Speech-Language Pathology/Stuttering/How Anti-Stuttering Devices Work

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Changing how stutterers hear their voices improves fluency. This can be done in many ways:

  • Speaking in chorus with another person.
  • Hearing your voice distorted.
  • Hearing your vocal fold vibration (phonation) without hearing the articulation of your lips, jaw, and tongue.
  • Hearing a synthesized sound mimicking your phonation (masking auditory feedback, or MAF).
  • Hearing your voice delayed a fraction of a second (delayed auditory feedback, or DAF).
  • Hearing your voice shifted higher or lower in pitch (frequency-shifted auditory feedback, or FAF).

Together these phenomena are called altered auditory feedback.

No brain scans have looked at stutterers' auditory processing while speaking with altered auditory feedback.[1] However, one hypothesis is that introducing errors targeted at the area that integrates auditory and somatic processing increases blood flow to that area. In other words, hearing what you're saying out of sync with what you feel your muscles doing raises a red flag. The red flag is raised in the area that's abnormally underactive in stutterers. Increased blood flows to this area. The activity level increases to normal, and stuttering diminishes.

The errors must not raise red flags in other brain areas, such as language processing. E.g., when you walk up to Fred and say, "Hi, Fred," a device that whispered in your ear, "Hi, Steve" likely wouldn't improve fluency.

Non-stutterers have difficulty speaking with altered auditory feedback. Most can't count to ten. They repeat or skip numbers, or giggle uncontrollably, then rip the headphones off. If altered auditory feedback increases blood flow to the auditory/somatic integration area, then in non-stutterers the devices raise activity to an abnormally high level. Too much activity is as bad as not enough activity. Interestingly, the effects of too much activity in this area are somewhat like stuttering&#151;repeating words, or not being able to get words out.

Planum Temporale Abnormality and DAF[edit | edit source]

DAF effectiveness is has been associated with planum temporale (PT) abnormality.[2] [3]

DMAF device uses vocal tone to improve fuency. The device is called StutterFree™ This effect is unlike DAF as it is not a temperary effect device but has proven perminate in some cases. Mostly works for children.

Immediate Effects of Anti-Stuttering Devices[edit | edit source]

The most effective types of altered auditory feedback are delayed auditory feedback (DAF) and frequency-shifted auditory feedback (FAF). Each reduce stuttering about 70%, immediately, without training, speech therapy, mental effort, or abnormal-sounding speech. Combined DAF/FAF reduces stuttering about 80%.

70-80% is the average improvement found in dozens of studies, with hundreds of stutterers.[4] Rarely does DAF and/or FAF improve anyone's speech more than 90%, or less than 50%. If auditory processing underactivity were the only cause of stuttering, then DAF/FAF devices would make all stutterers 100% fluent. The 70-80% effectiveness shows that auditory processing underactivity is a factor in stuttering, but not the only factor. To get closer to 100% fluency an anti-stuttering device has to be combined with speech therapy.

Should Adults Use Anti-Stuttering Devices?[edit | edit source]

Hypothetically, the only treatment for stutterers' auditory processing abnormality is an altered auditory feedback device. No speech therapy is known to correct this abnormality.

Many people overcome stuttering by treating the other factors. But using an anti-stuttering device in conjunction with other therapies may make the other therapies easier, faster, and more effective. If so, you'll then need your anti-stuttering device less and less.

Even if you have success with speech therapy and can talk fluently in most situations, there will be a few situations in which you stutter. E.g., you may want an anti-stuttering device for public speaking.

Keep an anti-stuttering device plugged into your telephone can be an easy way to do speech therapy. If the device produces carryover fluency, after a few calls your speech may be improved for the rest of the day. Many states provide telephone-compatible anti-stuttering devices free.

Should Children Use Anti-Stuttering Devices?[edit | edit source]

For children under six, stuttering therapy is usually 100% effective, so anti-stuttering devices are unnecessary.

With seven- to thirteen-year-olds, DAF devices are usually used in school with a speech-language pathologist. Because such therapy is usually effective[5] [6] there's no need for a child to use an anti-stuttering device outside of therapy. However, if a child sees his speech-language pathologist for only ten or twenty minutes once or twice a week, the speech-language pathologist could train the parents to supervise their child practicing with a DAF device at home every day, to increase therapy time. A typical protocol for home therapy is ten minutes reading aloud, a ten-minute conversation with a family member, and a ten-minute telephone call (perhaps to a grandparent). Or the parent and child could play Say the Magic Word while driving to school.

We don't know whether children who stutter have the same neurological abnormalities as adult stutterers. Altering a child's brain activity might cause his brain to develop in a different way. Extensive use of an anti-stuttering device might cause the child's brain to develop normal auditory processing and the child would outgrow stuttering. But maybe extensive use of an anti-stuttering device would cause the child's brain to develop in another, unknown abnormal way.

Some anti-stuttering devices impair the user's hearing by occluding (blocking) the ear that the device is in. And some devices pick up, distort, and amplify background noise. If a child can't hear his teacher, he'll fall behind in school. He might get hit by a bus that he didn't hear coming. Users of some anti-stuttering devices have reported symptoms of permanent hearing damage, such as ringing in the ears or pain from loud noises.


  1. ^ Watkins, K., S. Davis, P. Howell. Brain activity during altered auditory feedback: an fMRI study in persistent and recovered developmental stuttering, Oxford Dysfluency Conference (2005), found that for stutterers and non-stutterers DAF increased activity in the supplementary motor area, and DAF and FAF increased activity in the superior tem-poral cortex. The stutterers showed underactivity in the speech motor control area (opposite to what other studies found) and overactivity of the cerebellum.
  2. ^ Foundas, A.L., Bollich, A.B., Corey, D.M., Hurley, M., Heilman, K.M. "Anomalous Anatomy in Adults with Persistant Developmental Stuttering: A Volumetric MRI Study of Cortical Speech-Language Areas," Neurology, 2001 57:207-215.
  3. ^ A. L. Foundas, MD, A. M. Bollich, PhD, J. Feldman, MD, D. M. Corey, PhD, M. Hurley, PhD, L. C. Lemen, PhD and K. M. Heilman, MD. "Aberrant auditory processing and atypical planum temporale in developmental stuttering," Neurology, 2004;63:1640-1646.
  4. ^ Kalinowski, J., Armson, J., Stuart, A., Graco, V., and Roland-Mieskowski, M. "Effects of alterations in auditory feedback and speech rate on stuttering frequency," Language and Speech, 1993, 36, 1-16; 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; Brenaut, L., Morrison, S., Kainowski, J., Armson, J., Stuart, A. "Effect of Altered Auditory Feedback on Stuttering During Telephone Use," Dalhousie University, Halifax, Nova Scotia, Canada, 1995; Stager, S., Denman, D., Ludlow, C. "Modifications in Aerodynamic Variables by Persons Who Stutter Under Fluency-Evoking Conditions." Journal of Speech, Language, and Hearing Research, 40, 832-847, August 1997. Zimmerman, S., Kalinowski, J., Stuart, A., Rastatter, M. "Effect of Altered Auditory Feedback on People Who Stutter During Scripted Telephone Conversations." Journal of Speech, Language, and Hearing Research, 40, 1130-1134, October 1997.
  5. ^ 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.
  6. ^ 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.