Technology for Stuttering Treatment
- Category: Stuttering Treatment
- Altered auditory feedback (AAF) for inducing speech motor changes and correcting the abnormal auditory processing associated with stuttering.
- Delayed Auditory Feedback (DAF)
- Frequency-Altered Auditory Feedback (FAF)
- Other Types of Altered Auditory Feedback
- Technical Aspects of Altered Auditory Feedback
- Effectiveness of AAF Devices in Stressful Speaking Situations
- Long-Term Effects of AAF Devices
- Effects of Speech Therapy with Portable AAF Devices
- Summary of SpeechEasy Studies
- Summary of Casa Futura Technologies Studies
- Biofeedback for improving awareness and control of speech motor processes.
- Software for treating psychological disorders such as social anxiety.
Technology can improve the speech of stutterers in three ways:
- The technology makes another stuttering therapy more effective, such as increased fluency, more natural speech quality, preventing relapse over time, reducing therapy time or expense, or enabling speech-language pathologists (SLPs) without specialized training in fluency disorders to treat stuttering effectively.
- The technology treats an aspect of stuttering untouched by other therapies. This criterion assumes that more than one factor contributes to stuttering, i.e., that there is no single cause or cure for stuttering.
- The technology takes stuttering therapy out of the speech clinic and into situations of daily life. This is important because stuttering is a stress-related disorder. Many stuttering therapies can make stutterers speak fluently in a speech clinic, but fewer stuttering therapies are effective in stressful speaking situations.
Altering how people hear their voices, called altered auditory feedback (AAF), changes how they speak and can improve the fluency of stutterers. Lincoln  reviewed seventeen studies of AAF devices and concluded,
From the above review of experimental studies we can confidently conclude that in the laboratory, clinic, or classroom AAF will result in reduced stuttering during oral reading for most people who stutter.
The review found reductions of stuttering in the range 40-85%, including stressful speaking situations. Long-term studies (up to one year) didn't find adaptation or "wearing off" of effectiveness, and found that one device (the School DAF) trained carryover fluency (when users weren't wearing the device).
In 1965 Israel Goldiamond discovered that when stutterers hear their voices in headphones delayed a fraction of a second, called delayed auditory feedback (DAF), they speak slowly and fluently. This discovery led to the development in the 1970s of prolonged speech stuttering therapy (also known as fluency shaping), which is now considered to be the most effective treatment for adult and childhood stuttering  .
DAF is widely used by SLPs in prolonged speech stuttering therapy to induce a slower speaking rate with stretched vowels and each syllable held for an equal length of time. The protocol is to start with a delay of about 200 milliseconds (ms) to induce the stutterer to stretch each syllable about one second, or five times slower than normal speech. Therapy begins with single sounds, words, and short phrases; and then works towards long conversations. When the stutterer is fluent at this speaking rate the delay is reduced to about 100 ms and the stutterer's speaking rate increases to one-half second per syllable. When the stutterer is fluent at this speaking rate the delay is then reduced to about 75 milliseconds and the stutterer's speaking rate increases to one-quarter second per syllable, which is a little slower than normal speech but sounds normal. When the stutterer is fluent at this speaking rate the DAF is then removed and the SLP and stutterer works on transferring this "slow-normal" fluent speech to speaking situations outside the speech clinic. Transfer may involve using a DAF device in stressful speaking situations, such as telephone calls, but then removing it for low-stress conversations. (The opposite doesn't work—practicing with a DAF in low-stress situations such as reading aloud doesn't transfer fluency to high-stress speaking situations.) DAF therapy reduces stuttering to under 2% and trains long-term carryover fluency, for both adults and children  .
Prolonged speech stuttering therapy can be done without DAF. No research has compared prolonged speech stuttering therapy with and without DAF. However, criterion #1 is met because thousands of SLPs without training in fluency disorders use DAF to provide prolonged speech stuttering therapy.
Before 1993 it was believed that "the functional variable in regard to the reduction of stuttering is not DAF, but prolonged speech, and the latter can be produced without reliance on a DAF machine."  Then in a seminal 1993 paper Kalinowski  found that DAF reduced stuttering at normal and faster-than-normal speaking rates, with increased speech naturalness. The research team wrote: "a slowed rate of speech is not a necessary antecedent for fluency improvement under conditions of altered auditory feedback." 
Underactive Auditory Processing
Also in the early 1990s the first brain imaging studies of stutterers were published. These studies associated stuttering with abnormally underactive auditory processing. This discovery was unexpected, but at the same time many other disorders, e.g., ADHD and language disorders, that appeared to have nothing to do with hearing were found to include an auditory processing abnormality. 
The central auditory processing area of our brains processes perceived sounds into useful information, such as words. Central auditory processing disorder (CAPD) is not a hearing disorder, i.e., a person with CAPD usually has nothing wrong with his or her ears. Other symptoms associated with CAPD include preferring to watch movies with the subtitles on, not being able to "pick up" foreign languages by ear, and not being able to understand what people are saying if there's background noise, such as at a loud party or outside on a windy day.
The auditory processing underactivity associated with stuttering is specifically in areas "thought to support self-monitoring of speech production."  Braun  found decreased activity in the area that integrates auditory and somatic sensation, suggesting that stutterers have an inability to compare what they hear themselves saying to how they feel their speech-production muscles moving. Stuttering may be one of many sensory integration disorders (SID) that originate in childhood. Perhaps childhood stuttering therapy should include exercises to train the child to listen to his speech and feel his muscles moving.
The Two Effects of DAF
DAF appears to have two effects:
- A long delay induces speech motor changes, i.e., induces fluent but abnormally slow and abnormal-sounding speech in stutterers, and requires training with an SLP and cognitive effort.
- A short delay stimulates the brain's auditory processing area and reduces stuttering (typically 70%  ) at normal speaking rates with normal-sounding speech, without training or speech therapy or cognitive effort.
Other forms of stuttering therapy don't't treat the abnormal auditory processing associated with stuttering, so DAF meets criterion #2.
The problems associated with DAF are due to confusing these two effects. Specifically, adaptation or "wearing off" of effectiveness seems to occur when stutterers set the delay at 100 ms or longer and then try to speak at a normal speaking rate. These individuals train themselves to ignore the DAF, possibly by further reducing their auditory processing activity. Over time their stuttering returns when using DAF, and in some cases their stuttering becomes worse. A stutterer who wishes to speak at a normal or fast speaking rate should set DAF at 50 ms; for a "slow-normal" speaking rate use 75 ms; and delays of 100 ms or longer should only be used for prolonged speech stuttering therapy (abnormally slow speech).
Many companies make portable DAF devices and iPhone apps to enable stutterers to use DAF outside of the clinical environment, so DAF meets criterion #3.
Planum Temporale Abnormality and DAF
The planum temporale (PT) is an anatomical feature in the auditory temporal brain region. Typically people have a larger PT on the left side of their brains, and smaller PT on the right side (leftward asymmetry). Two brain scan studies found that some stutterers have the opposite: their right PT is larger than their left PT (rightward asymmetry). The stutterers with this abnormal rightward asymmetry stuttered more severely and had significantly improved fluency with DAF compared to stutterers with the normal leftward asymmetry. 
With frequency-altered auditory feedback (FAF), a user hears the pitch of his or her voice shifted higher or lower. A quarter-octave pitch shift reduces stuttering about 35%. A half-octave pitch shift reduces stuttering 65-70%. A full-octave pitch shift reduces stuttering 70-75%. Combining DAF and FAF reduces stuttering about 80%. Upshifts and downshifts are equally effective in short-term studies. 
FAF induces speech motor changes, specifically vocal pitch changes.  Some stutterers raise their vocal pitch while others lower their vocal pitch when using FAF. No long-term studies have compared stutterers who raise their vocal pitch vs. stutterers who lower their vocal pitch. However, lower is likely better. A lower vocal pitch relaxes the user's breathing and vocal folds, when a higher vocal pitch increases speech motor activity. Speaking with tense breathing and vocal folds likely leads to increased stuttering over time, offsetting the gain in auditory processing and perhaps explaining the adaptation or "wearing off" of effectiveness and lack of carryover fluency found in some devices (see the section below for long-term studies).
FAF isn't used to improve existing stuttering therapies (criterion #1) but treats the auditory processing abnormality that other therapies don't address (criterion #2). Portable FAF devices and iPhone apps are available (criterion #3).
Other types of AAF include:
Synthesized sine waves synchronized to phonation, e.g., the Edinburgh Masker. Block  found that the device reduced stuttering about 50%. Dewar  found that the effectiveness didn't diminish over a period of six months. The volume in the users' ears was found to average 77.6 dBA, with a range of 70 to 85 dBA, i.e., safely below levels that could cause hearing damage. The hearing of five subjects was tested and no indications of hearing damage were found. Herb Goldberg, the American importer, reported, "I am in contact with over 500 people who use or have used the Masker. In most cases the end result is the person uses the device less and less as time passes due to less need for it." (Personal correspondence, September 9, 1994).
Bone-transmitted phonation, e.g., the Fluency Master. The device is similar to a hearing aid, except that the microphone is external to the hearing aid and is taped to the user's mastoid bone behind the ear. Webster  found a 14% reduction in stuttering in conversations without therapy.
Frequency-shifting, e.g., SpeechEasy and VoiceAmp. These devices add or subtract a fixed-frequency signal, e.g., 500 Hz, 1000 Hz, or 2000 Hz, to the vocal signal. No published research has investigated the effect of frequency-shifting on stuttering. Adding a fixed-frequency signal to a vocal signal makes the vocal signal sound higher in pitch; unlike pitch-shifting, lower-frequency vocal signals sound much higher in pitch (e.g., adding 500 Hz to 125 Hz vocal signal yields 625 Hz, shifting adult male phonation up more than two octaves) when higher-frequency vocal signals sound only a little higher in pitch (e.g., adding 500 Hz to a 5000 Hz vocal signal yields 5500 Hz, or only one-tenth octave higher). The result sounds like a robot on helium. Subtracting a fixed-frequency signal from a vocal signal cuts off (filters) the vocal signal below the fixed frequency plus the lower frequency limit of the receiver (e.g., subtracting a 500 Hz signal using a receiver that can't reproduce sound below 200 Hz removes all of the signal below 700 Hz). This reduces the volume of the speech signal and so is rarely used.
White noise masking. Kalinowski  compared white noise masking to DAF and to FAF, and found that 85 db white noise reduced stuttering 35%, when DAF reduced stuttering 55% and FAF reduced stuttering 62%. This supports the long-held view that stutterers are somewhat more fluent when they can't hear their voices, but shows that another mechanism makes DAF and FAF more effective.
Metronomes. Stager  found a metronome to be less effective than DAF.
Not all AAF devices are alike:
- Monaural vs. binaural. Stuart  found binaural (two ear) DAF/FAF devices to be 25% more effective than monaural (one ear) devices.
- Background noise. Microphones can be omnidirectional, which pick up background noise, or noise-canceling unidirectional, which reject background noise. Some devices are on all the time, whether the user is speaking or not, and so pick up background noise; other devices have voice activation or push-to-talk buttons to switch on the sound only when the user speaks.
- Frequency range. Some devices have a limited frequency range, e.g., SpeechEasy is 200-8000 Hz  and can't reproduce the typically 125 Hz adult male fundamental frequency of phonation, and so are unable to support stuttering therapy that helps stutterers to develop vocal fold awareness and control.
- Hearing impairment. Some AAF devices are molded into the user's ear, occluding (blocking) hearing.
- Telephone interface. Some DAF/FAF devices plug into telephones.
- Third-party payment. Many government agencies and insurance companies pay for AAF devices.
Telephone calls to businesses are considered "an especially problematic speaking activity" for adult stutterers.  Zimmerman  had adult stutterers call businesses in New York City using Casa Futura Technologies DAF/FAF telephone devices, asking scripted questions, without speech therapy; stuttering was reduced 55% with FAF and 60% with DAF. Brenaut  conducted a similar study in Halifax and found a 75% reduction in stuttering for a combination of DAF and FAF.
Armson  had stutterers use DAF and FAF for public speaking to an audience, finding a 74% reduction in stuttering.
Pollard  had adult stutterers wear SpeechEasy devices for four months. Their speech was tested in three conditions: reading aloud in a speech clinic (low stress), conversation with a speech-language pathologist (more stress), and asking scripted questions of strangers (highest stress, e.g., in a library asking a stranger where the bathroom is). Of the nine subjects who completed the study (one dropped out due to "intolerable background noise"), the devices were more effective for reading aloud (75% less stuttering initially, 58% less during the four month trial, with 27% carryover in the month after discontinuing using the device), less effective in conversations (27%; 15%; 7%), and least effective in asking questions of strangers (2%; 2%). 36% of the subjects bought the devices for $1800 (the regular price with fees is $4900). No relationship was found between a device's effectiveness for an individual and whether the individual bought the device. 80% complained about "irritating background noise" with the device.
Van Borsel  found that Casa Futura Technologies School DAF devices (without speech therapy) immediately reduced stuttering about 70% in a variety of speaking tasks including conversations. On average 37 minutes use of the devices per day for three months resulted in 55% carryover fluency, when the subjects spoke without the devices. No statistically significant adaptation or "wearing off" of effectiveness over time was found.
Radford  found that 14 hours use of a Casa Futura Technologies School DAF with therapy reduced stuttering more than 50% when speaking without the device, and this carryover fluency was retained for one year.
Stuart  found that SpeechEasy devices (with brief speech therapy) reduced stuttering about 90% for reading aloud and 67% for monologues. No adaptation ("wearing off") or carryover fluency was seen after four months or twelve months.
O'Donnell  found that in monologues in the speech clinic SpeechEasy devices reduced stuttering 89%, and that during telephone conversations with a speech-language pathologist over 16 weeks the devices reduced stuttering 58%. Some carryover fluency was seen (possibly because two subjects also had speech therapy).
Molt  in a study of SpeechEasy devices, found a "pattern of initial improvement followed by gradual relapse that improvements in fluency scores and on qualitative measures held for the majority of participants after 3 months but were less pronounced at 6 and 12 months postfitting."
Armson  found that speech therapy increased the effectiveness of SpeechEasy devices in a speech clinic from 42% to 74% for reading aloud, from 30% to 36% for monologues, and from 36% to 49% for conversations with a speech-language pathologist.
SpeechEasy devices are effective for reading aloud and monologues in quiet speech clinics    but ineffective in stressful conversations.  Over time, the devices don't train carryover fluency.  Some studies found that SpeechEasy devices lose effectiveness over time   while other studies found no adaptation.  SpeechEasy devices have problems with background noise.  SpeechEasy devices use a type of AAF that has never been proven to reduce stuttering; microphones that pick up background noise; and receivers that are monaural, incapable of reproducing the full frequency range of human speech, and have a maximum volume (105 db) with the potential of causing hearing loss.  The devices lack a telephone interface.
Casa Futura Technologies devices are effective in stressful speaking situations   as well as oral reading.      Over time, the devices train carryover fluency and don't lose effectiveness.   No studies reported problems with background noise. The devices use DAF and FAF, noise-cancelling microphones, wide frequency range binaural receivers, and a telephone interface. The devices have been tested and certified regarding hearing safety and other factors by Underwriters Laboratories (UL) and ESZ Elektronik-Service GmbH (CE Mark).
Biofeedback is the measurement and display of physiological processes in real time to enable users to develop awareness and control of those physiological processes. The physiological processes of speech production are respiration, phonation (vocal folds), and articulation (lips, jaw, and tongue). When a clinician trains fluent speech motor skills to a stutterer biofeedback can provide knowledge of results (KR) faster and more accurately than the clinician. E.g., if a SLP wants a stutterer to keep his or her masseter (jaw muscle) relaxed during speech, an electromyography (EMG) can instantly display when the stutterer tenses that muscle.
Imagine that we want to build a biofeedback device to treat stuttering.  We'd need a respiration monitor, an airflow monitor, a microphone to monitor vocal volume, and multichannel EMG to monitor muscle activity in the vocal folds, lips, jaw, and tongue. Because stuttering is a disorder of timing and coordination we'd need a computer program to track and coordinate the data from the sensors. While imaginable, such a biofeedback device is unfeasible due to expense, complexity, training time, and the impossibility of using such a device outside of a speech clinic. Instead, actual biofeedback devices for treating stuttering have sought to find one or two physiological processes that are central or key to stuttering.
Electromyography (EMG) uses electrodes taped to the user's skin to monitor muscle activity. Articulation muscles such as lips and jaws are easily monitored. Vocal folds are too deep in the neck to be monitored with surface electrodes.
Craig and Hancock  divided 98 school-age stutterers into four groups: one group went to a speech clinic for prolonged speech stuttering therapy (a.k.a. "smooth speech" or fluency shaping) with a SLP; in the second group, the parents went to the speech clinic and learned to do the same speech therapy with their children; the third group went to the speech clinic and did the same therapy using computer-based EMG biofeedback and relatively little interaction with SLPs; and the fourth group received no therapy. At the end of each therapy program, all three therapies reduced stuttering below 1% on average. One year after the therapy program, the children who'd done the EMG biofeedback were the most fluent (71% under 2% stuttering and 44% under 1% stuttering); the children whose parents who been involved were a close second (63% and 37%); and the children who'd had therapy with a speech-language pathologist were a distant third (48% and 10%).
While the results of this study were impressive EMG biofeedback has never caught on. The inability to monitor vocal fold activity is an important shortcoming. Another problem is false positive readings from smiling and swallowing. Another problem is the electrodes and wires all over a stutterer's throat and face. EMGs are expensive, difficult to use, and don't improve stuttering therapy enough to justify the required time and expense, i.e., training parents to do therapy at home was almost as big an improvement as EMG biofeedback.
After using EMG biofeedback I noticed that my vocal pitch dropped when the EMG device indicated that my speech production muscles were relaxed. I built a device that displayed my vocal pitch as a series of green, yellow, and red lights. I found this device to be as effective as EMG biofeedback, without the electrodes and wires and at a fraction of the cost. I especially liked that a lower vocal pitch made my voice sound confident, authoritative, and even "sexy."
When I trained other adult male stutterers to relax their breathing, relax their vocal folds, and lower their vocal pitch while using vocal pitch biofeedback all were able to speak fluently. However, I found that female SLPs had difficulty teaching this because they lacked the vocal range of adult men. No researcher has investigated whether lower vocal pitch is an effective target for treating stuttering.
Gradual changes in vocal volume keep the Hollins Communication Research Institute's (HCRI) Voice Monitor's green light on; abrupt changes in vocal volume extinguish the light. Stutterers use the device to practice gentle onsets, i.e., to gradually increase phonation volume while prolonging syllable length. No research has been published on the effectiveness of the Voice Monitor or the HCRI program.
The Computer-Aided Fluency Establishment and Trainer (CAFET) was an Apple II-based device that measured vocal volume (via a microphone) and respiration (via a chest strap). It supported eight therapy targets: relaxed, diaphragmatic breathing; continuous breathing, as opposed to breath holding; gradual exhalation, as opposed to the rapid, uncontrolled exhalation associated with stuttering; pre-voice exhalation, or letting a little air out before you begin tensing your vocal folds; gentle onset, or gradually increasing vocal volume; continuous phonation; adequate breath support, as opposed to talking after the point at which you should take another breath, and phrasing.
Tellis  investigated four adult stutterers, finding that the treatment reduced stuttering more than 80%. Six months later, three of the four subjects continued to be fluent and one relapsed, saying that he often forgot how to use the fluency techniques. Subjects were tested for reading aloud and conversation in a speech clinic.
The CAFET was introduced in the early 1980s and discontinued in the late 1990s; about one hundred speech clinics used the devices. Clinicians had to fly to Virginia for a week of training before using the CAFET.
Prolonged speech stuttering therapy trains stutterers to slow down their speech by stretching syllables as long as one or two seconds, or five to ten times slower than normal speech. Minimum Phonated Interval (MPI) stuttering therapy instead trains stutterers to eliminate only the fastest elements of speech. The result is fluent, normal-sounding speech at a normal speaking rate.
Ingham  trained five adult stutterers to use the MPI device. The subjects then came to the speech clinic to use the device on their own, with minimal SLP supervision. They practiced 2-3 hours per day for 2-3 weeks. All five subjects were then "near zero" stuttering on telephone calls to local businesses (a stressful speaking situation). A year later all five had maintained this fluency.
MPiStutter is an iOS app that supports MPI stuttering therapy.
Many adult stutterers say that the psychological effects of stuttering can be more disabling than the physical disfluencies. Cognitive-bias modification (CBM) is a new therapy for social phobia and other psychological disorders.  It uses no drugs and doesn't involve a therapist. The patient instead uses a computer program that displays two words or pictures. One is neutral and the other is threatening, e.g., a quiet garden vs. a crowded party. A stutterer may prefer the quiet garden but the computer instead requires completing tasks involving the crowded party, such as identifying letters that appear in its place on the screen. This procedure is then repeated about a thousand times, over about two hours.
CBM is based on a theory that automatic, unconscious biases in thinking are the basis of some psychological disorders. E.g., a stutterer may automatically or unconsciously respond to social situations by thinking that he or she can't interact with people. CBM changes this unconscious bias.
CBM has been proven effective for treating anxiety, depression, and addictions. It has not been tested on stutterers.
Researchers at Harvard University have developed an iPhone and Android app for treating social anxiety. You can receive the app for free if you participate in a study.
In the future perhaps stutterers will use an app on their smartphone before a stressful speaking situation. E.g., while you're waiting for a job interview you use your iPhone to treat your anxiety.
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 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, 40, 1130-1134, October 1997.
 Brenaut, L., Morrison, S., Kalinowski, J., Armson, J., & Stuart, A. (1995). Effect of altered auditory feedback on stuttering during telephone use. Poster session presented at the national convention of the American Speech-Language Hearing Association, Orlando, FL.
 Pollard, R., Ellis, J., Finan, D., & Ramig, P. (2009). Effects of the SpeechEasy on objective and perceived aspects of stuttering: a 6-month, phase I clinical trial in naturalistic environments. Journal of Speech, Language, and Hearing Research, 52, 516-533.
 Van Borsel, J., Reunes, G., & Van den Bergh, N. (2003). Delayed auditory feedback in the treatment of stuttering: clients as consumers. Intl J Language Comm Dis, 38:2, 119-129.
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 Molt, L. (2006). SpeechEasy AAF device long-term clinical trial: Usage patterns and satisfaction ratings. Poster presented at the annual convention of the American Speech-Language-Hearing Association, Miami, FL. Quote is from Pollard, R., Ellis, J., Finan, D., & Ramig, P. (2009). Effects of the SpeechEasy on objective and perceived aspects of stuttering: a 6-month, phase I clinical trial in naturalistic environments. Journal of Speech, Language, and Hearing Research, 52, 516-533.
 Armson, J., Kiefte, M., Mason, J., & De Croos, D. (2006). "The effect of SpeechEasy on stuttering frequency in laboratory conditions." Journal of Fluency Disorders, 31, 137-152.
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 Askenfelt, A., Gauffin, J., Sundberg, J., & Kitzing, P. (1980). A comparison of contact microphone and electroglottograph for the measurement of vocal fundamental frequency. Journal of Speech and Hearing Research, 1980 June; 23(2): 258-73.
 Natke, U. (2000) Stotterreduktion unter verzögerter und frequenzverschobener auditiver Rückmeldung/Reduction of stuttering frequency using frequency-shifted and delayed auditory feedback. Folia Phoniatrica et Logopaedica, 52 (4), 151-159.
 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.
 Antipova, E., Purdy, S., Blakeley, M., & Williams, S. (2008) "Effects of altered auditory feedback (AAF) on stuttering frequency during monologue speech production," Journal of Fluency Disorders, 33:4, December 2008, 274-290.
 Michelle Lincoln, Ann Packman, Mark Onslow, Mark Jones. (2010). An experimental investigation of the effect of AAF on the conversational speech of adults who stutter. Journal of Speech, Language, and Hearing Research, October 2010, 53, 1122-1131.
 Unger, J., Glück, C., & Cholewa, J. Immediate effects of AAF devices on the characteristics of stuttering: A clinical analysis. Journal of Fluency Disorders 37 (2012) 122134.