DAF: Delayed Auditory Feedback

Some of you may have heard about a ‘miracle cure’ that came out a few years ago for stuttering. One of the brand names is Speech Easy. Here is a heartwarming video demonstrating just how amazing the device is: a person can go from a severe stutter to fluent speech by simply inserting what looks like a hearing aid into the ear and turning it on. Immediate effects. (skip to about 5min in to see the actual heart-wrenching).

The principle behind the device is Delayed Auditory Feedback. The speaker’s voice is echoed back in their ear with a delay of about 50ms (give or take). The hypothesis of why it works is that it creates a situation like choral speech that typically increases fluency (ie. it is like someone is speaking with you). Being an SLP student I get to learn about these amazing things, in fact, I take a whole class (6 hours a week!) in just stuttering. There is, of course, a catch because there always is. The effects of the device tend to wear off after some time as the brain gets used to the echo. It isn’t a replacement for treatment and actual control of stuttering but may be a wonderful option for someone who is desperate, who stutters severely and who has tried everything.

The science behind it is interesting. Technology that causes stutterers to become more fluent can cause disfluent speech in nonstutterers. In class I volunteered to read a passage aloud while wearing headphones and the professor would switch on DAF at random intervals. My speech became slow, disfluent, repeating syllables, prolonging sounds. I didn’t stutter exactly but I stumbled over my words much more than I normally would. Someone tried it before I did and, not wanting to be shown up, I tried to read even faster. Impossible! Every time I would try to speed up I would just start stringing together almost unintelligible syllables.

You can try it yourself. Do it with a friend because you may not realize just how different you sound. Download this software (it is free as a trial). Crank up the delay to approx 150-200ms (although try a range to see what causes the biggest effect). Wear some headphones and turn up the volume. Now read a passage. Try speeding up. Slow down. What happens?

Science rules. Ps. You’ll need to have a microphone /built-in mic in order to do this activity.

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