Thursday, August 23, 2012

Articulatory Phonetics: The Vocal Organs

Phonetics is concerned with describing the speech sounds that occur in the languages of the world. We want to know what these sounds are, how they fall into patterns, and how they change in different circumstances. Most importantly, we want to know what aspects of the sounds are necessary for conveying the meaning of what is being said. The first job of a phonetician is therefore trying to find out what people are doing when they are talking and when they are listening to speech.
The Vocal Organs
We will begin by describing how speech sounds are made. In nearly all speech sounds the basic source of power is the respiratory system pushing air out of the lungs. Try to talk while breathing in instead of out. You will find that you can do it, but it is much more inefficient than superimposing speech on an outgoing breath.
Air from the lungs goes up the windpipe (the trachea, to use the more technical term; and into the larynx, at which point it must pass between two small muscular folds called the vocal cords. If the vocal cords are apart, as they normally are when breathing out, the air from the lungs will have a relatively free passage into the pharynx and the mouth. But if the vocal cords are adjusted so that there is only a narrow passage between them, the pressure of the airstream will cause them to vibrate. Sounds produced when the vocal cords are vibrating are said to be voiced, as opposed to those in which the vocal cords are apart, which are said to be voiceless.
In order to hear the difference between a voiced and a voiceless sound, try saying a long v sound, which we will symbolize as [vvvvv]. Now compare this with a long f sound [fffff], saying each of them alternately—[fffffvvvvfffff vvvvv). Both of these sounds are formed in the same way in the mouth. The difference between them is that [v] is voiced but [f] is voiceless. You can feel the vocal cord vibrations in [v] if you put your fingertips against your larynx. You can also hear the buzzing of the vibrations in [v] more easily if you stop up your ears while contrasting [fffffvvvvv].
The difference between voiced and voiceless sounds is important in all known languages. In each of the pairs of words "fat, vat; thigh, thy; Sue, zoo" the consonant in the first world of each pair is voiceless, whereas that in the second word is voiced. Check this for yourself by saying just the consonants at the beginning of each of these words and trying to feel and hear the voicing as suggested above. Try to find other pairs of words that are distinguished by one having a voiced and the other having a voiceless consonant.
The air passages above the larynx are known as the vocal tract. Figure 1.1 shows their location within the head. The shape of the vocal tract is a very important factor in the production of speech, and we will often refer to a diagram of the kind that has been superimposed on the photograph in Figure 1.1. Learn to draw the vocal tract by tracing the diagram in this figure. Note that the air passages that make up the vocal tract may be divided into the oral tract within the mouth and the pharynx, and the nasal tract within the nose. The upper limit of the nasal tract has been marked with a dotted line since the exact boundaries of the air passages within the nose depend on soft tissues of variable size.
The parts of the oral tract that can be used to form sounds are called articulators. The articulators that form the lower surface of the oral tract often move toward those that form the upper surface. Try saying the word “capital” and note the major movements of your tongue and lips. You will find that the back of the tongue makes contact with the roof of the mouth for the first sound, and then comes down for the following vowel. The lips come together in the formation of p and then come apart again in the vowel. The tongue tip comes up for the t and again, for some people, for the final l.
The names for the principal parts of the upper surface of the vocal tract are given in Figure 1.2. The upper lip and the upper teeth (notably the frontal incisors) are familiar enough structures. Just behind the upper teeth there is a small protuberance that you can feel with the tip of the tongue. This is called the alveolar ridge. You can also feel that, the front part of the roof of the mouth is formed by a bony structure. This is the hard palate. You will probably have to use a finger tip to feel further back. Most people cannot curl the tongue up far enough to touch the soft palate, or velum, at the back of the mouth. The soft palate is a muscular flap that can be raised to press against the back wall of the pharynx and shut off the nasal tract, preventing air from going out through the nose. In this case there is said to be a velic closure. This action separates the nasal tract from the oral tract so that the air can go out only through the mouth. At the lower end of the soft palate there is a small appendage hanging down that is known as the uvula. The part of the vocal tract between the uvula and the larynx is the pharynx. The back wall of the pharynx may be considered to be one of the articulators on the upper surface of the vocal tract
Figure 1.3 shows the lower lip and the specific names for different parts of the tongue which form the lower surface of the vocal tract The tip and blade of the tongue are the most mobile parts. Behind the blade is what is technically called the front of the tongue: it is actually the forward part of the body of the tongue, and lies underneath the hard palate when the tongue is at rest The remainder of the body of the tongue may be divided into the center, which is partly beneath the hard palate and partly beneath the soft palate, the back, which is beneath the soft palate, and the root, which is opposite the back wall of the pharynx.
Bearing all these terms in mind, say the word “peculiar” and try to give a rough description of the actions of the vocal organs during the consonant sounds. You should find that the lips come together for the first sound. Then the back and center of the tongue are raised. But is the contact on the hard palate or on the velum? (For most people it is centered between the two.) Then note the position in the formation of the l. Most people make this sound with the tip of the tongue on the alveolar ridge.
Now compare the words "true" and "tea." In which word is the tongue contact further forward in the mouth? Most people make contact with the tip or blade of the tongue on the alveolar ridge when saying "tea," but slightly farther back in "true." Try to distinguish the differences in other consonant sounds such as those in "sigh" and "shy" and those in "fee" and "the."

Articulatory Phonetics: