Delayed Auditory Feedback (DAF), also called delayed
sidetone
Sidetone is audible feedback to someone speaking or otherwise producing sound as an indication of active transmission. Sidetone is introduced by some communications circuits and anti-sidetone circuitry is used to control its level.
Sidetone is exp ...
, is a type of altered auditory feedback that consists of extending the time between speech and auditory perception.
It can consist of a device that enables a user to speak into a
microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
and then hear their voice in
headphones
Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an au ...
a fraction of a second later. Some DAF devices are hardware; DAF
computer software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
is also available. Most delays that produce a noticeable effect are between 50-200 milliseconds (ms). DAF usage (with a 175 ms delay) has been shown to induce
mental stress
In psychology, stress is a feeling of emotional strain and pressure. Stress is a type of psychological pain. Small amounts of stress may be beneficial, as it can improve athletic performance, motivation and reaction to the environment. Excess ...
.
[
]
It is a type of altered auditory feedback that—along with frequency-altered feedback and white noise masking—is used to treat
stuttering
Stuttering, also known as stammering, is a speech disorder in which the flow of speech is disrupted by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses or blocks in which the ...
; it has also demonstrated interesting discoveries about the auditory feedback system when used with non-stuttering individuals. It is most effective when used in both ears.
Delayed auditory feedback devices are used in
speech perception
Speech perception is the process by which the sounds of language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by wh ...
experiments in order to demonstrate the importance of
auditory feedback
Auditory feedback (AF) is an aid used by humans to control speech production and singing by helping the individual verify whether the current production of speech or singing is in accordance with his acoustic-auditory intention. This process is po ...
in
speech perception
Speech perception is the process by which the sounds of language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by wh ...
as well as in
speech production
Speech production is the process by which thoughts are translated into speech. This includes the selection of words, the organization of relevant grammatical forms, and then the articulation of the resulting sounds by the motor system using the vo ...
.
[
]
There are now also different mobile apps available that use DAF in phone calls.
Effects in people who stutter
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 devi ...
use delayed auditory feedback and have been used as a technique to aid with
stuttering
Stuttering, also known as stammering, is a speech disorder in which the flow of speech is disrupted by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses or blocks in which the ...
. Early investigators suggested and have continually been proven correct in assuming that those who stutter had an abnormal speech–auditory feedback loop that was corrected or bypassed while speaking under DAF. In people who stutter with atypical auditory anatomy, DAF improves fluency, but not in those with typical anatomy. DAF is also used with people who
clutter
Clutter and its derivations may refer to any of the following:
Excessive physical disorder
* Clutter, a confusing, or disorderly, state or collection, and possible symptom of compulsive hoarding
* Clutter (marketing), numerous advertisements, a ...
. Its effects are slowing of speech which can result in increased fluency for people who clutter and also syllable awareness.
Effects in people who do not stutter
Studies that are more recent have looked at the effects of DAF in people who do not stutter to see what it can prove about the structure of the auditory and verbal pathways in the brain.
Indirect effects of delayed auditory feedback in people who do not stutter include a reduction in the rate of speech, an increase in intensity, and an increase in fundamental frequency that occur to overcome the effects of the feedback.
Direct effects include the repetition of syllables, mispronunciations, omissions, and omitted word endings. These direct effects are often referred to as “artificial stuttering."
With an individual who does not stutter, auditory feedback speech sounds are directed to the inner ear with a 0.001 second delay. In delayed auditory feedback, the delay is artificially disrupted.
Studies have found that in children ages 4–6 there is less disturbance of speech than in children ages 7–9 under a delay of 200 ms.
Younger children are maximally disrupted around 500 ms while older children around 400 ms. A 200 ms delay produces maximum disruption for adults. As the data collected from these studies indicate, the delay required for maximum disruption decreases with age. However, it increases again for older adults, to 400 ms.
Sex differences in DAF show no difference or indicate that men are generally more affected than women,
indicating that the feedback subsystems in the vocal monitor process could be different between the sexes.
In general, more rapid, fluent speakers are less affected by DAF than slower, less fluent speakers. Also, more rapid fluent speakers are maximally disrupted by a shorter delay time, while slower speakers are maximally disrupted under longer delay times.
Studies using computational modeling and functional magnetic resonance imaging (fMRI) have shown that the temporo-parietal regions function as a conscious self-monitoring system to support an automatic speech production system and that projections from auditory error cells in the posterior superior temporal cortex that go to motor correction cells in right frontal cortex mediate auditory feedback control of speech.
Effects in non-humans
Continuous delayed auditory feedback in Zebra finch songbirds caused them to change their song syllable timing, indicating that DAF can change the motor program of syllable timing generation during short periods of time in zebra finches, similar to the effects observed in humans.
References
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Sound
Anti-stuttering devices