Speech as a Remarkable Motor Skill

lmjohns325 June 2015

In April I got to attend the annual meeting of the Society for the Neural Control of Movement, a small but interesting conference that brings together researchers in neuroscience, physiology, biomechanics, robotics, and computational modeling to discuss recent progress in motor control.

The conference has a single track as well as a poster session. What this means is that everyone at the conference piles into a large room in the morning and sits there listening to presentations, one after the other, for a few hours. At lunch everyone leaves the room and goes upstairs to eat and stand around in another large room discussing the posters that are up that day. Then in the afternoon everyone goes back downstairs and sits in the first large room again, listening to more talks.

After each of the talks in the morning and the afternoon, there is usually a short time for “questions” from the audience. During this time, a few people in the audience get up from their seats and approach a microphone to ask the speaker a “question.” (Sometimes this “question” is actually a monologue about that person’s own research work, but at this year’s conference I was impressed by how little this happened.)

This year, I had an interesting and amusing vision during one of these question periods. I happened to be sitting next to the microphone, and so I watched—in profile and from slightly below—as a person stood up and spoke into the microphone to ask their question. From this perspective, as the person talks, one can see clearly the vibrations produced by the vocal cords on the surrounding tissue, as well as the rapid and coordinated movements of many of the muscles in the throat, face, and lips.

One of the difficult things in thinking about speech is how effortless speech is. When we talk with another person, the sounds that we produce somehow seem mostly automatic. Likewise, the sounds that they produce form, with little to no conscious effort on our part, a coherent percept of a spoken word, not a bunch of colliding frequencies with different power levels. Much like looking out a window and seeing not photons but an entire scene, a configuration of the world, listening to speech sounds (particularly during an interpersonal interaction) leads almost automatically to understanding of not just the speech, but even the meaning of the speech. In both cases it takes conscious effort to perceive the underlying substrate that carries this information into our brains: for an image, it is quite difficult to become aware of the light that forms the image in your eye; for speech, it is quite difficult to become aware of the sounds or the movements that generate the speech.

So I was sitting there watching this person ask a question at the microphone, but suddenly instead of automatically hearing the question being asked, I perceived the state of the person doing the asking. Here before me stood a large mammal, craning its neck forward towards a microphone, making incredibly intricate, coordinated muscle movements that generated an equally intricate, coordinated pattern of sounds into the microphone!

Producing a speech signal using muscles is a pretty amazing feat in its own right, but my imagination in that moment went even further. The animal I was watching was a human, but what, I thought, if this animal had been some other species? A dog, a bird, a lizard, or a dolphin? Suppose for a moment that a dog had been standing there at the microphone, moving its snout in this intricate, coordinated way to produce some sort of sound that we could interpret as speech. People would come from miles around to see this feat of nature! This dog would be famous! (In fact, there are a number of relatively famous online videos showing dogs making “speech-like” sounds.)

Now, I know that dogs can’t produce speech sounds (in general). But thinking about speech as a pattern of muscle movements, I think, helps highlight how unusual our speaking abilities are, and how remarkable speech is. And speaking is only one example: humans have remarkable motor abilities in many different domains! We can, for example, with some practice, swing a golf club through the air, make contact with a small golf ball a couple meters from our eyes, and send that ball hundreds of meters away—there are even people who can do this so that the golf ball lands within a few meters of a desired target, on nearly every single trial!

I love watching the beginning of Daniel Wolpert’s TED talk about movements, because I, too, am a movement chauvinist. While I think the modern human brain is a bit more interesting than just being devoted to movements, I agree that movements are a crucial—perhaps the crucial—feature of our existence. So let’s all think a bit more about movement and its implications for speech! I’m convinced that this path leads somewhere interesting.