Delayed Auditory Feedback

             Delayed Auditory Feedback, nicknamed DAF, is sometimes helpful for older children, teens and adults who stutter. DAF is easily accessible now as a mobile app. So, I think it’s important to talk about it. DAF is when a speaker does not hear her own voice in real time, but instead, hears it after a teeny tiny delay. Here’s a more scientific description:

            “Briefly, when speech is fed back to a speaker via earphones at 75 to 100 milliseconds delay (one tenth of a second), the speaker will automatically (passively) slow their rate of utterance, flatten their intonation, prolong their words and/or raise their speech volume to cope with the competing signal…

            “The alteration in speech prosody will often inhibit the stuttering response. Unfortunately this does not carry-over very well because the DAF is not paired to the stuttering specifically but to the speech signal in general. It is therefore difficult to maintain this new speech pattern without the DAF/echo-present…

            “The effects of speaking in the presence of your own delayed speech signal remains the single most efficient, immediate and initially passive fluency evoking stimuli available.”   A therapy program may include DAF to help establish greater fluency, then arrange for it to “be gradually reduced so that the individual is speaking with his own internal controls.” [1]

              Many of my clients have tried DAF.  In the late 1990s, I helped several of them obtain free DAF for phone use. In 2001, I discovered the Casa Futura School DAF in a catalogue and bought one. It cost almost $300 (and another $27.00 when a student stepped on the headset).  In 2008, I bought two more devices. It was the most affordable DAF at the time. Then, in 2011, SPEECH4GOOD [2] put DAF into a mobile application. One of my clients purchased it this spring for under $10! Version 3.0 launched this month. These dramatic changes in price and availability prompted me to re-examine the role of DAF for speech language pathologists who treat stuttering.

            My own use of DAF has to do with the nature of my business.  My clients tend not to follow through with the rigorous expectations of speech therapy, so, I find myself writing fewer lesson plans and more educational/problem-solving memos.  That means spending a lot of time learning about issues associated with fluency: concomitant disorders, therapy options, parenting, child development, social communication, literacy, and the ever changing landscape of public education. So, when new student responded particularly well to DAF, I had another reason to re-examine this option.

            Let’s begin with a study published this year.  It found that fluent adults responded to DAF with an increase in stutter-like dysfluencies and sound errors, and, the adults fell roughly into two groups. Adults who experienced the least amount speech disruption with DAF were given the label “low responders.” The authors of the study hypothesized that these low responders “have better developed speech motor skills…[which enabled] fluent speech under the DAF perturbation by using more accurate feedfoward control [3]…[and also] that low responders could be less dependent on auditory feedback…” The other group of adults were greatly affected by DAF.  This second group of adults experienced much more speech disruption and so they were labeled “high responders”. “In contrast, high responders have a high dependency on auditory feedback to maintain fluency under typical speaking conditions…” In the larger scheme of things, these results add “…to the accumulating findings that motor-phonetic encoding involves auditory-to-motor integration.”[4] Perhaps we can hypothesize that our clients respond differently to DAF because of differences in auditory-to-motor integration. I propose that research such as this justifies the inclusion of DAF as an option in speech therapy.

            In truth, the use of DAF for persons who stutter is a topic of contentious debate. I kind of enjoy heated arguments in professional journals. I’m curious to read how deeply held disagreements are thinly disguised as polite discussions. Also, controversy reveals fascinating details. As I understand it, one side of this controversy over DAF declares that decades of evidence prove DAF has a powerful effect on stuttering.[5] The opposing view challenges this research.[6]  The challenge is not trivial.

             The issue of legitimacy appears in a fascinating article about Lionel Logue, the speech therapist portrayed in The King’s Speech.[7]  Highly respected clinicians of the early 20th century were unsuccessful in helping Prince Albert, Duke of York, manage his stuttering. On the other hand, Lionel Logue, with less formal education, was portrayed as experienced, persistent, and successful.

            “Logue’s therapy methods were typical of those used by other clinicians of his time…emphasizing diaphragmatic breathing…muscle relaxation…methods that provided King Albert with a sense of his own fluency [including] masking the feedback the king received from his own voice, …singing through blocks…counseling…[and nurturing] the confidence that he could, with hard work, within the proper therapeutic regimen, stutter less.” [8]

            “To achieve legitimacy, today’s practitioners are encouraged to select methods that have been shown to be efficacious when studied using evidence-based methods (ASHA 2011). For therapies that have not been scrutinized by evidence-based systematic reviews, today’s clinicians are sometimes asked to provide their own documentation of therapy progress, using carefully controlled, objective methods…” [9]

            By now, I’ve left DAF  by the wayside and turned my attention to Evidence Based Practice, commonly known as EBP. For any reader still with me, this will be a short and productive digression. I cracked open a textbook to a chapter about the role of evidence in stuttering treatment.  Let’s begin with a definition. In EBP, “ evidence refers to research findings, and the goal of clinical practice is to find and implement the treatment that represents the best combination of information from three sources : (1) research (i.e., evidence), (2) physician or clinician expertise, and (3) patient or client preferences.” [10]

            I learned about four levels of evidence quality and how, apparently, the only legitimate evidence in the field of stuttering was provided by a few literature summaries, prepared by a few authors, and justified only a few therapeutic approaches. I read about clinician bias and insufficient client input. There appeared to be wholesale disregard for whole lot of research.  I like reading my ASHA journals yet the article discredited such an approach, stating   “reading individual research reports should actually be a last resort for practitioners.” [11]  So, I respectfully disagree. Journal publications provide more than experimental data. They include brief historical reviews, theoretical hypotheses, and intriguing discussion. They illustrate ways to think about complex issues.

            Thankfully, this book chapter ended with some suggestions. “For current stuttering treatments in particular, because the highest levels of evidence hierarchy (systems, synopses, and even multiple meta-analyses and systematic reviews) are not yet widely available, it becomes the responsibility of the clinician to carefully assess the effectiveness of the selected treatment with each client.” [12] EBP can focus on “one clinician-client pair at a time” . Treatment should be “directed toward relieving the client’s ‘source of complaint’” and  “…the ‘most critical components of stuttering treatment outcome evaluation…might be the self-judgments or self-measurements made by the speakers themselves.’”   We can apply this guidance to the use of DAF. [13]

            Now that DAF is widely available as an app, I feel that SLP’s should educate the public about how it might be helpful.  It could be a way for clients to generalize communication goals outside the speech clinic. Apps may be a way for clients to make the self-judgments and self-measurements necessary in a EBP approach to communication change. I hope SLPs will take advantage of this technology, even though it will require some creativity within the ideals of EBP .



            I finished this article feeling somewhat incompetent. Has my profession failed to keep up with recent changes in health care standards?  My mind cleared  after reading an article in the newspaper about the humanities in  modern day higher education. College is becoming a narrowly focused job training program rather than an opportunity for high level, broad based education. “The tragedy of the humanities is that it has become cordoned off: viewed as separate, arcane, and indulgent, instead of something that undergirds the other parts of life. Maybe instead of trying to steer students back to humanities degrees, we should be rethinking the way we teach humanities in general. We could be foisting those thinking skills on everyone, a bit.”[14]  I could definitely relate! An SLP draws from a wide range of knowledge and skills.

           While I commend the profession of speech language pathology for staying grounded in science, speech/language therapy requires a generous amount of "humanness". Think about the personal manner of your child's pediatrician., or even the customer service you received while dining out?  I feel the best of these relationships are based on something almost invisible yet tangible.  The therapeutic alliance is similar for me - invisible yet essential.   Which leads me to my next topic: mindfulness. But first, I'll visit an art museum and remind myself  that life is more than big data.

[1] Richard M. Merson (2003) “Auditory Sidetone and the Management of Stuttering: From Wollensak to SpeechEasy” http://www.mnsu.edu/comdis/isad6/papers/merson6.html
[3] Judith V. Butler (11/7/10) DIVA http://butlerspeechtherapy.blogspot.com/2010/11/diva.html, italics mine
[4] H.C. Chon, et. al. (2013) Individual Variability in Delayed Auditory Feedback Effects on Speech Fluency and Rate in Normally Fluent Adults. Journal of Speech, Language, and Hearing Research, Vol. 56, p. 500 for all quotes
[5] J. Kalinowski & V.K. Guntupalli (2007) On the Importance of Scientific Rhetoric in Stuttering: A Reply to Finn, Bothe, and Bramlett (2005), American Journal of Speech-Language Pathology, Vol. 16, 69-76.
[6] P. Finn, et. al. (2005) Science and Pseudoscience in Communication Disorders: Criteria and Applications, American Journal of Speech-Language Pathology, Vol. 14, 172-186.
[7] Judith Felson Duchan (2012) Historical and Cultural Influences on Establishing Professional Legitimacy: A Case Example from Lionel Logue. American Journal of Speech Language Pathology, Vol. 21, 387-396.
[8] Ibid. p. 391
[9] Ibid. p. 393
[10] A.K. Bothe, et. al. (2010) The Roles of Evidence and Other Information in Stuttering Treatment, in B. Guitar & R.. MCCauley (eds.) Treatment of Stuttering: Established and Emerging Interventions, (pp. 343-354).Baltimore, MD: Lippincott Williams & Wilkins. p. 344
[11] Ibid. p. 349
[12] Ibid. p. 352
[13] Ibid. remaining quotes from p. 351
[14] Joanna Weiss (June 16, 2013) Humanities at Risk: Let’s rethink the way we teach college students. The Boston Sunday Globe, p.K8
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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.