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 | Subject: The physics and physiology of speech  Fri Aug 20, 2010 4:44 am | |
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The physics and physiology of speech
Man is distinguished from the other primates by having the apparatus to make the sounds of speech. Of course most of us learn to speak without ever knowing much about these organs, save in a vague and general sense - so that we know how a cold or sore throat alters our own performance. Language scientists have a very detailed understanding of how the human body produces the sounds of speech. Leaving to one side the vast subject of how we choose particular utterances and identify the sounds we need, we can think rather simply of how we use our lungs to breathe out air, produce vibrations in the larynx and then use our tongue, teeth and lips to modify the sounds. The diagram below shows some of the more important speech organs.
This kind of diagram helps us to understand what we observe in others but is less useful in understanding our own speech. Scientists can now place small cameras into the mouths of experimental subjects, and observe some of the physical movements that accompany speech. But most of us move our vocal organs by reflexes or a sense of the sound we want to produce, and are not likely to benefit from watching movement in the vocal fold.
The diagram is a simplified cross-section through the human head - which we could not see in reality in a living speaker, though a simulation might be instructive. But we do observe some external signs of speech sounds apart from what we hear.
A few people have the ability to interpret most of a speaker's utterances from lip-reading. But many more have a sense of when the lip-movement does or does not correspond to what we hear - we notice this when we watch a feature film with dubbed dialogue, or a TV broadcast where the sound is not synchronized with what we see.
The diagram can also prove useful in conjunction with descriptions of sounds - for example indicating where the airflow is constricted to produce fricatives, whether on the palate, the alveolar ridge, the teeth or the teeth and lips together.
Speech therapists have a very detailed working knowledge of the physiology of human speech, and of exercises and remedies to overcome difficulties some of us encounter in speaking, where these have physical causes. An understanding of the anatomy is also useful to various kinds of expert who train people to use their voices in special or unusual ways. These would include singing teachers and voice coaches for actors, as well as the even more specialized coaches who train actors to produce the speech sounds of hitherto unfamiliar varieties of English or other languages. At a more basic level, my French teacher at school insisted that we (his pupils) could produce certain vowel sounds only with our mouths more open than we would ever need to do while speaking English. And a literally stiff upper lip is a great help if one wishes to mimic the speech sounds of Queen Elizabeth II.
So what happens? Mostly we use air that is moving out of our lungs (pulmonic egressive air) to speak. We may pause while breathing in, or try to use the ingressive air - but this is likely to produce quiet speech, which is unclear to our listeners. (David Crystal notes how the normally balanced respiratory cycle is altered by speech, so that we breathe out slowly, using the air for speech, and breathe in swiftly, in order to keep talking). In languages other than English, speakers may also use non-pulmonic sound, such as clicks (found in southern Africa) or glottalic sounds (found worldwide). In the larynx, the vocal folds set up vibrations in the egressive air. The vibrating air passes through further cavities which can modify the sound and finally are articulated by the passive (immobile) articulators - the hard palate, the alveolar ridge and the upper teeth - and the active (mobile) articulators. These are the pharynx, the velum (or soft palate), the jaw and lower teeth, the lips and, above all, the tongue. This is so important and so flexible an organ, that language scientists identify different regions of the tongue by name, as these are associated with particular sounds. Working outwards these are:
* the back - opposite the soft palate
* the centre - opposite the meeting point of hard and soft palate
* the front - opposite the hard palate
* the blade - the tapering area facing the ridge of teeth
* the tip - the extreme end of the tongue
The first three of these (back, centre and front) are known together as the dorsum (which is Latin for “backbone” or “spine”)
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