Vowels in context

Vowels

In the production of vowel sounds, the articulators do not come very close together, and the pasage of the air stream is relatively unobstructed. Vowels cannot easily be described in terms of 'a place of articulation'. Instead, they are classified in terms of an abstract vowel space which is represented by the four-sided figure known as the 'Vowel Quadrilateral' (trapezium) or Vowel Chart. This space bears a relation, though not an exact one, to the position of the tongue in vowel production (Figure 6).

For the vowel labelled /i:/ in heed the body of the tongue is displaced forwards and upwards in the mouth, towards the hard palate. By taking it to the extreme position (after which the air becomes turbulent, resulting in a fricative) we can get the first reference point for vowel description. Since the tongue is near the roof of the mouth this vowel is described as close, and since the highest point of the tongue is at the front of the area where vowel articulations are possible, it is described as front.

Conversely, for the vowel labelled /a:/ as in father, the tongue body is displaced downwards and backwards, narrowing the pharynx. The most extreme version of this sound is taken as a second reference point. The space between the tongue and the roof of the mouth is as large as possible, so this vowel is described as open, and the tongue is near the back of the mouth, so it is described as back.

The positions of the tongue for /u:/, a close back vowel in doom, and for /ae/ in RP cat, a front open vowel, will also provide fixed references. By joining the circles representing the highest points of the tongue in the four references we can get the boundary of the space within which vowels can be produced. The vowel space can be stylized as the quadrilateral in which two fully front vowels /e/ and /e/ are defined by auditory impressions between /i:/ and /ae/, and two fully back vowels, /э:/ and /n/, are defined as the two steps between /u:/ and /a:/ (Figure 7).

As a result we will have four degrees of closeness-openness for English: high (close), mid-high, mid-low (mid-open), low (open) and three divisions along the front-back dimension: front, central, back. The amount of four vertical and three horizontal divisions is maximal for any language of the world. In Russian, for instance, there is only one low open vowel [a], so the vowel chart will look like a triangle (Figure 8):

The position of the lips varies considerably in different English vowels. They are generally closer together in the mid and high back vowels, as /u, u:, o:, t>, эи, аи/ in book, food, cord, cot, coat, cow. Vowels may be described as being rounded (with lip rounding) or unrounded (the lips are in the neu­tral position). In English lip rounding is not contrastive because no two vowels are contrasted in being rounded or unrounded without a change in quality which always comes first, but it is an indispensable feature of the vowels listed above.

The features we have looked at are the most important ones, but there are many other ways in which vowels differ from each other. Relatively slight movements of the tongue produce quite distinct auditory differences in vowel quality. If the quality of a vowel stays unchanged during its articulation, the term pure vowel, or monophthong, is used, as in red, car, sit, sat. If there is an evident change in quality, it is a gliding vowel. If two auditory elements are involved, the vowel is referred to as a diphthong, e.g. light, say, go; if three elements, as a triphthong, e.g. fire, hour (which tend to be monophthongs today).

Note: In American English historically long vowels and diphthongs are defined as one group of tense vowels, and the glides of diphthongs are not indicated in the symbols: /e/, for example, is a symbol of diphthong /ei/, /o/ is a symbol of the British diphthong /эо/, actually pronounced by Americans as [oo]. The reason for it is that long vowels and diphthongs have a lot in common: they are peripheral in the vowel space, and there­fore long and tense; long monophthongs are also diphthongized, at least /i:/ and /u:/ certainly are. Incidentally, these vowels are represented in American books as /i/ and /u/, with length unmarked. The facts show that classification depends on the framework of the school and the author.

Yet another way of classifying vowels is in terms of the amount of muscular tension required to produce them: vowels articulated in extreme positions are more tense than those articulated nearer the centre of the mouth, which are lax: cf. seat vs. sit, flute vs. foot.

There are also differences in vowel length, and some languages con­trast long and short vowels. British English, RP accent, for example, is claimed to have 20 vowels, usually divided into the following groups:

• short vowels: i, e, зе, л, d, и, з

• long vowels: i:, а:, з:, о:, и:

• diphthongs: ei, ai, or, au, эи, is, еэ, из

In English long vowels and diphthongs happen to be more peripheral sounds which require more tension and time for their articulation, and they also have specific vowel quality to identify them. Therefore, for the English language classification of vowels into long and short also means grouping them into tense and lax, while the identity of each particular vowel may rest on vowel quality alone. In other words, all long vowels and diphthongs are long and tense; short vowels are lax. There are no two vowels in English which are different in length or tenseness alone as there is always a distinctive vowel quality to identify each vowel. This accounts for the fact that vowel classifications in English are normally based on vowel quality alone.

The long/short, tense/lax categories of vowels are also distinguished from the point of view of energy discharge: short vowels are checked due to the accompanying glottal activity, involving a rapid energy discharge in a short time interval, while long vowels are unchecked (sometimes called free because of the fading nature of energy discharge), which applies to all non-glottalized sounds, signalled acoustically by a lower energy discharge over a large time interval.

To complete the list of possible vowel distinctions in different languages we can say that some languages have nasalized vowels in addition to normal (oral) ones; in these some of the air-flow is allowed to escape through the nose. French is a well-known example — the vowels in fin, bon, dans, brun are nasalized. Among other European languages, Portuguese and Polish also have nasalized vowels. In English nasalized vowels are pro­nounced under certain circumstances, before a nasal consonant, for example, in men but this quality change is allophonic, i.e. it does not change the meaning of a word (see Part II. Phonology).

In summary, vowels can be classified in terms of the following factors among which the first three are most important for English vowel quality:

• height of the body of the tongue (high, mid-high, mid-low, low)

• front-back position of the tongue (front, central, back)

• degree of lip rounding (rounded, unrounded)

• stability of articulation (monophthong, diphthong)

• duration (length) of the vowel segment (short, long)

• tenseness of the vocal organs (lax, tense)

• position of the soft palate (oral, nasal)

• energy discharge (checked, unchecked).

It should be noted here that, useful as it is for practical phonetics of teaching English, the description of vowels in terms of articulation is not quite accurate. Actually the two high vowels, /i:/ and /u:/ for example, are not equally high, /i:/ being much higher. Then there is the shape of the tongue and of the pharynx which affect the quality of vowels. We have to turn to acoustics to measure vowel sound properties more objectively.

It is important to note here how vowel features are affected by coarticulation with consonants and with other features of phonetic context. Length is especially susceptible to the following circumstances:

• vowels are longest in an open syllable, they are shorter in a syllable closed by a voiced consonant, and vowels are the shortest in a syllable closed by a voiceless consonant: cf. sea, seed, seat, sigh, side, sight; as a result, the so-called "short" vowel of Ш may be longer than the "long" vowel of beet;

• vowels are longer in stressed syllables than in unstressed ones: cf. bil­low, below— ['bitao], [bi'tau];

• vowels are longest in monosyllabic words, they are shorter in two-syllable words, and shortest in the words with more than two syllables: bid, bidder, forbidden, read, reader, readable;

• the vocal folds activity may be affected, thus producing a reduced voiceless vowel after a voiceless stop, as in the first syllables of the words potato, catastrophe;

• vowels may be nasalized before a nasal: man [maen];

• vowels are retracted before a word-final velarized /1/: bell, sill.

To sum up the features of vowel articulations which depend on coarticulation with the neighbouring consonants we can conclude that English vowels are normally affected by consonants which follow them. This rule concerns variation in length, nasalization and velarization. In American English it also concerns retroflexion of vowels before r.

The influence of the prosodic features of stress upon vowel length appears to be universal, common with many other languages of the world.

Vowel variants in particular phonetic contexts are discussed in Part II. Phonology.

1.3. Language acquisition: how speech sounds are learned

Intonation patterns are the first kind of linguistic structuring in the vocalizations of the child; they emerge as early as 6 months. Children appear to perceive intonational differences before differences in phonetic segments, discriminating intonational rise and fall contours in adult English speech by 8 months. In terms of production, by 8 months distinctive intonational contours of rise and fall can be detected in child's output. Though these early intonational patterns are not the same as fully-formed adult patterns, they may reflect their general characteristics and often signal differences in meaning. The acquisition of Chinese tone (4 distinct Mandarin tones) occurs well in advance of the mastery of segmentals, and within a short period of time. Just as tones are stored as part of the identity of the word in Mandarin, so also are stress patterns in languages like German, English, and Russian. For example, the stress difference between 'permit and permit is stored away as part of the underlying representation of these two words (Kess 1992:309-314).

Classifying consonants by the place of obstruction we proceed from the lips through the oral cavity to the larynx. Classifying by the manner of articulation we begin with the stops, then to fricatives and affricates. It was found that babies start practising sounds of their mother tongue when babbling in a similar order. There is a lot in common in sound acquisition among world languages. The order of acquisition of classes of sounds goes by manner of articulation: nasals are acquired first /m, n/, then stops /b, d, k/, liquids, fricatives and affricates. Classes characterized by place of articulation features also appear according to a certain order: (bi)labials, velars, alveolars and palatals.

The early babbles consist mainly of repeated consonant-vowel sequen­ces like mama, gaga, dada. Thus the first consonants are /b, m, d, k/, the first vowels are /a/ and /i/, the first syllables are of the consonant-vowel (CV) type, the basic rhythm is syllabic. (Even at a later stage American and English children stress form words and prepositions). The first meaningful contrasts are expressed intonationally: a high rise-fall of demand and a level (rise-fall-)rise of content.

All the children go through the stages of first babbling, then one-word period, then constructing sentences (telegraphic style). It is amazing that they do it so quickly: children do not seem to learn language, they "pick it up", and a five-year-old child can talk as well as an adult. A child can learn any language of the world he/she is exposed to. When and how do language-specific features occur?

At the age of 6 months the baby begins practising only the sounds which are contrastive (phonemic) in his own language. Thus, for instance, be­fore that age a Japanese baby can distinguish the sounds /1/ and /r/, but then he/she is unable to do that. The baby is a fine instrument attuned to the sounds of his mother tongue because he/she needs them to communi­cate, to distinguish meaningful units. Sounds which are more frequent in all the languages are acquired first.

It takes us to the problem of input. The critical period for language acquisition is from birth to puberty during which time a child must be exposed to human speech communication. The term for a type of child-directed speech is motherese, or baby-talk: adults tend to talk to babies in a special way by exaggerating pitch changes, labialization and palatalization. It is not the only source of language because the child can also hear adult-to-adult talk. Generally, as was found in experiments, the child's

perception goes ahead of production: he/she can distinguish the sounds but fail to pronounce them properly.

It was found that the child is learning sounds to discriminate meaningful units, words and their grammatical forms. In English, for instance, the syntactic competence of a two-year-old child involves a patterned word order: subject — verb — object (SVO), while for a Russian child the morphology of words is more important, and the endings appear first, at the age of two.

Bilinguals are reported to create two vocabularies and two grammars simultaneously. They have an intermediate stage of cognate development when they can use the resource of one language for the other language usage. There are no generalizations about the phonetic discrimination of the two languages. Many bilinguals acquire the speaking fluency in both languages.

In second language learning there seems to be also the critical age after which the pronunciation of the target language is difficult to acquire. Every year counts and seems to diminish the chances of success. It should be noted, however, that unlike learning one's mother tongue, which in most cases is a creative but an unconscious process, second-language acquisition is both creative and conscious. A child or an adult is shown contrastive patterns of sounds, words and syntactical patterns, and a lot of things are explained. Motivation and practice are the necessary ingredients of success.

Just like imitation, analogy and reinforcement are not the only ways to learn the mother tongue, so are good models, drills and language environment not the only ways of learning a foreign language pronunciation. It takes a conscious effort to discriminate the automatic speaking habits of the mother tongue from those of the target language. Mastering them in mature age is quite a difficult task even for the persons placed in favourable language surroundings.

1.4. Acoustics: how speech sounds are processed and described

Speech technologies is such a fast developing area of applied phonetics that we cannot predict what the facilities for speech processing will be like tomorrow. Whatever we write may be outdated very quickly. Our task, therefore, is to take a look at the principal ways speech can be observed and analyzed.

In the phonetic laboratory we analyze speech using computers. The acoustic properties of sound signal are easier to observe than the exact positions of the tongue: we can record the signal and measure it thanks to the computer programs which are designed to process it. For each of the phonetic classes of sound that we have identified we can find corresponding acoustic patterns.

When talking, we produce sound waves which travel in the air and reach the eardrum of the listener. This acoustic signal can be recorded and processed with the help of a computer program, then observed as a waveform on display. We can see acoustic patterns corresponding to each class of sounds.

Vowels, for instance, are periodic sounds: they have a regular pattern of vibration repeating its pattern over and over. Fricatives like /f, s, \/ are aperiodic sounds having an irregular, messy pattern. Voiceless stops (plosives) start with silence (at the complete closure of the mouth) which we see as absence of signal, a gap. When the closure is released there is an aperiodic sound, like a brief fricative. If/p, t, k/ are aspirated, the aperiodic sound is like [h]. Voiced stops (plosives) are periodic during the time the vocal tract is closed but the English /b, d, g/ actually have very little voicing (see Figure 9).

We can measure the time taken by each particular sound on the horizontal axis. The parameter is called duration. The frequency of vibration and the amplitude (the amount of energy contained in the sound) can be taken in the acoustic spectral analysis. The underlying principle is that the complex waveform of a sound can be broken down into simple waveforms of different frequencies (like breaking down white light into rainbow pattern of colours), and we can measure the energy at each frequency. In the picture which is called spectrogram they look like dark bands and are called formants. Darker bands represent greater energy. The vertical axis represents the frequency scale, the horizontal axis shows the time. Thus we can see how energy is distributed at different frequencies at any stage of the sound production.

In vowels the energy is concentrated in three or four narrow bands (formants) in the lower part of the spectrum. The formant with the lowest frequency, Formant 1 (F_t) corresponds roughly to the traditional open/close dimension: a low F, corresponds to a close vowel, like ft/ or /ul/. dormant 2 (F₂), which is higher than F_t corresponds roughly to the front/back dimension of vowels: a vowel with a high F₂ is likely to be a front vowel like /e/ or /a/. A low F₂ is more likely to be a back vowel like /t>/, /a:/.

Frequency values vary from speaker to speaker but, nevertheless, there are group means (averaged data) for BBC female newscasters, for example, against which the speech of Queen Elizabeth II was compared to find Her Majesty's progress towards a more democratic national standard pronunciation of vowels.

Prosody (or intonation), among the suprasegmental (spreading over a number of segments) features can also be analyzed acoustically. The parameters are: fundamental frequency (F^, intensity (Int), duration (T), which correspond to the perceptual categories of pitch, loudness, length.

Fundamental frequency curves show where the voice goes up (rise) or down (fall). A change in fundamental frequency may serve to distinguish the meaning of words in tone languages or the meaning of sentences in intonation languages (see Figure 10). It is also one of the major components of accent (stress) in English and Russian.

The duration of segments, syllables, intonation units and pauses may demonstrate the tempo and rhythm of speech. Duration is also a powerful means of stress in Russian and a few dialects of English where speech is monotone, such as conversational American English or Irish English, for instance.

Intensity level and change may demonstrate the way speakers employ loudness change: British English speakers keep up a high level of intensity while Russian speakers keep changing it: the fact suggests that loudness variation is more important for accent in Russian, while pitch change is, no doubt, the major accentual means in English.

An important side of acoustic phonetics is speech synthesis. Although scientists are still dissatisfied with the quality of synthesized speech, it is a very useful tool to learn more about a person's reactions to various modifications of sounds and their properties. Acoustic phonetics is also used in health service, in security systems and for communication and other technical purposes in aviation and the navy, for instance.

There are phonetic laboratories which employ other instrumental techniques, such as palatography and ultrasonic equipment; even X-ray methods used to be practised to find the exact location of articulators in the process of speaking. The minimal equipment which we need today will consist of the tape-recorder and the computer.

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