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Technology for Stuttering Treatment

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Each technology will be judged as useful or not by the preceding three criteria:

  1. 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, etc. Another improvement is to enable speech-language pathologists (SLPs) without specialized training in fluency disorders to treat stuttering effectively.
  2. 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.
  3. 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.

ALTERED AUDITORY FEEDBACK

Altering how people hear their voices, called altered auditory feedback (AAF), changes how they speak and can improve the fluency of stutterers. A well-known example is the chorus effect, in which a stutterer speaks or reads in chorus with another person.

Lincoln [2] 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 trained carryover fluency (when users weren't wearing the device).

Delayed Auditory Feedback (DAF)

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 [3] .

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 reduced stuttering to under 2% and resulted in long-term carryover fluency, for both adults and children [4] .

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" [5] . Then in a seminal 1993 paper Kalinowski [1] 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" [6]

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 [7] .

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. I have other symptoms associated with CAPD. I prefer to watch movies with the subtitles on. I can't "pick up" foreign languages by ear. If there's background noise, such as at a loud party or outside on a windy day, I can't understand what people are saying.

The auditory processing underactivity associated with stuttering is specifically in areas "thought to support self-monitoring of speech production" [8] . Braun [9] 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; and a short delay stimulates the brain's auditory processing area and reduces stuttering (typically 70% [10] ) at normal speaking rates with normal-sounding speech, without training or speech therapy or cognitive effort. Traditional stuttering therapy doesn't treat the abnormal auditory processing associated with stuttering, so DAF meets criterion #2.

In my experience, 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. Downloadable DAF software applications include:

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 stutterers have the opposite: their right PT is larger than their left PT (rightward asymmetry), and that stutterers with this abnormal rightward asymmetry stuttered more severely and had significantly improved fluency with DAF compared to stutterers with the normal leftward asymmetry [11] .

Frequency-Altered Auditory Feedback (FAF)

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 [12]

FAF also induces speech motor changes, specifically vocal pitch changes. [13] 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 but in my experience lower is 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 Altered Auditory Feedback

Other types of AAF include:

Synthesized sine waves synchronized to phonation, e.g., the Edinburgh Masker. Block [15] found that the device reduced stuttering about 50%. Dewar [16] 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 [17] 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 [1] 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 [14] found a metronome to be less effective than DAF.

Technical Aspects of Altered Auditory Feedback

Not all AAF devices are alike:

  • Monaural vs. binaural. Stuart [18] 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 [19] 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. See the article Funding for Stuttering Treatment.

Effectiveness of Portable AAF Devices in Stressful Speaking Situations

Telephone calls to businesses are considered "an especially problematic speaking activity" for adult stutterers [20] . Zimmerman [21] 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 [22] conducted a similar study in Halifax and found a 79% reduction in stuttering for a combination of DAF and FAF.

Armson [30] had stutterers use fixed laboratory equipment providing DAF and FAF for public speaking to an audience, finding a 74% reduction in stuttering.

Pollard [23] 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% (including the subject who dropped out) complained about "irritating background noise" with the device.

Long-Term Effects of Portable AAF Devices

Van Borsel [24] found that Casa Futura Technologies 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 [25] found that 14 hours use of a Casa Futura Technologies DAF device with therapy reduced stuttering more than 50% when speaking without the device, and this carryover fluency was retained for one year.

Stuart [26] 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 [27] 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 [28] 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."

Effects of Speech Therapy with Portable AAF Devices

Armson [29] 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.

Summary of SpeechEasy Studies

SpeechEasy devices are effective for reading aloud and monologues in quiet speech clinics [23] [26] [27] but ineffective in stressful conversations. [23] Over time, the devices don't train carryover fluency. [26] Some studies found that SpeechEasy devices lose effectiveness over time [28] [23] while other studies found no adaptation. [26] SpeechEasy devices have problems with background noise. [23] 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. [19] The devices lack a telephone interface.

Summary of Casa Futura Technologies Studies

Casa Futura Technologies devices are effective in stressful speaking situations [22] [21] as well as oral reading. [24] [36] [37] [38] [39] Over time, the devices train carryover fluency and don't lose effectiveness. [24] [25] 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

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. [31] 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 complex 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

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 [32] 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.

Vocal Pitch

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 me feel confident and authoritative.

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 almost 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.

Gentle Onsets

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 Voice Monitor isn't widely used outside of the HCRI clinic. We don't know if the device meets the first criteria (enhancing therapy effectiveness). It doesn't meet the second criteria, i.e., stutterers can practice gentle onsets without the device. A iPhone version enables stutterers to practice gentle onsets at home, partially meeting the third criteria, but it's not clear whether the app could be use in stressful speaking situation (does it produce normal-sounding speech?) or in noisy environments.

CAFET

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 [33] 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. I contacted Martha Goebel, the developer of the CAFET, to discuss building a CAFET app for the iPhone. We agreed that this wouldn't be feasible because the CAFET required SLP supervision to use it, i.e., it wouldn't work well outside of a speech clinic.

Minimum Phonated Interval (MPI) Stuttering Therapy

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.

MPI stuttering therapy uses an accelerometer worn on an elastic neckband. The accelerometer is as accurate as an electroglottograph (EGG) for monitoring vocal fold activity [34] . It doesn't pick up background noise and doesn't have "false positives" from smiling or swallowing.

The accelerometer is connected to a computer that measures the length of phonated intervals, i.e., the periods that the user's vocal folds are vibrating to produce vowels and voiced consonants, delineated by voiceless consonants and pauses. The computer then displays the user's vocal volume as a moving line graph (i.e., loudness curves) and color-codes each phonated interval as to length, e.g., red for too short (under 100 milliseconds), green for ideal, and blue for abnormally long or slow speech. The main window displays the last two seconds of the user's speech. Above the main window a bar graph displays the last twenty minutes of the user's speech (i.e., short red bars indicate few short phonated intervals; a tall blue bar indicates many long phonated intervals). The user tries to produce green intervals and not to produce red intervals.

Ingham [20] 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 "stutter free" in telephone calls to local businesses (a stressful speaking situation). A year later all five had maintained this fluency.

What caught my eye about MPI stuttering therapy was that the subjects were able to use the device on their own. My company, Casa Futura Technologies, has developed the iStutter iPhone (and iPod touch) app for MPI stuttering therapy. The device meets all three of the criteria: a published study finding that MPI stuttering therapy was at least as effective as traditional stuttering therapies; the device monitors an aspect of stuttering that no other therapy addresses, i.e., too-short speech elements; and the device can be used outside of speech clinics in stressful speaking situations.

The iStutter iPhone app adds several features not in the original MPI stuttering therapy software. Red phonated intervals switch in delayed auditory feedback (DAF) to induce the user to slow down and improve fluency. When the user is back in control of his speech green (or blue) intervals switch off the DAF.

The iStutter app also logs the user's speech data during the day. When the user plugs his iPhone into his computer to recharge overnight, the app automatically e-mails the data to the user's SLP. The SLP can then check on each of her clients every morning.

Another screen displays "Arthur the Young Rat." When the user reads the story his syllables per second and percentage of too-short, ideal, and too-long phonated intervals is displayed. The results can be e-mailed to an SLP.

TECHNOLOGY FOR TREATING PSYCHOLOGICAL EFFECTS OF STUTTERING

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 [35] . 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.

References

[1] Kalinowski, J., Armson, J., Stuart, A., Graco, V., & Roland-Mieskowski, M. (1993). Effects of alterations in auditory feedback and speech rate on stuttering frequency. Language and Speech, 36, 1-16. See also Bloodstein, O., & Bernstein, N. (2008). A Handbook on Stuttering, Sixth Edition. Clifton Park, NY: Thomson Delmar Learning, pages 295-298.

[2] Lincoln, M., Packman, A., & Onslow, M. (2006) Altered auditory feedback and the treatment of stuttering: A review. Journal of Fluency Disorders, 31, 71-89.

[3] Bothe, A., Davidow, J., Bramlett, R., & Ingham, R. 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, November 2006.

[4] Ryan, B., & Van Kirk, B. (1974). The establishment, transfer and maintenance of fluent speech in 50 stutterers using delayed auditory feedback and operant procedures. Journal of Speech and Hearing Disorders, 39:1. Ryan, B. & Van Kirk, B. (1995). Programmed stuttering treatment for children: Comparison of two establishment programs through transfer, maintenance, and follow-up. Journal of Speech and Hearing Research, 38:1.

[5] Costello-Ingham, J. (1993) Current status of stuttering and behavior modification—I: Recent trends in the application of behavior modification in children and adults. Journal of Fluency Disorders, 18:1, p. 30.

[6] 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, (3), 259-269.

[7] Kutscher, Martin L. (2005). Kids in the Syndrome Mix. (Jessica Kingsley Publishers, ISBN 1-84310-8100), pages 178-179.

[8] Bloodstein, O., & Bernstein, N. (2008a). A Handbook on Stuttering, Sixth Edition. Clifton Park, NY: Thomson Delmar Learning, pages 138-140, specifically Fox (1996), Braun (1997), Fox (2000), and De Nil (2004). See also Rastatter, M.P., Stuart, A., & Kalinowski, J. (1998). Quantitative Electroencephalogram of Posterior Cortical Areas of Fluent and Stuttering Participants During Reading with Normal and Altered Auditory Feedback. Perceptual and Motor Skills, 87, (2), 623-633.

[9] Braun, A., Varga, M., Stager, S., Schulz, G., Selbie, S., Maisog, J., Carsom, R., & Ludlow, C. (1997). "Atypical Lateralization of Hemispheral Activity in Developmental Stuttering: An H215O Positron Emission Tomography Study," 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.

[10] 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, (3), 259-269. 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., 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. Stager, S., Denman, D., & Ludlow, C. (1997). Modifications in aerodynamic variables by persons who stutter under fluency-evoking conditions. JSLHR, 40, 832-847. 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.

[11] Foundas, A.L., Bollich, A.B., Corey, D.M., Hurley, M., & Heilman, K.M. (2001). Anomalous Anatomy in Adults with Persistant Developmental Stuttering: A Volumetric MRI Study of Cortical Speech-Language Areas. Neurology, 57, 207-215. Foundas, A., A. M. Bollich, J. Feldman, D. M. Corey, M. Hurley, L. C. Lemen, & K. M. Heilman (2004). Aberrant auditory processing and atypical planum temporale in developmental stuttering, Neurology, 63, 1640-1646.

[12] 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, (3), 259-269. Hargrave, S., Kalinowski, J., Stuart, A., Armson, J., & Jones, K. (1994). Stuttering reduction under frequency-altered feedback at two speech rates. Journal of Speech and Hearing Research, 37, 1313-1320. [6] 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, (3), 259-269. Stuart, A., Kalinowski, J., Armson, J., Stenstrom, R., & Jones, K. (1996). Stuttering reduction under frequency-altered feedback of plus and minus one-half and one-quarter octaves at two speech rates. Journal of Speech and Hearing Research, 39, 396-401.Armson, J., Kalinowski, J., Foote, S., Witt, C., & Stuart, A. (1997). Effect of frequency altered feedback and audience size on stuttering. European Journal of Disorders of Communication, 32(3), 359-366. Ingham, R., Moglia, R., Frank, P., Ingham, J., & Cordes, A. (1997). Experimental Investigation of the Effects of Frequency-Altered Auditory Feedback on the Speech of Adults who Stutter. Journal of Speech and Hearing Research, 40:2, 361-373, April 1997. Armson, J., & Stuart, A. Effect of Extended Exposure to Frequency-Altered Feedback on Stuttering During Reading and Monologue. Journal of Speech, Language, and Hearing Research, 41, 479-490, June 1998. Howell, P., Sackin, S., & Williams, R. Differential Effects of Frequency-Shifted Feedback Between Child and Adult Stutterers. Journal of Fluency Disorders, 24 (1999) 127-136.

[13] Natke, U., Grosser, J., & Kalveram, K. (2001). Fluency, fundamental frequency, and speech rate under frequency shifted auditory feedback in stuttering and nonstuttering persons. Journal of Fluency Disorders, 26, 227-241.

[14] Stager, S., Denman, D., & Ludlow, C. (1997). Modifications in aerodynamic variables by persons who stutter under fluency-evoking conditions. JSLHR, 40, 832-847. See also Bloodstein, O., & Bernstein, N. (2008). A Handbook on Stuttering, Sixth Edition. Clifton Park, NY: Thomson Delmar Learning, pages 302-304.

[15] Block, S., Ingham, R.J., & Bench, R.J. (1996). The effects of the Edinburgh Masker on stuttering. Australian Journal of Human Communication Disorders, 24, 11-18.

[16] 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, 14(3), 19-26.

[17] Webster, R. (1991). Manipulation of vocal tone: implications for stuttering. In Peters, H., Hulstijn, W., & Starkweather, W. (Ed.), Speech Motor Controls and Stuttering. New York, NY: Elsevier.

[18] 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, 2237-2241.

[19] Stuart, A., Xia, S., Jiang, Y., Jiang, T., Kalinowski, J., & Rastatter, M. (2003) Self-contained in-the-ear device to deliver altered auditory feedback: applications for stuttering. Annals of Biomedical Engineering, 31, 233-237.

[20] Ingham, R., Kilgo, M., Ingham, J., Moglia, R., Belknap, H., & Sanchez, T. (2001). Evaluation of a stuttering treatment based on reduction of short phonation intervals. Journal of Speech, Language, and Hearing Research, 44, 1229-1244.

[21] 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.

[22] 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.

[23] 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.

[24] 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.

[25] Radford, N., Tanguma, J., Gonzalez, M., Nericcio, M.A., & Newman, D. (2005) A case study of mediated learning, delayed auditory feedback, and motor repatterning to reduce stuttering. Perceptual and Motor Skills, 101, 63-71.

[26] 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 and Communication Disorders, 39:1, 93–113. Stuart, A., Kalinowski, J., Saltuklaroglu, T., & Guntupalli, V. (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, 1-9.

[27] O'Donnell, J., Armson, J., & Kiefte, M. (2008). The effectiveness of SpeechEasy during situations of daily living. Journal of Fluency Disorders, 33, 99-119.

[28] 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.

[29] 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.

[30] Armson, J., Kalinowski, J., Foote, S., Witt, C., & Stuart, A. (1997). Effect of frequency altered feedback and audience size on stuttering. European Journal of Disorders of Communication, 32(3), 359-366.

[31] Van Riper, C. (1974). Stuttering: where and whither? Asha, September 1974. Several of Van Riper's classic articles, including this article, are downloadable from the American Speech-Language Hearing Association website at http://www.asha.org/publications/archive/magazine.htm.

[32] Craig, A., Hancock, K., Chang, E., McCready, C., Shepley, A., McCaul, A. & Reilly, K. (1996). A controlled clinical trial for stuttering in persons aged 9 to 14 years. Journal of Speech and Hearing Research, 39:4, 808-826. Hancock, K., Craig, A., McCready, C., McCaul, C., Costello, D., Campbell, K., & Gilmore, G., (1998). Two- to six-year controlled-trial stuttering outcomes for children and adolescents. Journal of Speech and Hearing Research, 41, 1242-1252.

[33] Tellis, G. (1996). Efficacy of the computer-aided fluency establishment trainer in the treatment of stuttering (Doctoral dissertation, California State University, Fresno, 1996). Dissertation Abstracts International, 57.

[34] 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.

[35] Economist (2011, March 3). Therapist-free therapy: Cognitive-bias modification may put the psychiatrist's couch out of business. http://www.economist.com/node/18276234

[36] 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.

[37] 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.

[38] 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.

[39] 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.

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