While you are working with these two sounds /ǝ/ and /ɜː/ there are some other useful insights to be gained. Although these two central vowels have different symbols, they are for our practical classroom purposes formed with the tongue, lips and jaw in the same position, that is with the tongue, lips and jaw relaxed and as far as possible without muscle tone (and if this is not clear then revisit Episode 18 before you continue).
However there is a difference which is crucial for spoken English: while the vowel quality is practically the same, /ǝ/ is always unstressed, short, minimal, while /ɜː/ is stressed, long and clear.
So this brings us to an interesting and illuminating question: If the two sounds have (almost) identical vowel qualities, what else is it that we are hearing when we hear the difference?
Lung or pulmonic pressure, the basis of stress
A large part of the answer is that in /ɜː/ we are hearing (aside from its length) the extra volume and power of the sound, caused by extra lung pressure brought to bear on the exhalation that is producing the sound. To put it differently the stream of air forced out of the lungs and through the vocal cords is under greater pressure for /ɜː/ than for /ǝ/. This pressure is produced by the muscles. Technically this is referred to as pulmonic pressure, which just means that lungs provide the pressure. And this is precisely the pressure that is used to stress an English syllable, so it is worth getting to feel this muscular pressure in the body, to develop the awareness or proprioception of this lung pressure, in order to be able to help our learners to operate the stress system. And we could call this pulmonic pressure the fifth muscle button (see my May 2012 post Making pronunciation physical: Finding the ‘muscle buttons’.
So far this is just words, so here are three simple exercises for you and your students to get to the heart of what makes a syllable stressed. First making use of the /ǝ/ and /ɜː/ distinction.
Pulmonic pressure Ex 1
Say /ǝ/ and /ɜː/ alternately, and notice:
1) the greater volume of /ɜː/
2) the greater muscular effort of your lungs when producing /ɜː/. You can notice this by putting you hands on your chest, and on your abdomen, and on your sides. You may also be able to notice stronger air flow out of the mouth. What you are noticing here is pulmonic pressure.
Pulmonic pressure Ex 2
Now try this with a fricative consonant, and if we take a voiceless one you may find this easier to observe.
Say /f/ and make it last a couple of seconds. Now say it more strongly as if it is stressed like this /’ff/. You will immediately be able to hear the higher air pressure producing a stronger version of /f/
But now alternate greater and lesser lung pressure so that you can really get the feeling in your body of what your lungs have to do to stress a syllable
Like this /ff…’ff…ff…’ff…ff…’ff…/
You should have the sensation of alternating strong lung pressure with weak lung pressure.
Pulmonic pressure Ex 3
Do the same thing with another unvoiced fricative consonant /s/.
Say /s/ and make it last a couple of seconds. Now say it more strongly as if it is stressed like this /’ss/. Again you will be able to hear the higher air pressure producing a stronger version of /s/
Now alternate the two so that you can really get the feeling in your body of what your lungs have to do to stress a syllable
Like this /ss…’ss…ss…’ss…/
And once again you should have the sensation of alternating strong lung pressure with weak lung pressure.
This may not seem much, but one day you may suddenly realise what a breakthrough this is! This pulmonic lung pressure is the basis of stress, and its absence is the basis of unstress…
And as I said we might call this the fifth muscle button…