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Anti-stuttering devices are a variety of electronic devices to help improve the fluency of persons who stutter.
This article uses the following terms:
- Immediate fluency is the reduction in stuttering (if any) while the stutterer is using the anti-stuttering device.
- Carryover fluency is the reduction in stuttering (if any) after the stutterer removes the device.
- Wearing off of effectiveness or adaptation effect occurs when a stuttering treatment is effective when first used, but the effectiveness diminishes over time (days, weeks, or months).
- Transfer refers to learning to speak fluently in a speech clinic, and then transferring this fluent speech to higher stress conversations outside the speech clinic.
History of Anti-stuttering Devices
It has long been known that when a stutterer speaks in chorus with another person, the stutterer usually speaks more fluently. An example of this is reciting the Pledge of Allegiance as part of a group.
Metronomes were the first anti-stuttering device, used mostly between about 1925 and about 1975. Speech-language pathologists trained stutterers to slow down their speech and speak one syllable for each beat of the metronome. One study 100% eliminated stuttering using a metronome to speak at 92 syllables per minute.1 This is about three times slower than normal speech.
The Edinburgh Masker anti-stuttering device was popular in the early 1980s. The device measured the fundamental frequency of the user's voice (the frequency at which his or her vocal folds vibrate) and synthesized a sine wave at this frequency. (Vocal fold vibration is a sine wave.) A long-term non-clinical study of 67 stutterers who used the Edinburgh Masker users for six months found that 82% said the device continued to be highly effective. 67% said that, "as the result of using the device, their unaided speech ﬂuency had improved" (carryover fluency) The average volume was 78 dB.3
Delayed auditory feedback (DAF) was first used to reduce stuttering in 1964. A DAF user hears his or her voice in headphones, delayed a fraction of a second. Typical delays are in the 50 millisecond to 200 millisecond range (one-twentieth to one-fifth of a second). DAF was believed to reduce stuttering by slowing the speaking rate of users. For example, a 195 millisecond delay reduced stuttering 85% while also slowing speaking rate 60%.1 DAF was used in fluency shaping stuttering treatment programs to induce a slow speech rate. Speech-language pathologists then trained stutterers to use fluent speech motor skills such as relaxing their breathing, vocal folds, and lips, jaw, and tongue during speech. After stutterers mastered these fluent speech motor skills at slow speaking rates, speech-language pathologiusts trained stutterers to increase their speaking rate while maintaining these fluent speech motor skills. Eventually the stutterers were trained to speak fluently at normal speaking rates. Such stuttering treatment programs did not encourage stutterers to use DAF devices outside of the speech clinics. The result, unfortuneatly, was that some stutterers learned to speak fluently in low-stress conversations in a speech clinic but were unable to transfer their fluent speech motor skills to normal stress conversations outside of the speech clinic.
In 1993, a study found that DAF reduced stuttering at both normal speaking rates and fast speaking rates.2 This study also found that a new type of altered auditory feedback called frequency-altered auditory feedback (FAF) also reduced stuttering at normal speaking rates, as well as at fast speaking rates. A user of FAF hears his or her voice in headphones shifted higher or lower in pitch, typically one-half octave. Many studies found that DAF and FAF reduce stuttering in the 60-80% range, at normal speaking rates, without the users' speech sounding abnormal, without training or speech therapy, typically while reading aloud in a speech clinic. Combining DAF and FAF is generally more effective than DAF or FAF alone. 2 4 5 6 7 8 9 10 These studies led to the current trend of using anti-stuttering devices prosthetically, that is, without speech therapy.
Also in the 1990s, neuroscientists began conducting brain scan studies of stutterers. These studies found, in general, two abnormalities during stuttering:11
- Stutterers appear to have underactivity in the central auditory processing area, suggesting that one component of stuttering is an auditory processing disorder.
- Stutterers appear to have overactivity in the speech motor control area. This may explain why stuttering is characterized by overtense speech production muscles, and stuttering therapy programs often train stutterers to speak with relaxed speech-production muscles.
No brain scan studies have examined stutterers using anti-stuttering devices. Hypothetically, anti-stuttering devices affect the brains of stutterers in one or both of two ways: increasing activity in the auditory processing area, and/or reducing speech motor activity. Such a dual model hypothesis may explain why there seems to be a wide range of effects from anti-stuttering devices: some devices may affect the auditory processing area but not the speech motor area, or vice versa, or both, etc.
The FDA Modernization Act of 1997 deregulated anti-stuttering devices. Manufacturers are no longer required to prove that their anti-stuttering devices are safe or effective before selling such devices in the United States.
Childhood Safety Issues
A stuttering treatment that alters how a child's brain functions, including anti-stuttering devices and anti-stuttering medications, risks causing the child's brain to develop on yet another, unknown developmental track. Parents who are concerned about this issue may want to seek a non-device, non-medication stuttering treatment for their young child, or
- Have the child use an anti-stuttering device only for limited periods, such as less than thirty minutes per day
- Have a speech-language pathologist monitor the child's speech.
Hearing Safety Issues
Adults and children should consider the importance of hearing since some anti-stuttering devices impact a user's hearing when wearing the device. It is also possible that some anti-stuttering devices might cause permanent hearing damage. Consumers should:
- Keep the volume down to a comfortable listening level.
- Discontinue using an anti-stuttering device if you experience ringing in your ears or pain in your ears, especially after loud noises around you.
- Discontinue using an anti-stuttering device that picks up sounds other than your speech.
- Discontinue using an anti-stuttering device that has feedback (screeching) after loud noises.
- Get your hearing tested before using an anti-stuttering device, thirty days later, and then annually.
Difference between Anti-stuttering Devices
Some anti-stuttering devices are intended to be used in a speech clinic, as part of a stuttering treatment program. Other anti-stuttering devices are intended to transfer speech therapy skills to normal-stress conversations outside of a speech clinic. Still other anti-stuttering devices are intended to be used without speech therapy.
Types of Altered Auditory Feedback
Most anti-stuttering devices provide DAF, and most research has been done using DAF. A few provide other types of altered auditory feedback.
- FAF changes the pitch or frequency at which the user hears his or her voice. Many studies have found FAF to be effective,2 4 5 6 7 8 9 10 yet many questions remain. For immediate fluency, upshifts and downshifts are equally effective for reducing stuttering, but studies with non-stutterers found that FAF induces changes in vocal fold tension.12 Hypothetically, FAF upshift devices might improve stutterers' auditory processing and result in immediate fluency, but train stutterers to speak with increased vocal fold tension and result in "wearing off" of effectiveness or even make speech worse over time. FAF downshift devices might train stutterers to speak with relaxed vocal folds and improve carryover fluency. More research is needed in this area.
- All FAF research has used octave-scale pitch-shifting. Such devices can shift a user's voice higher or lower in pitch, typically one-half or one octave. Other anti-stuttering devices use frequency-shifting instead of pitch-shifting. Such devices typically add or subtract 500 Hz, 1000 Hz, or 2000 Hz to the user's voice. No studies have investigated whether frequency-shifting FAF has an effect on stuttering. Frequency shifting can also only result in the user hearing his or her voice higher; it's incapable of producing a lower-sounding voice.
- MAF is the only type of altered auditory feedback that pulls stutterers out of silent blocks. Few stutterers have such blocks when using DAF and/or FAF, but a few need MAF.
- Some anti-stuttering devices use a special microphone to pick up the user's vocal fold vibrations (phonation). Little research has been done investigating the effectiveness of this type of altered auditory feedback.
- Size. Anti-stuttering devices range from computer-based, typically used with a full-size headset; to the size of an iPod, typically used with miniature earsets made for cellphones; to the size of a hearing aid.
- Background noise rejection. Some anti-stuttering devices, such as those designed to be used in quiet speech clinics, have no anti-background noise features. Other anti-stuttering devices have features to reject background noise. The latter is important if the anti-stuttering device will be used in a noisy classroom or restaurants.
- Monaural or binaural. Binaural (two ears) anti-stuttering devices are about 25% more effective than monaural (one ear) anti-stuttering devices.13
- Frequency range. Many stuttering therapy programs focus on improving vocal fold awareness and control ("gentle onsets," "easy onsets," etc.). Adult male vocal folds vibrate around 125 Hz; women's and children's vocal folds vibrate around 200 to 250 Hz. Some anti-stuttering devices can reproduce such frequencies, but other anti-stuttering devices can only reproduce higher frequencies. No research has investigated whether limiting frequency range reduces the effectiveness of an anti-stuttering device.
List of Anti-stuttering Devices
- DAF/FAF Assistant
DAF/FAF Assistant is software that runs on Windows computers and personal digital assistants.
The Defstut is an iPod-size anti-stuttering device providing DAF.
- Desktop FluencyCoach
Desktop FluencyCoach software provides DAF and FAF on a Windows computer.
- Fluency Enhancer
The Fluency Enhancer is an iPod size anti-stuttering device providing DAF and octave-scale FAF pitch-shifting. It is intended to be used with stuttering therapy, and the price includes such stuttering therapy with the National Center for Stuttering. The device can be used with a full-size headset, miniature cellphone earsets, or Bluetooth wireless earsets. The device also plugs into telephones.
- Fluency Master
The Fluency Master is a hearing-aid size anti-stuttering device. The device picks up your vocal fold vibrations via a microphone contacting your skin. It ampliﬁes your vocal tone and provides the sound to your ear. A study of 21 adult stutterers found that stuttering in conversations was reduced on average 14%.20
- Fluency Pal
Fluency Pal is DAF software that runs on Nokia cellphones.
- Kay Elemetrics Facilitator
The Facilitator provides DAF, metronome, and white noise masking. The device is portable (weighing about 12 ounces) and includes a lapel microphone and headphones.
- SmallTalk, School DAF
Casa Futura Technologies manufactures the SmallTalk, School DAF, and other anti-stuttering devices. All are iPod size. All provide DAF; most provide octave scale pitch-shifting FAF; and some models have MAF manual masking buttons. All can be used monaurally (one ear) or binaurally (two ears). The devices can be used with full-size headsets, miniature cellphone earsets, Bluetooth wireless cellphone earsets, or wirelessly with hearing aids. The frequency range is 60-5000 Hz. Anti-background noise features include noise-canceling microphones, push-to-talk buttons, high-frequency filters, and voice activation. Some models plug into telephones.
- Nine severe adult stutterers used Casa Futura Technologies School DAF devices, without speech therapy, for an average of thirty minutes per day. The devices initially reduced stuttering about 70%, and no statistically significant change in effectiveness was seen after three months. After three months the subjects had 55% carryover fluency (when speaking without the devices).14 A second study also found 55% carryover fluency one year after using a Casa Futura Technologies School DAF device with speech therapy.15
- Two studies investigated Casa Futura Technologies DAF/FAF anti-stuttering devices in high stress speaking situations. Seven adults in the first study and nine adults in the second study made telephone calls to local businesses. The first study found an 80% reduction in stuttering;16 the second study found a 60% reduction in stuttering. 17
- A Casa Futura Technologies DAF/FAF anti-stuttering device was more than twice as effective when compared to a SpeechEasy anti-stuttering device.18
- In a study of stutterers reading aloud in a speech clinic, a Casa Futura Technologies DAF/FAF anti-stuttering device reduced stuttering about 70%. About 17% of words were stuttered without the device (NAF). Stuttered words with DAF or FAF varied between 2% and 8%.19
SpeechEasy anti-stuttering devices look like hearing aids and provide DAF and frequency-shifting FAF (adding or subtracting 500, 1000, or 2000 Hz). The frequency range is 200-8000 Hz.21 The devices are monaural (one ear). Anti-background noise features include: high-frequency filter, voice activation (EVAT), dynamic expansion (INAS).
- Thirteen adult stutterers were tested using the SpeechEasy anti-stuttering device in a speech clinic for reading, monologue, and conversation. On average stuttering was reduced 36%. The subjects were then given speech therapy and the combination of therapy and the device reduced stuttering 53%.22
- Nine stutterers used SpeechEasy anti-stuttering devices about seven hours per day. Their fluency was measured after four months and after twelve months.23 The delay was set at 60 milliseconds and the FAF at 500 Hz up. The subjects received brief speech therapy. The devices reduced stuttered syllables about 80%. The users had no statistically significant carryover fluency.
- A four-month long-term study24 investigated the effects of SpeechEasy devices in eleven adult subjects. Three conditions were investigated: reading aloud, conversation with an experimenter, and asking a question to a stranger. (In other words, a low-stress speaking task, a medium-stress speaking task, and high-stress speaking task.) Speech samples were collected before using the SpeechEasy device, during the four-month period when the device was used, and after the four-month trial (not using the device). The only statistically significant effect was seen in the reading task, in which stuttering was reduced from about 17% of syllables to about 8% of syllables when using the SpeechEasy device. There appeared to be a carryover effect in the reading task but it wasn't statistically significant. In the conversation task, stuttering was reduced from about 20% to about 19% with the device, and returned to about 20% after using the device. In the question task, stuttering was reduced from about 26% to about 23% when using the device, and about 22% after using the device. The effects in the latter two speaking tasks were not statistically significant. These results suggest that stuttering increases in higher stress speaking tasks, and that the SpeechEasy is most effective in low-stress speaking tasks.
- A three-year long-term study25 raised questions about whether SpeechEasy devices "wear off" or lost effectiveness over time. Of nineteen subjects, twelve (63%) had excellent initial results, with 1% or less stuttering. Two subjects (11%) experienced no improvement in their speech. On average, the devices reduced stuttering initially about 75%. Nine subjects purchased the devices (additionally, two subjects purchased and then returned the devices). The nine who purchased were re-evaluated an average of seven months later. Four continued to have excellent speech (1% or less stuttering). One person who had only good results initially now had excellent results (an improvement over six months). One person who had excellent results initially now had only good results. Two others had speech worse than before using the device. On average, the devices now reduced stuttering about 57%. Six subjects returned for a second follow-up, on average eighteen months after purchasing the devices. Two subjects were stuttering about as much as before they purchased the device. The other four subjects were worse. On average, the device now increased stuttering about 50%. Five subjects were tested at a third follow-up, on average after 30 months using the device. One subject had better speech after 30 months than before using the device (his stuttering dropped from 30% to 17%). Two subjects appear to have speech about the same as before using the device. One subject had moderately worse speech, and one had substantially worse speech (stuttering went from 2% to 9%). Adding the three additional subjects who were tested at the second follow-up but not the third follow-up, this study raises questions of whether five of eight SpeechEasy users had worse stuttering after long-term use of the device, two had speech about the same as before using the device, and one had improved speech.
- Speech Monitor
DAF/FAF software for Windows computers.
The StutterFree anti-stuttering device uses a special microphone to pick up the user's vocal fold vibration (phonation) and provide this sound to the user's ears. The device is iPod size and is used with small earphones.
The VoiceAmp VA 601 is an iPod size anti-stuttering device producing DAF and frequency-shifting FAF (adding or subtracting 500, 1000, or 2000 Hz). It's used with miniature cellphone earsets.
- Note 1: 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, Volume 40, 832-847, August 1997.
- Note 2: 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.
- Note 3: Dewar, A., Dewar, A.D., Austin, W.T.S., Brash, H.M. (1979) "The Long Term Use of an Automatically Triggered Auditory Feedback Masking Device in the Treatment of Stammering," British Journal of Disorders of Communication, vol. 14, no. 3.
- Note 4: 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.
- Note 5: 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.
- Note 6: 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.
- Note 7: Armson,J., Foote,S., Witt,C., Kalinowski,J., & Stuart,A. (1997). "Effect of frequency altered feedback and audience size on stuttering." European Journal of Disorders of Communication, 32, 359–366.
- Note 8: Hargrave,S., Kalinowski,J., Stuart,A., Armson,J., & ones,K.(1994). "Effect of frequency altered feedback on stuttering frequency at normal and fast speech rates." Journal of Speech and Hearing Research, 37, 1313–1319.
- Note 9: Kalinowski,J., Stuart,A., Sark,S., & Armson,J. (1996). "Stuttering amelioration at various auditory feedback delays and speech rates." European Journal of Disorders of Communication, 31, 259–269.
- Note 10: Kalinowski,J., Stuart,A., Wamsley,L., & Rastatter,M.P. (1999). Effects of monitoring condition and frequency-altered feedback on stuttering frequency. Journal of Speech, Language, and Hearing Research, 42,1347–1354.
- Note 11: Wu, Joseph, Gerald Maguire, Glyndon Riley, “A positron emission tomography 18-Fdeoxyglucose study of developmental stuttering,” in Cognitive Neuroscience and Neuropsychology, Vol. 6 No. 3, February 1995, p.501-503. Wu, J.C., Maguire, G., Riley, G., Fallon, J., LaCasse, L., Chin, S., Klein, E., Tang, C., Cadwell, S., Lottenberg, S. (1995). "A positron emission tomography 18Fdeoxyglucose study of developmental stuttering." Neuroreport, 6, 501-505. Fox, PT, Ingham, RJ, Ingham, JC, et al., "A PET study of the neural systems of stuttering," Nature, vol. 382, July 11 1996, 158-162. Wu, J.C., Maguire, G., Riley, G.D., in Speech Production: Motor Control, Brain Research and Fluency Disorders, edited by W. Hulstijn, H.F.M. Peters, and P.H.H.M. Van Lieshout, Amsterdam: Elsevier, 1997. Braun, A.R., Varga, M., Stager, S., Schulz, G., Selbie, S., Maisog, J.M., Carsom, R.E., Ludlow, C.L. "Atypical Lateralization of Hemispehral Activity in Developmental Stuttering: An H215O Positron Emission Tomography Study," in Speech Production: Motor Control, Brain Re-search and Fluency Disorders, edited by W. Hulstijn, H.F.M. Peters, and P.H.H.M. Van Lieshout, Amsterdam: Elsevier, 1997. Ingham R.J., Fox, P.T., Ingham, J.C.. "A H215O Positron Emission Tomography (PET) Study On Adults Who Stutter: Findings and Implications," in Speech Production: Motor Control, Brain Research and Fluency Disorders, edited by W. Hulstijn, H.F.M. Peters, and P.H.H.M. Van Lieshout, Amsterdam: Elsevier, 1997.
- Note 12: Elman, J. (1981). “Effects of frequency-shifted feedback on the pitch of vocal productions,” Journal of the Acoustical Society of America, 70 (1). Burnett, T.A., Senner, J.E., and Larson, C.R. (1997). “Voice F0 responses to pitch-shifted auditory feedback: A preliminary study,” J. Voice, 11, 202-211. Burnett, T.A., Freedland, M.B., Larson, C.R., Hain, T.C. (1998). “Voice F0 responses to manipulations in pitch feedback,” Journal Acous-tical Society of America, 103 (6) June 1998.
- Note 13: Stuart, A., Kalinowski, J., and Rastatter, M. (1997). Effect of monaural and binaural altered auditory feedback on stuttering frequency, Journal of the Acoustical Society of America, 111, 2237-2241.
- Note 14: Van Borsel, J., Reunes, G., and Van den Bergh, N. (2003). Delayed auditory feedback in the treatment of stuttering: clients as consumers, International Journal of Language and Communication Disorders, 2003, Vol. 38, No. 2, 119-129.
- Note 15: 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.
- Note 16: Brenaut, L., Morrison, S., Kalinowski, J., Armson, J., Stuart, A. (1995). "Effect of Altered Auditory Feedback on Stuttering During Telephone Use." Poster session, American Speech-Language Hearing Association convention, from Dalhousie University, Halifax, Nova Scotia, Canada, 1995.
- Note 17: Zimmerman, S., Kalinowski, J., Stuart, A., Rastatter, M. (1997). "Effect of Altered Auditory Feedback on People Who Stutter During Scripted Telephone Conversations." Journal of Speech, Language, and Hearing Research, Vol. 40, 1130-1134, October 1997.
- Note 18: Hyde, L. (2003). Comparison of the SpeechEasy and Casa Futura/Jabra fluency devices, presentation to the Canadian Association of Persons who Stutter conference, August 2003.
- Note 19: Grosser, J., Natke, U., Langefeld, S., & Kalveram, K. Th. (2001) Reduction in stuttering by delayed and frequency shifted auditory feedback: Effects of adaptation and sex differences. In H. G. Bosshardt, J. S. Yaruss & H. F. M. Peters (Eds.), Fluency Disorders: Theory, Research, Treatment and Self-help. Proceedings of the Third World Congress of Fluency Disorders in Nyborg, Denmark. Nijmegen: Nijmegen University Press, 422-426. Abstract, Full version (PDF, 27 kb).
- Note 20: Webster, Ronald. "Manipulation of Vocal Tone: Implications For Stuttering," in Speech Motor Controls and Stuttering, ed. Peters, Hulstijn, and Starkweather, New York: Elsevier, 1991.]
- Note 21: Stuart, A., Xia, S., Jiang, Y., Jiang, T., Kalinowski, J., Rastatter, M. "Self-contained in-the-ear device to deliver altered auditory feedback: applications for stuttering," Annals of Biomedical Engineering, 31, 233-237, 2003.
- Note 22: Armson, J., Keifte, M., Mason, J., De Croos, D. "The effect of SpeechEasy on stuttering frequency in laboratory condition," Journal of Fluency Disorders 31 (2006) 137-152.
- Note 23: Stuart, A., Kalinowski, J., Rastatter, M., Saltuklaroglu, T., Dayalu, V. "Investigations of the impact of altered auditory feedback in-the-ear devices on the speech of people who stutter: initial fitting and 4-month follow-up," International Journal of Language and Communication Disorders, 2004, 39:1, 93-113. Stuart, A., Kalinowski, J., Saltuklaroglu, T., Guntupalli, V. "Investigations of the impact of altered auditory feedback in-the-ear devices on the speech of people who stutter: One-year follow-up," Disability and Rehabilitation, 2006. 1-9.
- Note 24: Pollard, R., Ellis, J.. Ramig, P., Finan, D. A longitudinal study of the effects of the SpeechEasy device in naturalistic environments. presentation to American Speech-Language Hearing Association convention, November 2006; an updated study was presented at the International Stuttering Association conference, May 2007.
- Note 25: Runyan, C., Runyan, Sara. "The Speech Easy: A Two Year Study," presentation at the American Speech-Language Hearing Association convention, November 2005. A follow-up study was presented at the American Speech-Language Hearing Association convention, November 2006.