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Electronic fluency devices (also known as assistive devices, electronic aids, altered auditory feedback devices and altered feedback devices) are electronic devices intended to improve the fluency of persons who stutter. Most electronic fluency devices change the sound of the user's voice in his or her ear.



Electronic fluency devices can be divided into two basic categories.

  • Computerized feedback devices provide feedback on the physiological control of respiration and phonation, including loudness, vocal intensity and breathing patterns.[1]
  • Altered auditory feedback (AAF) devices alter the speech signal so that speakers hear their voices differently.[2]

Computerized feedback devicesEdit

Such devices use computer technology to increase control over breathing and phonation. A microphone gathers information about the stutterer’s speech and feedback is delivered on a computer screen. Measurements include intensity (loudness), voice quality, breathing patterns, and voicing strategies.[1] These programs are designed to train features related to prolonged speech, a treatment technique which is frequently used in stuttering therapy. No peer-reviewed studies have been published showing the effectiveness of commercial systems in a clinical context.[3]

Altered auditory feedback devicesEdit

Altered auditory feedback (AAF) such as singing, choral speaking, masking, delayed or frequency altered feefback[4][5] have been shown often to reduce stuttering.[2] Recent advances in technology have led to the development of devices that can be similar in size and appearance to a hearing aid, including in-the-ear and completely-in-the-canal models.[2][6]


White noise masking has been well-documented to reduce stuttering.[7][2][8] Clinic-based and portable devices have been developed to deliver masking (the Edinburgh Masker).[9] Interest in masking reduced during the 1980s as a result of studies finding delayed auditory feedback and frequency altered feedback were more effective in reducing stuttering.[2][7]

Delayed auditory feedbackEdit

The effect of delayed auditory feedback (DAF) in reducing stuttering has been noted since the 1950s.[10][11] 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.[2] In stutterers, DAF may produce slow, prolonged but fluent speech. In the 1960s to 1980s, DAF was mainly used to train prolongation and fluency. As the stutterer masters fluent speech skills at a slow speaking rate, the delay is reduced in stages, gradually increasing speaking rate, until the person can speak fluently at a normal speaking rate.[12][13] It was not until the 1990s that research began to focus on DAF in isolation. Recent studies have moved from longer delays to shorter delays in the 50 millisecond to 75 millisecond range, and have found that speakers can maintain fast rates and achieve increased fluency at these delays.[2][7][14][15] Delayed auditory feedback presented binaurally (i.e. in both ears) is more effective than that presented in monaurally, or in one ear only.[16]

Frequency-altered feedbackEdit

Pitch-shifting frequency-altered auditory feedback (FAF) changes the pitch at which the user hears his or her voice. Varying pitch from quarter, half or full octave shift typically results in 55-74% decreases stuttering in short reading tasks.[7][15][17][18] Individuals differ as to direction and extent of the pitch shift required to maximally reduce stuttering.[19] In studies that gave longer exposure to FAF and used more meaningful daily life tasks such as generating a monologue, only some participants experienced a reduction in stuttering.[20][21] While there is some contradictory evidence, most studies have noted that DAF is more powerful than FAF in reducing stuttering.[2] FAF is, like DAF, more effective when presented binaurally.[16]


Studies have shown that altered auditory feedback (including delayed auditory feedback, frequency altered feedback) can reduce stuttering by 40 to 80 per cent in reading tasks.[22][2][23] Laboratory studies suggest that reductions in stuttering with an electronic fluency device can occur without a reduced speech rate, and that speech naturalness is often enhanced with AAF.[20][6] Purchasers of an AAF device reported that the device reduced stuttering and had a positive effect on their conversational speech and telephone use,[24] though they were more difficult to use in noisy settings as the device amplifies all voices and sounds.[25]

The effects of altered feedback are highly individualistic, with some obtaining considerable increases in fluency, while others receive little or no benefit.[2][20][21][26] The longterm effects of altered feedback are unclear: there is some limited experimental data that in some speakers the effect of AAF may fade after a few minutes of exposure.[21] Anecdotal reports suggest that over time users receive continued but lessened effects from their device,[27][25] however, one study has shown continued overall reductions in stuttering after a year of daily use.[26] Others found carryover fluency, i.e., the reduction in stuttering after the stutterer removes the device,[22][28] while others do not.[6][26]

Critics have noted weaknesses in many of the studies measuring the efficacy of electronic fluency devices,[2] and have criticized their high-profile promotion in the media as inappropriate given the lack of scientific evidence for their effectiveness.[13][29][30] In particular, there are no published studies on the effect of the AAF on conversational speech: studies have mainly examined the effect of AAF on short oral reading tasks, while a few have studied the giving of a monologue that is usually short in duration.[2] A review of stuttering treatments noted that none of the treatment studies on altered auditory feedback met the criteria for experimental quality.[31]

Use with childrenEdit

There is little experimental evaluation of the therapeutic effect of AAF on children who stutter: one study noted that effects of FAF were less in children than adults.[32] Given the lack of evidence of its effectiveness, as well as concerns about the impact of altered feedback on developing speech and language systems, some authors have expressed the view that the use of an AAF with children would be unethical.[2]

Causes of altered auditory feedback effectsEdit

The precise reasons for the fluency-inducing effects of AAF in stutterers are unknown. Early investigators suggested that those who stutter had an abnormal speech–auditory feedback loop that was corrected or bypassed while speaking under DAF.[6] Later researchers proposed increased fluency was actually caused by the changes in speech production, including slower speech rates, higher pitches and increased loudness, rather than the AAF per se.[33][34] However, subsequent studies have noted that increased fluency occurred in some stutterers at normal and fast rates using DAF.[35][34] Some suggest that stuttering is caused by defective auditory processing, and that AAF helps to correct the misperceived rhythmic structure of speech.[36] It has been shown that some stutterers have noted that have atypical auditory anatomy and that DAF improved fluency in these stutterers but not in those with typical anatomy.[37] However, positron emission tomography studies on choral reading in stutterers suggest that AAF also made changes in motor and speech production areas of the brain, as well as the auditory processing areas. Choral reading reduced the overactivity in motor areas that is found with stuttered reading, and largely reversed the left-hemisphere based auditory-system and speech production system underactivation.[38][39] Noting that the effects of altered feedback vary from person to person and can wear off over time, distraction has also been proposed has a possible cause of stuttering reduction with AAF.[40]


  • Ward, David (2006). Stuttering and Cluttering: Frameworks for understanding treatment, Hove and New York: Psychology Press.
  • Tim Saltuklaroglu; Joseph Kalinowski (2006). Stuttering, 173-4, Plural Publishing.
  1. 1.0 1.1 Ward (2006) p. 300
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 Lincoln M, Packman A, Onslow M (2006). Altered auditory feedback and the treatment of stuttering: a review. J Fluency Disord 31 (2): 71–89.
  3. Ingham RJ, Kilgo M, Ingham JC, Moglia R, Belknap H, Sanchez T (2001). Evaluation of a stuttering treatment based on reduction of short phonation intervals. J. Speech Lang. Hear. Res. 44 (6): 1229–44.
  4. Ward (2006) p. 293
  5. Saltuklaroglu and Kalinowski (2006) p. 173-4
  6. 6.0 6.1 6.2 6.3 Stuart A, Kalinowski J, Rastatter M, Saltuklaroglu T, Dayalu V (2004). 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 & communication disorders / Royal College of Speech & Language Therapists 39 (1): 93–113.
  7. 7.0 7.1 7.2 7.3 Kalinowski J, Armson J, Roland-Mieszkowski M, Stuart A, Gracco VL (1993). Effects of alterations in auditory feedback and speech rate on stuttering frequency. Language and speech 36 ( Pt 1): 1–16.
  8. Stager SV, Denman DW, Ludlow CL (1997). Modifications in aerodynamic variables by persons who stutter under fluency-evoking conditions. J. Speech Lang. Hear. Res. 40 (4): 832–47.
  9. Dewar, A, & Dewar, AD (1979). The long-term use of an automatically triggered auditory feedback-masking device in the treatment of stammering. British Journal of Disorders of Communication 14: 219–229.
  10. Ward, p. 48
  11. Saltuklaroglu and Kalinowski (2006), p. 239
  12. Ward, p. 49
  13. 13.0 13.1 Bothe AK, Finn P, Bramlett RE (2007). Pseudoscience and the SpeechEasy: Reply to Kalinowski, Saltuklaroglu, Stuart, and Guntupalli (2007). American Journal of Speech-Language Pathology 16: 77–83.
  14. Kalinowski J, Stuart A (1996). Stuttering amelioration at various auditory feedback delays and speech rates. European journal of disorders of communication : the journal of the College of Speech and Language Therapists, London 31 (3): 259–69.
  15. 15.0 15.1 Zimmerman S, Kalinowski J, Stuart A, Rastatter M (1997). Effect of altered auditory feedback on people who stutter during scripted telephone conversations. J. Speech Lang. Hear. Res. 40 (5): 1130–4.
  16. 16.0 16.1 Stuart A, Kalinowski J, Rastatter M (1997). Effect of monaural and binaural altered auditory feedback on stuttering frequency. Journal of the Acoustical Society of America 111: 2237–41.
  17. 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 : the journal of the College of Speech and Language Therapists, London 32 (3): 359–66.
  18. Kalinowski J, Stuart A, Wamsley L, Rastatter MP (1999). Effects of monitoring condition and frequency-altered feedback on stuttering frequency. J. Speech Lang. Hear. Res. 42 (6): 1347–54.
  19. Hargrave S, Kalinowski J, Stuart A, Armson J, Jones K (1994). Effect of frequency-altered feedback on stuttering frequency at normal and fast speech rates. Journal of speech and hearing research 37 (6): 1313–9.
  20. 20.0 20.1 20.2 Ingham RJ, Moglia RA, Frank P, Ingham JC, Cordes AK (1997). Experimental investigation of the effects of frequency-altered auditory feedback on the speech of adults who stutter. J. Speech Lang. Hear. Res. 40 (2): 361–72.
  21. 21.0 21.1 21.2 Armson J, Stuart A (1998). Effect of extended exposure to frequency-altered feedback on stuttering during reading and monologue. J. Speech Lang. Hear. Res. 41 (3): 479–90.
  22. 22.0 22.1 Van Borsel J, Reunes G, Van den Bergh N (2003). Delayed auditory feedback in the treatment of stuttering: clients as consumers. International journal of language & communication disorders / Royal College of Speech & Language Therapists 38 (2): 119–29.
  23. Ward (2006), p. 299
  24. Kalinowski J, Guntupalli VK, Stuart A, Saltuklaroglu T (2004). Self-reported efficacy of an ear-level prosthetic device that delivers altered auditory feedback for the management of stuttering. Int J Rehabil Res 27 (2): 167–70.
  25. 25.0 25.1 Davis, Robert (2004-10-18), "Those who stutter find hope", USA Today, 
  26. 26.0 26.1 26.2 Stuart A, Kalinowski J, Saltuklaroglu T, Guntupalli VK (2006). 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 28 (12): 757–65.
  27. Ward (2006), p. 296, 298
  28. Radford NT, Tanguma J, Gonzalez M, Nericcio MA, Newman DG (2005). A case study of mediated learning, delayed auditory feedback, and motor repatterning to reduce stuttering. Perceptual and motor skills 101 (1): 63–71.
  29. Finn P, Bothe AK, Bramlett RE (2005). Science and pseudoscience in communication disorders: criteria and applications. Am J Speech Lang Pathol 14 (3): 172–86.
  30. includeonly>Hidalgo, Jason. "Help for stutterers? Devices such as the SpeechEasy are growing popular due to exposure on shows like “Oprah,” but experts say they may not be the miracle cures people expect", Reno Gazette-Journal, 2004-01-26. Retrieved on 2007-12-02.
  31. Bothe AK, Davidow JH, Bramlett RE, Ingham RJ (2006). Stuttering Treatment Research 1970-2005: I. Systematic Review Incorporating Trial Quality Assessment of Behavioral, Cognitive, and Related Approaches. American Journal of Speech-Language Pathology 15: 321–341.
  32. Howell, P, Sackin, S, Williams, R (1999). Differential effects of frequency-shifted feedback between child and adult stutterers. Journal of Fluency Disorders 24 (2): 127–136.
  33. Ward, 2006, p. 50
  34. 34.0 34.1 Sparks G, Grant DE, Millay K, Walker-Batson D, Hynan LS (2002). The effect of fast speech rate on stuttering frequency during delayed auditory feedback. J Fluency Disord 27 (3): 187–200; quiz 200–1, III.
  35. Kalinowski J, Stuart A (1996). Stuttering amelioration at various auditory feedback delays and speech rates. Eur J Disord Commun 31 (3): 259–69.
  36. Harrington J (1988). Stuttering, delayed auditory feedback, and linguistic rhythm. J Speech Hear Res 31 (1): 36–47.
  37. Foundas AL, Bollich AM, Feldman J, et al (2004). Aberrant auditory processing and atypical planum temporale in developmental stuttering. Neurology 63 (9): 1640–6.
  38. Wu JC, Maguire G, Riley G, et al (1995). A positron emission tomography [18F]deoxyglucose study of developmental stuttering. Neuroreport 6 (3): 501–5.
  39. Fox PT, Ingham RJ, Ingham JC, et al (1996). A PET study of the neural systems of stuttering. Nature 382 (6587): 158–61.
  40. Ward, 2006, p. 57

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