Electronic fluency device

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 Anti-stuttering devices are electronic devices intended to improve the fluency of persons who stutter. Most anti-stuttering devices change the sound of the user's voice in his or her ear. A wide variety of methods are used to alter the sound of the user's voice, with the result that different anti-stuttering devices can sound quite different. Some devices are computer-based, while others are pocket-sized, while still others are the size of hearing aids. Some devices are intended to be used with speech therapy, while others can be used without training or therapy. Some devices are intended to be used temporarily, with the user needing the device less and less over time as his or her speech improves; other devices are intended to be worn more or less permanently. Some devices are designed for specific speaking situations, such as telephone calls, while others are designed to be used in a variety of speaking situations. Some devices are intended to be as inconspicuous as possible, to help a stutterer hide his or her stuttering; other devices are not intended to be inconspicuous, reflecting a belief that one should be be open about one's stuttering to listeners.

Anti-stuttering device

Terms used

This article uses the following terms:

  • Altered auditory feedback (AAF) is anything that changes how one hears one's voice in one's ear.
  • Immediate fluency is the reduction in stuttering (if any) while the stutterer is using the anti-stuttering device.
  • Carryover fluency is the reduction in stuttering (if any) after the stutterer removes the device.
  • Wearing off of effectiveness or adaptation effect occurs when a stuttering treatment is effective when first used, but the effectiveness diminishes over time (days, weeks, or months).
  • Transfer refers to learning to speak fluently in a speech clinic, and then transferring this fluent speech to higher stress conversations outside the speech clinic.

Types of altered-auditory feedback (AAF)

  • The oldest and simplest altered auditory feedback is choral speaking, that is, a stutterer speaks in chorus with another person, for example, reciting the Pledge of Allegiance as part of a group.
  • Metronomes were used historically by speech-language pathologists to train stutterers to speak with altered rhythm, with one syllable per beat of the metronome. The result was typically less stuttering but sounded abnormal. Additionally the dual-tasking mental effort made conversations difficult. In one study, using a metronome 100% eliminated stuttering, with the metronome set at 92 syllables per minute, or about three times slower than normal speech.[1]
  • Sine wave masking analyzes the user's voice to determine the fundamental frequency or vibrating frequency of the user's vocal folds, then synthesizes a sine wave at this frequency (vocal fold vibration is a sine wave). Typically this is accomplished with a phase locked loop. Sine wave masking is the only type of AAF that can pull stutterers out of silent blocks (in which the stutterer locks his or her vocal folds and can't produce any sound); sine wave masking devices generally have a button to push to start the sound and relieve silent blocks. White noise masking and sine wave masking are often confused, and both are called masking auditory feedback (MAF). The Edinburgh Masker anti-stuttering device provided sine wave masking.
  • Delayed auditory feedback (DAF) was first used to reduce stuttering in 1964. A DAF user hears his or her voice in headphones, delayed a fraction of a second. Typical delays are in the 50 millisecond to 200 millisecond range (one-twentieth to one-fifth of a second). Short delays (in the 50 millisecond to 75 millisecond range) and long delays (in the 100 millisecond to 200 millisecond range) has different effects. A short delay reduces stuttering typically 70%, at normal speaking rates, without training, speech therapy, or abnormal-sounding speech.[2][3][unreliable source?][4][5] A longer delay can induce in a slower speaking rate and even less stuttering. For example, a 195 millisecond delay reduced stuttering 85% while also slowing speaking rate 60%.[1] Some stuttering therapy programs use this slow speech to train other fluent speech motor skills, such as speaking with relaxed breathing, relaxed vocal folds, or relaxed lips, jaw, and tongue. When the stutterer masters these 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.
  • Pitch-shifting or frequency-altered auditory feedback (FAF) changes the pitch at which the user hears his or her voice. For example, an adult male whose vocal folds vibrate around 125 Hz may hear his voice shifted up one octave 10 250 Hz, or shifted down one octave to 62 Hz. Most studies have found that a quarter-octave pitch shift (up or down) has some effect, and that a maximum effectiveness of typically 70% is reached at one half or one octave (up or down). Combining DAF with pitch-shifting FAF increases effectiveness to typically 80%.[2][4][unreliable source?][5][6][7][8] Pitch-shifting FAF reduces stuttering at normal speaking rates, without training, speech therapy, or abnormal-sounding speech. The referenced studies found that upward and downward pitch shifts were equally effective for short-term fluency, however, no long-term studies have compared upshifts to downshifts. Studies with non-stutterers have found that FAF induces changes in vocal fold tension.[9][10][11]Speculatively, FAF upshift devices might improve stutterers' auditory processing and result in immediate fluency, but train stutterers to speak with increased vocal fold tension and result in "wearing off" of effectiveness or even make speech worse over time. FAF downshift devices might train stutterers to speak with relaxed vocal folds and improve carryover fluency. More research is needed in this area.
  • Frequency-shifting frequency-altered auditory feedback (FAF) adds or subtracts a fixed frequency, typically 500 Hz, 1000Hz, or 2000 Hz, to or from the user's voice. Frequency shifting to add 500 Hz sounds not unlike pitch-shifting up about one octave. However subtracting a fixed frequency sounds completely different from downward pitch-shifting. Subtracting a fixed frequency doesn't lower the pitch but rather acts as a high-pass filter. For example, adult male vocal folds typically vibrate around 125 Hz. Pitch-shifting down one octave reduces in a 62 Hz signal. Subtracting 500 Hz results in no sound, as 125 minus 500 is nothing (there are no negative frequencies). Typically a hearing aid can't produce sound below 200 Hz so subtracting 500 Hz cuts off all sound input below 700 Hz, which is most of the human vocal signal. For these reasons frequency-shifting FAF is almost used in the addition mode (typically 500 Hz up), and rarely used in the subtraction mode. No studies have been published investigating the effective (if any) of frequency-shifting FAF alone on stuttering.
  • Some anti-stuttering devices use a special microphone to pick up the user's vocal fold vibrations (phonation). The microphone is usually in physical contact with the user's throat or another area (such as the bone behind the ear) where vocal fold vibrations can be picked up. Such a device can be helpful if a speech-language pathologist is training a stutterer to develop better vocal fold awareness and control. Some anti-stuttering devices use such a throat microphone with DAF or FAF, while other devices simply amplify the user's phonation without a delay or other effect. Little research has been done on the effectiveness of the latter.

Unknown effects of altered auditory feedback (AAF)

  • The effects of AAF in stutterers' brains is unknown. The devices likely reduce some neurological abnormality associated with stuttering. However, no brain scans have been done of stutterers using AAF. Brain scan studies of stutterers have found, in general, two abnormalities during stuttering:[12][13][14][15][page needed][16][page needed] stutterers appear to have underactivity in the central auditory processing area, and stutterers appear to have overactivity in the speech motor control area (the latter observation may explain why stuttering is characterized by overtense speech production muscles, and stuttering therapy programs often train stutterers to speak with relaxed speech-production muscles). Speculatively, AAF devices affect the brains of stutterers in one or both of two ways: increasing activity in the auditory processing area, and/or reducing speech motor activity. Such a dual model hypothesis may explain why there seems to be a wide range of effects from anti-stuttering devices: some devices may affect the auditory processing area but not the speech motor area, or vice versa, or both, etc. More research is needed in this area.
  • The long-term effects of AAF devices have been the subject of several studies. Some studies have found carryover fluency, i.e., increased effectiveness over time[17][18]; one study found "wearing off" or diminished effectiveness over time[unreliable source?][19]; and still other studies have found no changes in effectiveness over time.[20][21] Further research is needed to determine why differing results have been found.
  • The relationship between AAF anti-stuttering devices and speech therapy hasn't been studied carefully. Some studies have found that the combination of therapy and a device is more effective than the device alone,[failed verification] [22][23] however, these studies didn't have a control group that only received the therapy, making it difficult to compare the effectiveness of a device, a therapy program, and the combination of a device plus a therapy program.
  • If AAF anti-stuttering devices alter brain activity then the long-term effects of AAF devices on children, whose brains are still growing, could be different from the effects on adult stutterers. Because stuttering is a developmental disorder, extensive use of an AAF device might cause a child's brain to develop normally instead of on the abnormal stuttering development path, or extensive use of an AAF device might cause a child's brain to develop on another, unknown abnormal developmental path. More research is needed in this area.
  • The effects of AAF anti-stuttering devices on hearing is unknown. Hearing safety is likely not an issue with AAF devices that are used in quiet environments, such as speech clinics or anti-stuttering telephone devices used in a quiet office. Noise-induced hearing loss may be an issue with AAF devices used in noisy environments such as classrooms or restaurants.

Other differences between anti-stuttering devices

  • Size. Anti-stuttering devices range from computer-based, typically used with a full-size headset; to the size of an iPod, typically used with miniature earsets made for cellphones; to the size of a hearing aid.
  • Background noise rejection. Some anti-stuttering devices have no anti-background noise features and are best used in a quiet environment. such as a speech clinic or making telephone calls from one's home. Other anti-stuttering devices have features to reject background noise in environments such as classrooms or restaurants.
  • Monaural or binaural. Binaural (two ears) anti-stuttering devices are about 25% more effective than monaural (one ear) anti-stuttering devices.[24]
  • Frequency range. Many stuttering therapy programs focus on improving vocal fold awareness and control ("gentle onsets," "easy onsets," etc.). Adult male vocal folds vibrate around 125 Hz; women's and children's vocal folds vibrate around 200 to 250 Hz. Some anti-stuttering devices can reproduce the full range of human vocal frequencies, but other anti-stuttering devices, such as some hearing aid-size devices, can only reproduce a narrow range of frequencies.[25] No research has investigated whether limiting frequency range reduces the effectiveness of an anti-stuttering device.

Studies of anti-stuttering devices

  • A survey of 67 stutterers who used the Edinburgh Masker, a pocket-sized sine wave masking device with binaural (two ears) earphones, for six months found that 82% said the device continued to be highly effective. 67% said that, "as the result of using the device, their unaided speech fluency had improved" (carryover fluency). The average volume was 78 dB.[failed verification][26]
  • A study of 21 adult stutterers using the Fluency Master, a monaural (one ear) hearing-aid size device that amplifies the user's vocal fold vibrations via a microphone contacting the user's skin, found that stuttering in conversations was reduced on average 14%.[failed verification] [22]
  • Two studies investigated Casa Futura Technologies anti-stuttering telephone devices with DAF and pitch-shifting FAF and binaural (two ears) headphones. Both studies had the subjects make scripted telephone calls to local businesses (a high-stress speaking situation for most stutterers). The first study had seven adult subjects and found an 80% reduction in stuttering.[4][unreliable source?] The second study had nine adult subjects and found a 60% reduction in stuttering.[5]
  • A study compared DAF and pitch-shifting FAF in eight adult stutterers, using a a desktop-size Casa Futura Technologies anti-stuttering device with binaural (two ears) headphones. The study found that DAF reduced stuttering in all eight subjects and pitch-shifting FAF reduced stuttering in four of the eight subjects.[27]
  • A study found significant differences between eleven adult men and eleven adult women using a desktop-size Casa Futura Technologies anti-stuttering device with DAF and pitch-shifting FAF with binaural (two ears) headphones. In the women subjects, DAF reduced stuttering 71% and pitch-shifting FAF reduced stuttering 64%. In the men subjects, DAF reduced stuttering 33% and pitch-shifting FAF reduced stuttering 31%.[unreliable source?][28]
  • A study compared the effectiveness of two anti-stuttering devices with a single subject. One device was a Casa Futura Technologies pocket-size device with DAF and pitch-shifting FAF and a wireless monaural (one ear) earset. The other device was a monaural (one ear) SpeechEasy hearing aid-size device with DAF and frequency-shifting FAF. The study found that the pocket-size device was more than twice as effective as the hearing aid-size device.[unreliable source?][29]
Long-term effects with School DAF
  • A study investigated nine adult stutterers using Casa Futura Technologies School DAF devices, a pocket-size DAF device with binaural (two ears) headphones. The subjects didn't receive speech therapy. They used the devices an average of thirty minutes per day. The devices initially reduced stuttering about 70%, and no statistically significant change in effectiveness was seen after three months. After three months the subjects had 55% carryover fluency (when speaking without the devices).[17]
  • A study investigated one 11-year-old boy who used a Casa Futura Technologies School DAF device, a pocket-size DAF device with binaural (two ears) headphones. The subject used the device for fourteen hours in conjunction with speech therapy. The boy's stuttering was reduced 50% (to less than 5% dysfluencies). One year later his stuttering was at the same level (less than 5% dysfluencies), i.e., carryover fluency. Another fourteen hours of the same treatment reduced his stuttering an additional 17% (to 4% dysfluencies).[18]
Long-term effects with SpeechEasy
  • A study investigated nine stutterers (five adults and four children) using SpeechEasy hearing aid-style monaural (one ear) anti-stuttering device with DAF and frequency-shifting FAF. The subjects used the devices about seven hours per day. Their fluency was measured after four months and after twelve months. The subjects were tested reading aloud and in a monologue task in a speech clinic. The delay was set at 60 milliseconds and the FAF at 500 Hz up. The subjects received brief speech therapy. The devices reduced stuttering about 80%. No statistically significant carryover fluency or "wearing off" of effectiveness was found.[20][21]
  • A study investigated thirteen adult stutterers using SpeechEasy hearing aid-style monaural (one ear) anti-stuttering device with DAF and frequency-shifting FAF. The subjects were tested in three speaking tasks: reading, monologue, and conversation, all in a speech clinic. On average stuttering was reduced 36%. The subjects were then given speech therapy and the combination of therapy and the device reduced stuttering 53%.[23]
  • A study investigated adult stutterers using SpeechEasy hearing aid-style monaural (one ear) anti-stuttering device with DAF and frequency-shifting FAF. The subjects were followed up for up to three years. Of nineteen original subjects, twelve (63%) had excellent initial results, with 1% or less stuttering. Two subjects (11%) experienced no improvement in their speech. On average, the devices reduced stuttering initially about 75%. Eleven of the nineteen subjects purchased the devices. Two of the eleven subjects returned the devices for refunds). The nine subjects who kept the devices were re-evaluated an average of seven months later. Four continued to have excellent speech (1% or less stuttering). One person who had only good results initially now had excellent results (an improvement over six months). One person who had excellent results initially now had only good results. Two others had speech worse than before using the device. On average, after seven months the devices reduced stuttering about 57%. Six subjects returned for a second follow-up, on average eighteen months after purchasing the devices. Two subjects were stuttering about as much as before they purchased the device. The other four subjects were worse. On average, after eighteen months the devices now increased stuttering about 50%. Five subjects were tested at a third follow-up, on average after 30 months using the device. One subject had better speech after 30 months than before using the device (his stuttering dropped from 30% to 17%). Two subjects appear to have speech about the same as before using the device. One subject had moderately worse speech, and one had substantially worse speech (stuttering went from 2% to 9%). Adding the three additional subjects who were tested at the second follow-up but not the third follow-up, this study raises questions of whether five of eight SpeechEasy users had worse stuttering after long-term use of the device, two had speech about the same as before using the device, and one had improved speech.[unreliable source?][19]
  • A study investigated eleven adult stutterers using SpeechEasy hearing aid-style monaural (one ear) anti-stuttering device with DAF and frequency-shifting FAF. Three conditions were investigated: reading aloud, conversation with an experimenter, and asking a question to a stranger. (In other words, a low-stress speaking task, a medium-stress speaking task, and high-stress speaking task.) Speech samples were collected before using the SpeechEasy device, during a four-month period when the devices were used daily, and after the four-month trial (not using the device). The only statistically significant effect was seen in the reading task, in which stuttering was reduced about 50%. In the conversation task and in the question task no statistically significant effects were found. These results suggest that the device may be more effective in low-stress speaking tasks than in high-stress speaking tasks.[unreliable source?][30]

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