Electronic fluency devices

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



Types
Electronic fluency devices can be divided into two basic categories.
 * Computerized feedback devices provide feedback on the physiological control of respiration and phonation, including loudness, vocal intensity and breathing patterns.


 * Altered auditory feedback (AAF) devices alter the speech signal so that speakers hear their voices differently.

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

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

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

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

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

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

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

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

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

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