Breathing for Speech

Neuroscientist Sophie Scott will be speaking at The Voice, an evening event on Friday 1 March at Wellcome Collection that explores the unexpected qualities of voices in all their forms. Here, she explains the importance of breathing for our ability to talk.

For animals with lungs, breathing is obviously central to life, making metabolism possible. What can be somewhat less obvious is that for humans, breathing is also central to speech, and the way that we breathe when we speak is very different to the way that we breathe to stay alive (called metabolic breathing). If you use a breath belt to look at the movements of the rib cage during metabolic breathing, you see a very regular, almost sinusoidal profile of expansion as air is drawn in, followed by an elastic contraction that forces air out:

Slide1

When we breathe to speak, we breathe very differently, taking in a breath and then using our intercostal muscles and diaphragm to control a fine flow of air through our larynx. This enables us to produce a (relatively) lengthy utterance and to control aspects of the loudness and pitch of our voice. Although we think of speech as being to do with our larynx and our articulators, our voices are only really possible at all because of how we breathe.

We start to breathe for speech by using our intercostal muscles initially to prevent air from flooding out through the larynx, and to keep a constant pressure of air at the larynx (called subglottal pressure). Towards the end of a breath, we need to use our intercostal muscles to squeeze air out, and if you keep speaking long after you want to take another breath, your voice starts to fall apart, as this soundclip demonstrates:

The next image shows what happens to the movements of my chest wall (reflecting the actions of the intercostal muscles) when I speak this way. You can see that, unlike metabolic breathing, the movements of the intercostal muscles are much more constant, and that as I keep speaking without taking another breath, the intercostal muscles are starting to squeeze the air out – followed by a big inspiration as I take another breath – then some rapid spasms of the intercostal muscles, which is due to me laughing!

Slide2

Strikingly, we can only breathe this way because we walk upright, which means that we don’t need to use our ribcages to support our weight. If you try and speak while using your ribcage to support your weight – for example, while doing press-ups – you get a sense of how hard this would be. The development of this fine control of our intercostal muscles was central to the evolution of human speech, and although we don’t typically think much about how we breathe to speak, we in fact have as much fine control of our intercostal muscles as we have of our fingers.

The fine flow of air from our lungs is just the start of the story of speech, but it’s an essential and often overlooked aspect. Of course, breath control is central to other ways that we use our voices – to sing, beat box or rap – and I’ll be discussing breathing and the human voice in greater detail in my talk.

The Voice takes place at Wellcome Collection on Friday 1 March.

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