If stuttering is learned, why is it so difficult to treat? To answer that question, Kehoe turns to the discipline of motor learning theory, which proposes two different ways people control their actions: closed-loop and open-loop. In closed-loop control, you continually adjust your actions based on sensory data received from your sense organs-threading a needle, for example. The process is relatively slow (mean elapsed time between sensation and response is about 200 milliseconds) but is also accurate and flexible, and it requires no practice.

But many activities-gymnastics, playing the piano, and speech, to name a few-require much faster response than 200 milliseconds. Talking at normal pace (producing 1,200 phonemes, or distinctive individual sounds, per minute) requires a response rate of 50 milliseconds per phoneme. These speeds require open-loop control, in which information processing is done before the movement begins. The movements are learned beforehand as a result of practice and require no conscious thought. They are also inflexible-and prone to error.

Unlearning such behaviors is about as easy as an English-speaking adult becoming fluent in Chinese, but in fact all stutterers are capable of fluent speech under the right conditions. The goal of speech therapy is for stutterers to learn new patterns of speech, retraining the way they form syllables. At first, new patterns require a conscious effort, but repetition will eventually make them automatic-in theory, at least. In practice, unfortunately, the old patterns tend to reassert themselves once stutterers leave the speech clinic.

Kehoe's innovation was to build electronic devices that improve stutterers' fluency. One of his patents is on a bio-feedback system that listens to the user's speech and trains the user to speak without stuttering, eventually without the device.

There's no question that Kehoe's inventions work. A study published in the October 1997 Journal of Speech, Language, and Hearing Research reported that the devices reduced stuttering on average 73 percent, without training or speech therapy.

Why does hearing an echo of your own voice reduce stuttering? Kehoe's theory is that delayed feedback sets off alarm bells in the rear-brain sensory areas, shunting extra blood to the back of the brain, which improves auditory processing and inte-gration. The back of the brain forwards the extra sensory input to the front of the brain, but the delay is too short for the front to detect, so speech is not disrupted. "The result is extra information for improved motor control and fluent speech," says Kehoe.

Kehoe's emphasis on motor learning theory certainly bucks the current wisdom among academic speech researchers. In those circles, he concedes, "this is not a popular idea." But response from speech pathologists who actually treat stutterers has been overwhelmingly positive. "They love me," he says. "I make their jobs easier."

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