8 Classification and Description of Speech Sounds: English Vowels
Dr. Neeru Tandon
Learning Outcome:
This chapter Classification and Description of Speech Sounds: English Vowels will tell you about the key components of linguistics and classification of speech sounds, especially vowels. In a nutshell it will make you comfortable with key concepts of pronunciation of English words.
- Vowel Sounds
- How to Pronounce Vowel Sounds
- Tips to improve pronunciation
Introduction
Verbal communication involves turning our non- linguistic experiences (thoughts, feelings, ideas, wishes, wants, and so on) into language and then communicating the subsequent linguistic units (words) through some suitable medium. Other people are then capable to decode the words and, thereby, convert the sense of what we were intending to communicate. There are three main modes that we transfer linguistically encoded messages:
- Speaking
- Writing
- Signing
It is evident that all typically developing people learn to speak: speech acquisition is a natural process. However, not all people learn to read and write. Literacy skills have to be taught: they are not the product of a natural process. In this sense, speech is prior to writing as a transmission system. In fact, speech is the primary medium through which people communicate using language.
VOWELS: We know that tightening the airstream to several degrees produces consonants, as it flows through the oral tract. Vowels are distinguished from consonants in numerous ways. Vowels are twisted with a smooth, unhindered airflow through the oral tract. A provisional rule of thumb is that vowels consist of the sounds represented by the letters a, e, o, u, y and sometimes I.
Gimson defines vowels (2) as a “category of sounds … normally made with a voiced egressive air-stream, without any closure or narrowing such as would result in the noise component characteristic of many consonantal sounds” (Introduction 35).
He gave a list of several correlates in speech sound classification (Speech pp. 153-155). What follows is a compiled overview of properties a sound should have, according to Fant, to be classified as a vowel. The first condition is that a vowel must have sound energy visible in sound spectrum, and that the source of the acoustic energy originates from the vocal folds vibration. A vowel should also have “vowelike correlate” in speech production, which means an unobstructed pass of airstream. Waveform analysis of a “vowelike sound” implies that “at last F1 and F2 [are] detectable”, while F3 should be visible if F1/F2 are not at their lower ends (156). To classify a vowel as a diphthong, the speech sound must satisfy the “glide” correlate, which in the production context means “moderate speed within a segment”, seen as a “relatively slow [spectrum change] rate but faster than for mere combination of two vowels”.
Gimson refers to vowels in the introductory chapters as “the vowel type” of sounds, “described in mainly auditory terms” (Introduction, 35). When discussing the vowel versus the consonant distinction he notes: “It will be found that the phonemes of a language usually fall into two classes, those which a typically central (or nuclear) in the syllable and those which are non-central (or marginal). The term ‘vowel’ can then be applied to those phonemes having the former function and ‘consonant’ to those having the latter.”
Distinctive shapes of the oral cavity create differences in vowel quality. In fact production of vowel sounds arises without impediment or thinning in vocal tract. ‘A sound due to an audible friction without obstruction & narrowing of a degree in the pharynx and the mouth is known as Vowel Sound.’ Sounds produced due to articulators like nose, upper lip, lower lip, pharynx, tongue and other vowel sounds can be differentiated due to length of different vowel sounds for example hit & heat. Hit is pronounced with short vowel sound and heat is pronounced with long vowel sound.
CHARACTERISTIC VOWEL QUALITIES: According to Delahunty, Gerald P Characteristic vowel qualities are determined by
- (a) the height of the tongue in the mouth;
- (b) the part of the tongue raised (front, middle, or back);
- (c) the configuration of the lips; and
- (d) the tension of the muscles of the oral tract. An articulatory description of a vowel must include all of these features.
- Openness of the mouth
- Tongue elevation
- Position of tongue elevation
- Lip shape
- Length of vocalization
The first four of these alter the relative size and shape of the oral cavity. The final parameter (length of vocalization) influences the duration of production.’’
OPENNESS OF THE MOUTH
Vowels differ from one another according to the extent to which the jaws are either open or close (not ‘closed’, as a complete closure would prevent the free flow of air out of the mouth). When, you speak the vowel sound /ɑ/, as in the word palm, the jaws are wide apart and you have embraced a comparatively open mouth posture. This is, therefore, an open vowel. Now contrast this with the vowel /i/, as in the word fleece. This time, you should notice that the mouth is nearly closed, i.e. the vowel /i/ is a close vowel. You can both see and feel the relative openness or closeness of the mouth by alternating the production of these vowels in quick succession (/i/ – /ɑ/ – /i/ – /ɑ/ – /i/ – /ɑ/).
To facilitate the description of vowels, a finer grading system is used to define the extent to which the mouth is either close or open. The categories are:
- Close: the mouth is nearly closed, as we have seen with the vowel /i/
- Close mid: this position is intermediate between a middle position (in which the mouth is open almost exactly halfway) and the close position.
- Open: the mouth is wide open, as with the vowel /ɑ/
- Open-mid: this position is intermediate between a middle position (in which the mouth is open almost exactly halfway) and the open position.
TONGUE ELEVATION
When articulating vowels, there is a correlation between tongue elevation and openness of the mouth. Close vowels (with the mouth relatively closed) are articulated with a relatively high tongue elevation. In contrast, open vowels are typically articulated with a relatively low tongue position. As you will probably have guessed, close-mid and open-mid vowels are generally articulated with the tongue elevation in a mid-position, intermediate between high and low.
Pronounce the words eat and at. Now pronounce just the vowels of these two words. Notice that as you go from the vowel of eat to the vowel of at, your mouth opens. Alternate the words, and then just the two vowels.
Once you’ve become accustomed to the different degrees of openness of these two vowels, pronounce ate between eat and at. The degree of open- ness of its vowel falls between those of eat and at, so there is a continuous increase in mouth openness as you go from one vowel to another. These degrees distinguish high, mid, and low vowels. We will use the following symbols for this sequence of vowels:
- Eat [i] High
- ate [e] Mid
The tongue can take up a variability of positions in the mouth. On the vertical axis it is usually explained as taking up one of three locations. Suppose the tongue takes a high position and it is the vowel sound /i/ as in the word fleece (which we know is also a close vowel). Try saying /i/ aloud again whilst looking in a mirror. This time, instead of concentrating on the position of the jaws, see and feel that the front portion of the tongue is raised relatively high in the mouth. Now contrast this with the vowel /æ/ as in the word trap. In it the tongue takes up a low point in the mouth. An example of a vowel in which the tongue is placed about halfway between high and low is the sound /ɛ/ as in the word press. This is, therefore, described as a mid-vowel.
POSITION OF TONGUE ELEVATION
Elevation of tongue is closely related with position of tongue elevation. Whereas the elevation of the tongue describes the position of the tongue on the vertical axis (high, mid, low), the ‘position of tongue elevation’ refers to where this elevation takes place on the horizontal axis. Again, three positions are recognized:
- Front
- Central
- Back
Front Vowel: Referring once more to the vowel /i/, we have noted that it is both a close vowel and a high vowel. In it the elevation of the tongue is at the front of the mouth. It is, therefore, also described as a front vowel. This is because the highest point of the tongue is towards the front of the mouth, below the front portion of the hard palate.
Front vowels are produced with the front part of the tongue raised towards the hard palate. There are four front vowels and they are largely the same for speakers of both American and British English.
The font vowels are distributed in the vowel space almost equidistantly along the vertical tongue height axis (from high to low). They are all made with unrounded lips.
The vowel /i/ (as in the word heed) is the vowel made with the highest tongue elevation – it is the close vowel. Since it is made with tongue elevation at the front of the mouth, and is unrounded, it can be lab’eled simply as the HIGH FRONT UNROUNDED vowel.
According to author Graham Williamson, ‘ It is a long vowel and so it may also be transcribed as /iː/.The second vowel /ɪ/ (as in the word hid) is made with the tongue lowered slightly in the mouth, but not quite to the mid position: it is nearer the mid-high position. It is, therefore, a mid-high vowel. In addition, the vowel is made slightly further towards the central part of the mouth. Having said this, it is fairly close to the front and, as such, it can be referred to as a fairly-front vowel. This lowered and centralized unrounded vowel can, therefore, be described as the mid-high, fairly-front unrounded vowel. Or, given that the dimensions in the idealized vowel space are not intended to be represented with great precision, we can simplify the description and label it as the MID-HIGH FRONT UNROUNDED vowel. It is a short vowel. The third vowel is /ɛ/ (as in head). This is the MID-LOW FRONT UNROUNDED vowel. It is also a short vowel.’
The fourth type of vowel is /æ/ (as in bad). Though it is not quite fully open, still being articulated in an intermediary position between low and mid-low, it does have the lowest tongue elevation of all the front vowels. Subsequently, we can indicate to it as LOW FRONT UNROUNDED vowel. Like /ɪ/ and /ɛ/, the low front unrounded vowel is also short.
Central Vowel: Now contrast this again with the vowel /ɑ/, as in the word palm. This time, as you say the vowel aloud, you should sense that the tongue elevation is towards the back of the mouth. This is, therefore, a back vowel sound, i.e. the highest point of tongue elevation is towards the back of the mouth, below the soft palate. The central position is harder to both see and feel but an example of this is the vowel /ɜ/ as in the Southern British English pronunciation of the word curse. Central vowels are, logically, articulated with the highest point of the tongue intermediate between the front of the mouth (below the front portion of the hard palate) and the back of the mouth (below the soft palate).
All central vowels are produced in an intermediate position between front and back vowels, with the body of the tongue raised towards the roof of the mouth in the area where the hard and soft palates fuse.
British central vowels
Figure 9 illustrates the central vowels typically used by speakers of Standard Southern British English (SSBE).
We see from Figure 9 that speakers of SSBE have two vowels produced with the tongue elevated to the mid position. One is short and unrounded and the other is long and rounded.
The vowel /ɜ/ (as in urban) is the long rounded vowel. Being long it may on occasion be transcribed as /ɜː/. It is the MID CENTRAL ROUNDED vowel. This vowel only occurs in stressed syllables. A stressed syllable is a syllable in a multisyllabic word that is given more emphasis than the other syllables when spoken. The speaker raising the pitch of the sounds that constitute the syllable often achieves the extra prominence. Primary stress is usually signified with a superscript mark (ˈ) before the affected syllable. In contrast, some syllables in multisyllabic words receive no stress at all. They are spoken with no extra prominence: no extra respiratory energy is used to give them prominence. These are unstressed syllables. For example, in the word photograph the second syllable ‘-to’ is unstressed.
Again I will like to quote Graham Williamson. According to him, ‘The vowel /ə/ (as in annoy) is the counterpart vowel to /ɜ/, being unrounded and short. It is, therefore, the MID CENTRAL UNROUNDED vowel. It is often known by its German name schwa or, simply, as the neutral vowel. This is because, in contrast with /ɜ/, the neutral vowel most commonly occurs in unstressed syllables, either in syllable-initial position (e.g. around) or syllable-final position (e.g. soda).A third central vowel is available to speakers of SSBE, /ʌ/ (as in hut). It is formed with unrounded lips and it is short. It is the LOW CENTRAL UNROUNDED vowel.’
American central vowels
Speakers of General American English (GA) use two of the central vowels that are also used by SSBE speakers: the MID CENTRAL UNROUNDED neutral vowel /ə/ (as in ahoy) and the LOW CENTRAL UNROUNDED vowel /ʌ/ (as in bud) (see Figure ).
Unlike SSBE, however, GA does not make use of the mid central rounded vowel /ɜ/ in quite the same fashion. In General American, this mid central rounded vowel is said to be r- colored. In American English it is typical for vowels preceding an /r/ to be affected by the immediately following consonant such that the tongue is curled back slightly during production of the vowel. This is known as retroflexion. So, in GA, the mid central rounded vowel in the word bird is r-colored, owing to the effect of the immediately following /r/ consonant. The vowel may be transcribed with a small ‘r’ symbol attached /ɝ/ or with a following ‘r’ /ɜr/ (see Figure 10).
Back Vowel: The back vowels, like the front ones, descend from high, through mid, to low, in a continuous sequence. You can observe this by pronouncing the words coot, coat, and cot, and then just their vowels. As you produce this series of vowels you’ll find your mouth opening (monitor your lower jaw) as you go from coot to coat to cot. We use the following symbols for these back vowels: (2) coot [u] High coat [o] Mid cot [A] Low
LIP SHAPE
During the production of English vowels, just two lip shapes are usually adopted:
- Rounded
- Unrounded
The difference can be illustrated by alternating between saying the vowel sounds /u/, as in the word Loose and /i/, as in the word fleece. Look at yourself once more in a mirror as you alternate between saying these vowels in rapid succession (/u/ – /i/ – /u/ – /i/ – /u/ – /i/). You will see that the lips are rounded and pushed forwards for the production of /u/ but that they are spread (unrounded) for the vowel /i/.
As you compared [i] and [u] you probably noticed that your lips changed shape as you shifted from the front vowel to the back one. Your lips were rounded as you produced [u]. They were unrounded (spread or neutral) as you produced [i]. As you moved through the series of back vowels you may also have noticed that lip rounding decreased as you moved from high to low. In fact the lips are unrounded during the pronunciation of [A]. In English, the only rounded vowels are back, though many languages, such as French and German, have rounded front vowels.
INTERMEDIATE VOWELS
First, pronounce the words meat, mitt, mate, met, and mat. Then pronounce just their vowels:
The vowels we’ve just added, [I] and [E], are intermediate in height between [i] and [e], and
Vowels in multi-syllabic words Pronounce the words above, soda, sofa, comma, arena, patina, photograph, paying particular attention to the vowel represented by the bold letters. Then pronounce this vowel in isolation. This vowel is called schwa and written [@]. Schwa is made at approximately the same place as [V], that is, farther forward than the back vowels and farther back than the front ones. Hence, it is central. In addition, [@] is mid, lax, and unrounded. It is heard primarily in unstressed syllables, as in the words above. It is the vowel we produce if we vocalize as we prepare to speak—uh. The tongue is said to be in its neutral position as we pronounce this vowel.
LENGTH OF VOCALIZATION
Without exception, vowels are produced with the vocal folds vibrating. They are, therefore, all voiced. In addition, vowels may be sustained for relatively longer and shorter intervals of time. They are categorized as: long and short. Again, saying the vowel sound /u/, as in the word goose. This can be heard to be a relatively long vowel if you now contrast this by saying the vowel /æ/ as in trap.
A further example of a long vowel is /i/, as in peat. This can be contrasted with the short vowel /ɪ/, as in pit. Again, try speaking aloud these two words, alternating between them,
i.e. peat – pit – peat – pit, and so on. This should help you distinguish the relative difference in the length of vocalization of /i/ and /ɪ/. Sometimes, for example when it is important to make clear that a particular vowel is a long vowel, a colon-like mark (ː) is placed after the symbol for the vowel, e.g. /iː/, /uː/, /ɑː/.
There are other parameters that could be invoked in order to provide a complete description of vowel sounds, e.g. whether or not the tongue is flat during vowel production or whether it is curled upwards and backwards (known as retroflex). For most purposes, however, the five parameters described above do.
DIPHTHONGS
The vowel sounds in the words boy, by, and how involves a change in the shape of the mouth as the vowel is being produced. The vowel of toy begins with approximately the mid back vowel [O] and finishes with ap- proximately the high front lax vowel [I] (or the palatal glide [j]). The vowel of by begins with approximately the low back vowel [a] (a low back vowel slightly more f approximately [I] (or [j]). The vowel of cow begins with approximately [a] and finishes with approximately the high lax rounded vowel [U] (or the labio-velar glide [w]). We represent these diphthongs as [OI], [aI], and [aU], respectively (though many linguists use [Oj], [aj], and [aw]).
A second set of English diphthongs is not as clearly notable as the first, chiefly because we tend to observe them as simple vowels. However, in a precise (narrow) phonetic transcription they must be characterized as diphthongs. The tense front vowel [e] is diphthongized. The vowel of boat is actually pronounced [oU]. So, the front tense vowel is diphthongized by the addition of a front vowel and the back tense vowel is diphthongized by the addition of a back vowel. We can express this pattern as a rule: Mid and high tense vowels are diphthongized by the addition of a high lax vowel that matches the original vowel in front or back.
Diphthongization of these vowels is a feature of English rather than a universal feature of natural language. Spanish and German language, do not diphthongize their corresponding vowels. The tendency to diphthongize these vowels is one characteristic of the “foreign accent” that betrays English speakers when they begin to learn these languages.
The first of these is the vowel /ɪə/ as it appears in British pronunciations of the word near. From the IPA symbol used to represent this vowel, it can be seen that the vowel begins with an articulation of the mid-high front unrounded vowel /ɪ/ followed by a smooth transition towards the vowel /ə/.
The second diphthong begins with the mid-low front unrounded vowel /ɛ/ before moving towards /ə/. The diphthong created by this rapid and smooth movement is, therefore, transcribed as /ɛə/. This is the vowel sound that occurs in the word square.
The third, and final, diphthong in this group begins with the mid-high back rounded vowel /ʊ/. The resultant diphthong is transcribed as /ʊə/. It occurs in British pronunciations of cure.
Standard Lexical Sets introduced by the linguist John C. Wells in 1982
It is useful to consider the pronunciation of vowel sounds in English through the idea of Standard Lexical Sets, introduced by the linguist John C. Wells in 1982. Wells defined one lexical set on the basis of the pronunciation of words in the reference accent Received Pronunciation (RP) for the English spoken in England. English has five vowels in its alphabet: a, e, i ,o u. However, there are many more ways of pronouncing the vowels than the five sounds given by a,e,i,o,u. /a/ can be pronounced as a ‘short’ sound as in the word <bad>, or pronunciations common in the North of England, such as <grass> and <bath>. It can also represent a ‘long’ sound, as in the word <laugh>, or <bath>, and <grass>. The sound represented by /o/ can also be spelt in different ways, such as in the word <off> or in <cough>.
STANDARD VOWEL CHART
Anatomically, there is more space towards the roof of the mouth than the floor. If the tongue is raised higher than the top axis this narrows the gap between the tongue and palate to such an extent that the outgoing airflow becomes turbulent and friction is created, i.e. a fricative consonant is produced. Similarly, if the tongue is lowered (or backed) below the position of the /ɑː/ vowel, friction is also created. The sloping left edge of the quadrilateral corresponds to the palatal area of the oral cavity and the straight right edge corresponds to the velar area. Consequently, the left edge represents front vowels and the right edge represents back vowels. Finally, the vowel quadrilateral is typically divided into six areas by a sloping central axis that cuts through the close, close mid, open-mid and open axes. As we will see, these divisions provide a useful means of describing vowels.
We do not need to be explicit about openness of the mouth because, as we have seen, it correlates with tongue elevation. It would, therefore, be redundant on any chart. Since a so- called vowel chart is concerned with plotting the relative positions of where vowels are made in the mouth, it is also not necessary to explicitly indicate the length of vocalization. The chart uses the quadrilateral to represent, in stylized form, the shape of the mouth based on a vertical axis of height of tongue elevation and a horizontal axis of the position of the tongue elevation.
MONOPHTHONGS/PURE VOWELS/SIMPLE VOWELS: When a speaker assumes only a single configuration of the mouth when producing a vowel, i.e. there is no movement of the tongue, lips or jaws, the speaker produces what is known as a simple vowel. In sum, once the appropriate position for the tongue, jaws and lips has been set, this configuration does not alter whilst the sound is being produced. Owing to this single configuration, simple vowels are often referred to as monophthongs. They are also sometimes known as pure vowels. However, we will use the term ‘simple vowel’ to describe this subset of vowels.
There are 12 simple vowels found in General American (GA) and Standard Southern British English (SSBE) in relation to each position of tongue elevation:
Complex Vowels :Simple vowels do not change the configuration of the oral cavity whilst the vowel is being produced. There are, however, some vowels that do entail changes to the configuration of the oral cavity during their production. These are known as complex vowels. An example is /ɔɪ/ as in boy. Try saying this aloud whilst looking in a mirror. You should notice that your mouth shape changes as you produce the vowel, demonstrating the dynamic reconfigurations that typify complex vowels.
Complex vowels that involve two broad configurations of the mouth during their production (a starting configuration and an ending configuration) are known as diphthongs. These can be thought of as being created through the combination of two simple vowels.
Back Vowels
The largest group of simple vowels is the back vowels. These are shaped with the back of the tongue raised towards the soft palate (velum). There are six back vowels, compared to the four front vowels and two central vowels.
Four of the back vowels are made with rounded lips and just one with unrounded lips. We see, therefore, that back vowels are generally produced with rounded lips (in contrast with front vowels, that are all produced with unrounded lips). Further, two of the back vowels are produced with a high elevation of the tongue, one with a mid-elevation, and two with a low elevation.
The first of the high vowels is /u/ (as in food). It is made with rounded lips and it is known as the HIGH BACK ROUNDED vowel. It is a long vowel and so may be transcribed as /uː/.
The second high vowel is /ʊ/ as in good. It is similarly made with rounded lips. However, it is also articulated with a somewhat lowered tongue elevation, close to the mid-high position. In addition, it is articulated slightly further towards the central position of the mouth than the /u/ vowel. It is, however, fairly near to the back and so it is a fairly back vowel. This lowered and centralized high back vowel may, consequently, be referred to as the mid-high, fairly- back rounded vowel. This is a short vowel.
The vowel made with mid tongue elevation is /ɔ/ (as in hawed). Being unrounded, it may be labeled as the MID BACK ROUNDED vowel. Speakers of General American English (GA) may produce the /ɔ/ vowel with a slightly more lowered and slightly more centralized tongue position than the vowel as used by speakers of Standard Southern British English (SSBE). Nevertheless, they are sufficiently similar to both be described as a mid-back rounded vowel. They are long vowel sounds and so may be transcribed as /ɔː/.
The final two back vowels are both made with a relatively low tongue elevation.
The vowel with the lowest tongue elevation is /ɑ/ (as in American and British pronunciations of the word palm). This is a fully open vowel sound and it is produced with unrounded lips. It is, therefore, the LOW BACK UNROUNDED vowel. It is a long vowel and, as such, may also be transcribed as /ɑː/.
The final vowel is produced with slightly higher tongue elevation and slightly retracted tongue position. It is the sound /ɒ/, as in SSBE pronunciations of the words cot, pot and lot. Being very nearly articulated in the same position as /ɑ/, it is also described as a low back vowel. However, it differs from /ɑ/ in that it is short and articulated with rounded lips. We can, therefore, describe it as the LOW BACK ROUNDED vowel. This vowel does not appear in General American English. GA typically uses /ɑ/ where SSBE uses /ɒ/. So, whereas SSBE distinguishes between the vowels in palm /pɑm/ and lot /lɒt/, GA does not – realizing both palm /pɑm/ and lot /lɑt/ with the same /ɑ/ vowel.
SUMMARY: Phonetics has been defined as the science of speech sounds. It is a branch of linguistics and deals with the sounds produced by human beings in their speech behaviour. Speech Sounds are divided into two main groups: (1) consonants, and (2) vowels. In order to describe the vowels, we usually draw three points in the horizontal-axes: front, central and back, referring to the part of the tongue which is the highest. So we have
i) front vowels,
ii) back vowels, and
iii) central
All English vowels are voiced. To depict the vowel sound we must indicate whether it is open or close, half-close or half-open, front or back or central, long or short, whether the tongue is tense or relax while the vowel is being pronounced, and whether lips are spread, neutral, open rounded, or close rounded.
From the point of view of their quality, vowel sounds are of two types: monophthong and diphthong. Monophthongs are pure vowels and diphthongs are gliding vowels. ‘A vowel that does not change in quality’ may be called a monophthong; and a vowel sound with a continually changing quality may be called a diphthong.
To quote Ladefoged, P. and Johnson
‘’In summary, the targets for vowel gestures can be described in terms of three factors: (1) the height of the body of the tongue; (2) the front–back position of the tongue; and (3) the degree of lip rounding. — It is very difficult to become aware of the position of the tongue in vowels, but you can probably get some impression of tongue height by observing the position of your jaw while saying just the vowels in the four words heed, hid, head, had. You should also be able to feel the difference.’’)
To conclude in the words of –Peter MacCarthy (English Pronunciation) ‘’A pure vowel is one for which the organs of speech remain in a given position for an appreciable period of time. A diphthong is a vowel sound consisting of a deliberate, i.e. intentional glide, the organs of speech starting in the position of one vowel and immediately moving in the direction of another vowel. A diphthong, moreover, consists of a single syllabic––that is, the vowel-glide most be performed with a single impulse of the breath; if there is more than one impulse of breath, the ear perceives two separate syllables…’’
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References
- Aoyama, K., Flege, J. E., Guion, S. G., Akahane-Yamada, R., and Yamada, T. (2004). Perceived phonetic dissimilarity and L2 speech learning: the case of Japanese /r/ and English /l/ and /r/. Journal of Phonetics 32: 233–50.
- Avery, P. and Ehrlich, S. (1992). Teaching American English Pronunciation. Oxford: Oxford University Press.
- Ball, M. and Lowry, O. (2001). Methods in Clinical Phonetics. London: Whurr.
- Celce-Murcia, Marianne, D.M. Brinton, and J.M. Goodwin. 1996. Teaching Pronunciation: A Reference for Teachers of English to Speakers of Other Languages. Cambridge, UK: Cambridge University Press.
- Crane, B.L., E. Yeager, and R.L. Whitman. 1993. Phonetics. In L.M. Cleary and M.D. Linn (eds.). Linguistics for Teachers. pp. 397-410. New York: McGraw Hill.
- McMahon, April. 2001.An Introduction to English Phonology. Oxford, UK: Oxford University Press.
- Pennington, Martha C. 1996. Phonology in English Language Teaching. Phonetics and Phonology London, UK: Longman.
- Yavaş, Mehmet. 2006. Applied English Phonology. Oxford, UK: Blackwell.