Altered auditory feedback (AAF) such as singing, choral speaking, masking, delayed or frequency altered feedback have long been known to reduce stuttering. Early altered auditory feedback devices were large and thus confined to the laboratory or therapy room, but advances in electronics have permitted increasingly portable devices such as the Speak For Less FluencyPods, the Voiceamp, the Casa Futura Tech DAF devices, the Derazne Correctophone, the Edinburgh Masker, the Vocaltech Clinical Vocal Feedback Device, the Fluency Master and the SpeechEasy. Current devices may be similar in size and appearance to a
hearing aid, including in-the-ear and completely-in-the-canal models. Clinic-based and portable devices, such as the Edinburgh Masker (since discontinued) have been developed to deliver masking, and found that masking was effective in reducing stuttering, though many found that reduction in stuttering faded with time. 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. A DAF user hears their voice in headphones, delayed a fraction of a second. Typical delays are in the 50 millisecond to 200 millisecond range. 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 their 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. 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. In addition, studies have been critiqued for failing to demonstrate
ecological validity; in particular that AAF effects continue over the long term and in everyday speaking situations. There are few published studies on the effect of the AAF in the daily activities of life; studies have mainly examined the effect of AAF on short oral reading tasks, with some studying the giving of a monologue that is usually short in duration. Several studies have produced group results that stutterers using the SpeechEasy show greater reductions in reading than for monologue and conversation. and some anecdotal reports suggest that over time users receive continued but lessened effects from their device. While one group study has reported continued overall reductions in stuttering after a year of daily use of the SpeechEasy on reading and a monologue task, while others have not. The effective of electronic fluency devices as measured by qualitative measures and ratings by stutterers have also been made. Studies show that some stutterers report improved fluency and confidence about speaking, and less severe stuttering and some carryover effects; the device is perceived as being particularly useful on the telephone. They reported that the device was difficult to use in noisy situations as the device amplifies all voices and sounds, 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. 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 as a possible cause of stuttering reduction with AAF. ==References==