [• grossly represents the frequency characteristic of the pharyngo-nasal channel, if the characteristic of the vibration of the vocal cords

is disregarded. The spectrum of [m• or [n• is obtained when the frequency region characteristic of the pertinent articulation is deleted from the spectrum of The spectrum of [• differs considerably from person to person, presumably because of considerable variation of the shape of the nasal cavity. The feature peculiar to the individual, however, remains constant for Imp, In], and

The characteristic frequency region where the components are expunged by the antiresonance can be called "antiformant." In Sonagrams, the antiformant appears as a characteristic blank region, and in section patterns as a characteristic valley of the envelope. As we see in Fig. 8, higher modes of the antiresonance can also be found sometimes.

Thus, in short we could say, the antiformant plays the major r61e in identification of the point of articulation during the closure period of nasal consonants, whereas the common characteristic of nasals are

features (1) and (3) disregarding detailed variations of the structure of (3).

It shoud be noted, of course, that the characteristic time variation of the vocalic sound (i.e., the glide) between the consonants and the following or preceding vowel is usually more important in identification of stops and nasals? It should be remarked, however, that the sound structure of the stationary part of nasal consonants is essentially different from that of adjacent vowels. In the nasal, the sound is emitted from the nostrils and has a dull spectrum (with antiformants), which is quite different (or even just the converse sometimes as in cases of [-•] and [me] in Fig. 7) from the spectrum of the vowel characterized by the (oral) formants. This fact causes sometimes an essentially discontinuous transition in the structure of sound, or in other words, an abrupt change of timbre at the moment of release of the stop at the point of articulation, giving often an impression of "plosion," even when no actual plosive noise can be heard.

In Fig. 7, in the case of front tongue positions and [em], an antiformant in the region of 2000 cps-3000 cps (arrow) is replaced by the 2nd or the 3rd formant of the vowel, when the pipe is opened. In these cases, it is reasonable to assume that the formant is due to the

resonance of the front oral cavity, which at the same time gives the antiformant in the sound emitted from the nostrils.

9 Dr. Sinsak Horiguti early arrived at a similar conclusion on this point in his article, Japan. Z. Oto-Rhino-Laryngol. 49, 552-575 (1943).

10 Andr6 Ma16cot, Language 32, 274-284 (1956).

strongly [•i] weakly [•] [•] nasalized nasalized s.n. w.n. s.n. w.n.

FIG. 9. Sustained vowels (Japanese [z-I, [•-I, [•-I) pronounced with alterations of the degree of nasalization (Hattori).

It seems worth mentioning here that the antiformants also might have some connection with the distinctive features of laterals, fricatives, and stops possibly. We are planning to pursue this point in our further investigation.

6. DEGREES OF NASALIZATION AND THE NASAL

VOWELS IN FRENCH AND JAPANESE

6.1.

•he experiments described above were conducted in an attempt to clarify the characteristics of nasalization as the common features for five (Japanese) nasalized vowels. In the experiments we dealt chiefly with artificial pronunciations in which the degree of nasalization and the tongue articulation were kept as constant as possible. In actual speech, however, the degree of nasalization in the nasalized vowels is never uniform, and the articulation never static, all of which results in complicated phenomena. Also, in case of strong nasalization, it is possible that the vocal tract, viz., the pharyngo-oral channel is directly affected to an appreciable degree by the hanging velum. n

In order to study this point, Sonagrams were taken when the sustained vowels (five Japanese vowels) were repeated with alterations of the degree of nasalization (Fig. 9). It has been found that in cases of "a," "e," and "o," the absorption of characteristic (2) is lowered slightly when the nasalization is weakened. This can be due to narrowing of the back opening of the nasal cavity.

In the case of "a," it was also found that its third formant at about 2500 cps is much weakened when the vowel is heavily nasalized. This effect can be due to the muffling of the resonant sound of the laryngeal pharynx by the hanging velum. This effect is seen optimally for "a," the most open vowel, but the tendency can be found also in case of "o," as a flattening of the dull peak around ! 700 cps when the nasalization is increased. In the front vowel "i," the higher formants (2nd, 3rd, and 4th) are weakened without any shift of resonance, when the vowel is strongly nasalized. These formants may be attributed to the resonance of the front oral cavity (Sec. 5.2), and become weaker when the sound is emitted more from the nostrils than through the oral

np. Delattre reports that formant 3 rises considerably when the vowel gets nasalized, but this rise is not one of the changes responsible for nasal quality. Proc. Mod. Language Assoc. 66, 864-875 (1951).


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channel. In case of "e," the sound of the oral resonant cavity is not appreciably reduced, presumably because the oral channel is wider.

6.2.

Some phoneticians have observed that the nasalization of the French nasal vowels is extremely strong, e.g., O. Jespersen transcribes them with (/•3) in his antalphabetic notation. We have analyzed the pronunciation of Mr. Bernard Frank from Paris. The

nasalization of his nasal vowels is not uniform, however, and becomes heavier near the end of the sound, tending to or ending in nasals with the same point of articulation

(a)

(section)

as the following sound when the latter is a stop, and in

In [•-] of "un" and "vin, 'n" characteristic (2) appears not at the beginning but a little later, and disappears again in the last part. The sound before the following

•lb•is correspondingly obscure at the beginning. (2)is ending also found in [fi-] of "blanc," the sound in [•]. In

[ba:ko•], (1) appears almost all through the sound

whereas (2) starts a little later and is weakened as the nasalization becomes heavier. While the first and the

second formants of the vowel are maintained, the third formant disappears conspicuously midway through the vowel. The above experiment leads us to interpret this effect as being due to the hanging over of the velum.

6.3.

The sound sequence "vowel +/•/" in Japanese, resembles the French nasal vowels described above, although with some differences. When the Japanese /•/is followed by a stop, an affricate or a nasal, the preceding vowel is nasalized sooner or later and gradually glides into a nasal stop with the same point of articulation as the following consonant. The before vowels, semivowels, /s/ or /h/ is pronounced usually as a nasalized vowel.

In Fig. 11(a), we see the Sodagrams of [ba,] (evening) and [ba•3ku3/ba•ku/(bank) pronounced by Hattori in his native dialect (Kameyama). The latter

Fro. 10. French "un bon vin blanc" and "banque" pronounced by Mr. B. Frank (narrow band).

** Mr. Frank has only [•3 in place of ICe3 and

(b)

Fro. 11. Examples of Japanese/•/, pronounced by Hattori. (a) EbaN-] and Ebaroku-], (b) [pa;ja-] and [-pa•sa-].

resembles the Sodagrams of the French "banque" considerably, but a clear [•3-] appears before [k]. In the former example, [N-] at the end is retained considerably long (about 0.16 sec). Figure 11(b) shows Epaija] /paN'ja/ (bakery) and Epa•sa-]/paNsa/(It's bread, of course), which sometimes appears as [pa•asa-]. It is ascertained by the section patterns that the/•/in these cases are to be described as Ei] and [•], respectively.

7. ACKNOWLEDGMENTS

We owe very much to Professor Ichir6 Kirikae and Dr. Michiya Okamoto in the Otolaryngological Depart- ment of the University of Tokyo, for their kind coopera- tion and information upon which some of our experiments depended. We should like to express sincere thanks to Professor K6ji Sat6, Dr. Heiji Kawai, and Dr. Yutaka Kohasi, in the Kobayasi Institute of Physical Research, for their favors by which our cooperative study was made possible. We also express our deep gratitude to Professor Hidetosi Takahasi in the Department of Physics in the University of Tokyo for his valuable suggestions and remarks. We greatly appreciate •the kind and effective cooperations of Mr. Bernard Frank, Lecturer at the University of Tokyo and many of our colleagues and students. Finally, we are much obliged to Professor Morris Halle who kindly read through the manuscript and corrected our English expression in many places.


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Nasalization of Vowels in Relation to Nasals