Auditory feedback (AF) is an aid used by humans to control

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 v ...

and

singing Singing is the act of creating musical sounds with the voice. A person who sings is called a singer, artist or vocalist (in jazz and/or popular music). Singers perform music ( arias, recitatives, songs, etc.) that can be sung with or ...

by helping the individual verify whether the current production of speech or singing is in accordance with his acoustic-auditory intention. This process is possible through what is known as the auditory feedback loop, a three-part cycle that allows individuals to first speak, then listen to what they have said, and lastly, correct it when necessary. From the viewpoint of movement sciences and

neuroscience Neuroscience is the science, scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a Multidisciplinary approach, multidisciplinary science that combines physiology, an ...

s, the acoustic-auditory speech signal can be interpreted as the result of movements (skilled actions) of speech articulators (the lower jaw, lips, tongue, etc.). Auditory feedback can hence be inferred as a feedback mechanism controlling skilled actions in the same way that visual feedback controls limb movements (e.g. reaching movements).

Speech

Auditory feedback allows one to monitor their speech and rectify production errors quickly when they identify one, making it an important component of fluent speech productions. The role of auditory feedback on speech motor control is often investigated by exposing participants to frequency-altered feedback. Inducing brief and unpredictable changes in the frequency of their auditory feedback has consistently been shown to induce a "pitch-shift reflex", which suggests that this reflex aids in stabilizing voice frequency around the desired target. However, due to the fact that auditory feedback needs more than 100 milliseconds before a correction occurs at the production level, it is a slow correction mechanism in comparison with the duration (or production time) of speech sounds (vowels or consonants). Thus, auditory feedback is too slow to correct the production of a speech sound in real-time. Nonetheless, it has been shown that auditory feedback is capable of changing speech-sound production over a series of trials (i.e. adaptation by relearning; see e.g. perturbation experiments done with the DIVA model:

neurocomputational speech processing Neurocomputational speech processing is computer-simulation of speech production and speech perception by referring to the natural neuronal processes of speech production and speech perception, as they occur in the human nervous system (central ner ...

). 10 minutes is typically sufficient for a nearly-full adaptation. Research has also shown that auditory linguistic prompts resulted in greater correction to acoustic perturbations than non-linguistic prompts, reflecting the decrease in accepted variance for intended speech when external linguistic templates are available to the speaker.

Speech Acquisition and Development

Auditory feedback is an important aid during

speech acquisition Speech acquisition focuses on the development of vocal, acoustic and oral language by a child. This includes motor planning and execution, pronunciation, phonological and articulation patterns (as opposed to content and grammar which is language). ...

toddler A toddler is a child approximately 12 to 36 months old, though definitions vary. The toddler years are a time of great cognitive, emotional and social development. The word is derived from "to toddle", which means to walk unsteadily, like a child ...

s, by providing the child with information about speech outcomes that are used to pick-up and eventually hone speech motor planning processes. Auditory inputs are typically produced by a communication partner (e.g. caretaker) and heard by the toddler, who subsequently tries to imitate them. Children as young as the age of four have demonstrated the ability to adapt speech motor patterns to perceived changes in vowel auditory feedback, which enables them to maintain the accuracy of their speech output. However, children's speech motor adaption abilities are not fully optimised due to their limited auditory perceptual skills. Thus, improvements in children's ability to perceive relevant acoustic property will usually be followed by an improvement in their speech adaption performance. Individuals who are born deaf often fail to acquire fluent speech, further reinforcing how auditory feedback plays a crucial role in speech acquisition and development. Delayed auditory feedback experiments indicate that auditory feedback is important during speech production, even in adults. It has been shown that severe disfluencies in speech occur when the timing of voice feedback is delayed for a normal speaker. Individuals who become deaf post-lingually and are unable to receive vocal feedback anymore also typically experience a deterioration in speech quality, highlighting the importance of auditory feedback in speech formation throughout one's lifetime.

Impacts on speech disorders

Stuttering

Stuttering is said to be due to ineffective monitoring of auditory feedback, mainly caused by a deficit in the cortical auditory system modulation during speech planning. When fluent speakers detect a sudden irregularity in a specific acoustic parameter of their auditory feedback, they are able to instantly correct the error in their speech production. Individuals who stutter, on the other hand, are found to have weaker-than-normal abilities to correct such errors. Individuals that stutter hence demonstrate ineffective auditory comparisons of desired speech movements, as compared to fluent speakers. Delayed auditory feedback has been found to be an effective treatment for some individuals who stutter, since extending the time between speech and auditory perception allows for more time to process and correct errors.

Apraxia of speech

It is posited that individuals with

apraxia of speech Apraxia of speech (AOS), also called verbal apraxia, is a speech sound disorder affecting an individual's ability to translate conscious speech plans into motor plans, which results in limited and difficult speech ability. By the definition of a ...

have weak

feedforward Feedforward is the provision of context of what one wants to communicate prior to that communication. In purposeful activity, feedforward creates an expectation which the actor anticipates. When expected experience occurs, this provides confirmato ...

programs, which results in the disfluencies of their speech. These individuals hence develop a heavy reliance on auditory feedback to minimize and repair speech errors even in later stages of their lives, whilst fluent speakers easily transitions from feedback dependent to feedforward-dominant. This is not ideal since heavy reliance on mostly auditory feedback is said to be inefficient for the production of rapid and accurate speech. Auditory masking has been found to decrease disfluency duration and increase vocal intensity as well as syllable rate in some individuals with apraxia of speech. Since apraxia of speech is said to be due to weak feedforward programs and high dependence on auditory feedback, auditory masking can be reasoned to increase fluency by decreasing the frequency of a speaker attending auditorily to speech errors, and hence reducing the likelihood of disfluency-generating corrections.

Impacts on Visually Impaired individuals

Enhanced auditory processing can be observed in individuals with

visual impairment Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

, who partially compensate for their lack of vision with greater sensitivity in their other sensories. Their increased sensitivity to auditory feedback allows them to demonstrate impressive spatial awareness despite their lack of sight.

Desktop Assistance

Studies have shown that when vision is no longer the primary source for obtaining information, focus shifts from vision to hearing in the desktop environment. Currently, there are assistive technologies such as

screen reader A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to people who are blind, and are useful to people who are visually impaired, illiterate, or ...

s, which aids visually impaired individuals in obtaining information on their desktop screens via auditory feedback (E.g. JAWS). The assistance can come in the form of either speech based auditory feedback or non-speech based auditory feedback. Speech based interfaces are based on human speech, whilst non-speech based interfaces are based on environmental sounds such as music or artificial sound effects. For the visually impaired, sole reliance on speech based auditory feedback imposes a heavier cognitive load which is irritating for users. In contrast, non-speech auditory feedback is pleasant and conveys information more quickly, but lacks detailed information in their conveyance and training is required to understand the cues. Hence, the most ideal interface currently is adaptive auditory feedback, which automatically transitions between speech and non-speech cues based on the user state. Such an interface has been found to be more comfortable and generates higher satisfaction amongst visually impaired users.

Impacts on other disorders

Graphomotor learning in writing disorders

A trial was conducted to explore whether auditory feedback had an influence on learning how to write. It was found that in adults, auditory feedback enabled the writer to better discern their writing motions. This resulted in an increase in flow and quickness of writing when using sounds to learn the writing of new characters. Subsequent studies then tested the use of auditory feedback as an aid for children with

dysgraphia Dysgraphia is a learning disability of written expression, which affects the ability to write, primarily handwriting, but also coherence. It is a specific learning disability (SLD) as well as a transcription disability, meaning that it is a writ ...

to learn how to write. It was found that after multiple sittings of using auditory feedback while writing, children could write more smoothly, rapidly and clearly. Products based on auditory feedback principles have been invented to aid individuals with such writing disorders. Children with speech disorders can also benefit from such products. For example, a headphone called Forbrain uses a bone conductor and a series of dynamic filters to correct the perception of one's own voice. This improves concentration, attention, speech, coordination, and other sensory functions. It was awarded by the BETT Show in 2015 in the category "ICT Special Educational Needs Solutions".

Motor learning in movement disorders

Patients with

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sens ...

have little walking capability, due to limitations of their

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

. Auditory feedback in the form of periodic audio signals was found to have a significant improvement on the

gait Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...

of patients, with several explanations proposed. One model argues that auditory feedback acts as an additional information channel for the motor systems, thereby decreasing the onset of motor faults and refining the gait of patients. Another model posits that audio signals influence the gait of patients by directing motion patterns, such as heel strike timings. By wearing a device that provides immediate auditory feedback on the quality of one's gait, children with cerebral palsy learned to set down their feet in proper ways that avoided the sounds created when negative gaits were detected.

Social interaction and motor coordination learning in behavioural disorders

The use of an auditory feedback-based treatment is found to have improved on the social interaction, mimicking and coordination skills of children with

autism spectrum disorder The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

. This is achieved through a software which uses sensors to track the body motions of children. Each gesture made will activate a voice recording articulating pieces of sentences. Children then have to reorder these sentence pieces to form a storyline. Different indicators of coordination such as motion quantity and speed were also recorded to keep track of the child's improvement through these auditory cues.

Impacts on Music Performance

Instrument Performance

Auditory feedback is important in the picking up of a new musical piece. By exposing beginner piano players to irregular auditory feedback, they make more mistakes as compared to those who are given logical and anticipatable auditory feedback. Learning in the presence of auditory feedback also improved one's recollection of the musical piece. However, multiple studies have shown that even without auditory feedback, there is not much disturbance to the performance of seasoned musicians. In the absence or delay of auditory feedback, musicians turn to

auditory imagery Auditory imagery is a form of mental imagery that is used to organize and analyze sounds when there is no external auditory stimulus present. This form of imagery is broken up into a couple of auditory modalities such as verbal imagery or musical i ...

to direct their performance. Other forms of feedback can also be used in compensation instead, such as visual feedback where musicians look at their hands to lead their performance. Major disturbances were only seen in the area of pedaling, where results have shown that pianists were prone to stepping the pedal less often in the absence of auditory feedback.

Singing

The importance of auditory feedback in the case of human

is reviewed by Howell. In the context of singing, it is important for singers to maintain pitch accuracy, even when they are drowned out by orchestral accompaniment or by fellow singers. Many studies have looked into the effects of both external auditory feedback and

proprioception Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...

(also known as internal feedback) on pitch control. It has been found that external auditory feedback is crucial in maintaining pitch accuracy, especially for adults without voice training. This is further supported by recent research which revealed how non-professional singers show lower pitch accuracy when they receive lesser auditory feedback. However, the research also highlighted how the pitch of professional singers remains almost unaffected by auditory feedback since they are able to rely on their internal feedback after years of training.

Bird songs

The role of auditory feedback in the learning and production of

bird-song Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs (relatively complex vocalizations) are distinguished by func ...

has been studied in several research papers. It has been found that songbirds rely on auditory feedback to compare the sounds that they make with inborn tunes or songs that they memorize from others. Numerous studies have shown that without the ability to hear themselves, songbirds develop erratic songs or show a deterioration in the songs that they sing after experiencing

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken l ...

. Several scientific models have been put forward to explain the worsening of birdsongs after the loss of hearing. (E.g. see Brainard and Doupe's (2000) error adjustment channel in the anterior forebrain: auditory feedback in birdsong learning). However, the decline of birdsong quality can vary greatly between different demographics. For example, other studies have found the songs of older songbirds remained consistent, or had a slower rate of deterioration after going deaf. Some researchers have attributed to songbirds learning how to use other forms of non-auditory feedback such as

sensory information A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system re ...

to maintain the quality of their songs. This process is called

sensory-motor coupling Sensory-motor coupling is the coupling or integration of the sensory system and motor system. Sensorimotor integration is not a static process. For a given stimulus, there is no one single motor command. "Neural responses at almost every stage of a ...

. Others have argued that older songbirds have a longer access to auditory feedback to learn their songs, which results in more practice and thus more stable production of songs even after deafening.

References

{{Reflist Hearing Speech