Speech-Language Pathology/Stuttering/Delayed Auditory Feedback
Delayed auditory feedback (DAF) can be used two, very different ways. The delay can be set between 50 and 70 milliseconds to reduce stuttering about 70% at a normal speaking rate, without training, mental effort, or abnormal-sounding speech.
DAF can also be used to support the fluency shaping target of slow speech with stretched vowels. For this purpose the delay is usually set at 200 milliseconds and then reduced to shorter delays (as short as 75 milliseconds) over the course of the therapy program.
For this latter purpose, a speech-language pathologist must train the stutterer. When the stutterer can complete a simple speaking task, such as counting to ten, using the slow speech target correctly, then he can use a DAF device. DAF therapy then has two goals:
- To increase the length and complexity of the utterance, and increase the stress of the speaking situation, while using the DAF device to support on-target fluent speech.
- To reduce the need for the DAF device, until the stutterer no longer needs the device.
For the first goal, after the stutterer can count to ten using the slow-speech target correctly (e.g., all syllables stretched equally, all syllables stretched to one or two seconds, no pauses between words, and no dysfluencies) without the DAF device, then use the device to have a conversation at the same slow speaking rate. When the stutterer can achieve the slow speech target with 100% fluency using the DAF device for utterances with the length and complexity of normal conversations, then the stutterer should take the device out of the speech clinic and use it in increasingly stressful conversations. The first goal is speech that is 100% fluent and on-target (i.e., slow) in any conversation. For a severe stutterer, this may mean using one- or two-seconds per syllables speech with the device set at 200 milliseconds.
When the stutterer achieves the first goal, then he gradually reduces his dependence on the device. He decreases the delay and increases his speaking rate. But if he has any dysfluencies he should go back to the longer delay and slower speaking rate. He can also decrease the volume, and use the device in one ear instead of both ears. He can use the device at the beginning of conversations, and then turn it off when he feels capable of speaking on target with the support of the device. He can discontinue using the device in low-stress conversations. Then he can discontinue using the device in medium-stress conversations, reserving the device only for stressful conversations such as public speaking. Eventually he should need the device only occasionally.
Mistakes in DAF Use 
The common mistake with DAF is using a normal speaking rate with a long (slow) delay. If you want to talk at a normal speaking rate, set the DAF delay between 50 and 75 milliseconds. Don't use a delay longer than 75 milliseconds unless you're using closed-loop slow speech.
The typical mistake is for a stutterer to experience a 50% fluency improvement at 50 milliseconds and then a 75% improvement at 75 milliseconds. He sees that the dial goes up to 200 milliseconds. He thinks, "I'll crank up this baby! I'll redline it! I'll turn it up all the way to 200 milliseconds and I'll be 200% ﬂuent!"
DAF doesn't work like that. 200 milliseconds is for speech ﬁve to ten times slower than normal. Non-stutterers can't talk normally with a 200-millisecond delay (with rare exceptions due to a linguistic abnormality) but most stutterers are capable of forcing themselves to "tune out" the delay. This appears to be due to stutterers' auditory processing underactivity. In other words, if you use DAF incorrectly you may be able to make your auditory processing underactivity worse. This may explain why some stutterers have reported that a DAF device lost effectiveness or "wore off" over time.
Another mistake is to use a DAF device in low-stress situations (such as reading aloud) and expect carryover to high-stress situations. Carryover works the other way. For example, a child could use a DAF device only when called on to speak in class. Or an adult could a DAF device when speaking on the radio at work, but not for conversations with his wife at home. As a rule, use an anti-stuttering device in situations in which you stutter, and don't use it in situations where you speak fluently.
Long-Term Effects of DAF 
Nine adult stutterers used DAF devices thirty minutes per day, for three months. The thirty minutes consisted of ten minutes reading aloud, a ten-minute conversation with a family member, and a ten-minute telephone call. The subjects received no speech therapy.
The devices were used with binaural (two ears) headsets. The subjects were allowed to set the delay where they wanted. Most selected delays around 100 milliseconds.
Long-Term Effects of DAF
Before three months of DAF use, the subjects stuttered on 37% of words, on average. When they put on the DAF device their stuttering dropped to 10%. I.e., the device improved their speech about 70%.
Three months later the subjects stuttered on 17% of words, when not using the DAF device. When wearing the DAF device they stuttered on 13% of words.
This shows that, when not wearing the devices, the subjects' stuttering diminished from 37% of words to 17% of words, or a 55% improvement. This is "carryover fluency." Put another way, the devices trained the users to need the devices less.
The increase (from 10% to 13%) in stuttering when wearing the devices wasn't statistically significant. Examining this more closely, stuttering when wearing the device increased only for "automatic speech," such as reciting days of the week, and for repeating words and sentences after the examiner. No change in effectiveness was found in conversations or in a "picture description" task. This suggests that any "wearing off" effects occurred in less-important speaking situations.
The "carryover fluency" effect was the same across all speaking tasks.
In another study, an eleven-year-old boy received fourteen hours of structured therapy with mediated learning and a School DAF. His stuttering diminished from 9% dysfluencies to 4.8% dysfluencies (when speaking without the device, a 47% improvement). One year later he still had 4.8% dysfluencies. Another fourteen hours of treatment reduced his stuttering to 4.1% dysfluencies.
Two other studies combined speech therapy with a DAF device. One study was of adults, the other of children. Both studies found that combining DAF and stuttering therapy trained the subjects to speak fluently (less than 2% stuttering) and no longer need the devices.
- ^ Sark, S., Kalinowski, J., Stuart, A., Armson, J. "Stuttering amelioration at various auditory feedback delays and speech rates," European Journal of Disorders of Communication, 31, 259-269, 1996.
- ^ Van Borsel, J., Reunes, G., Van den Bergh, N. "Delayed auditory feedback in the treatment of stuttering: clients as consumers," International Journal of Language and Communication Disorders, 2003, 38:2, 119-129.
- ^ Radford, N., Tanguma, J., Gonzalez, M., Nericcio, M.A., Newman, D. "A Case Study of Mediated Learning, Delayed Auditory Feedback, and Motor Repatterning to Reduce Stuttering," Perceptual and Motor Skills, 2005, 101, 63-71.
- ^ Ryan, B.P., Van Kirk, B. "The Establishment, Transfer and Maintenance of Fluent Speech in 50 Stutterers Using Delayed Auditory Feedback and Operant Procedures." Journal of Speech and Hearing Disorders, 39:1, February, 1974.
- ^ Ryan, Bruce and Barbara Van Kirk Ryan. "Programmed Stuttering Treatment for Children: Comparison of Two Establishment Programs Through Transfer, Maintenance, and Follow-Up," Journal of Speech and Hearing Research, 38:1, February 1995.