Amblyaudia (amblyos- blunt; audia-hearing) is a term coined by Dr. Deborah Moncrieff to characterize a specific pattern of performance from dichotic listening tests. Dichotic listening tests are widely used to assess individuals for binaural integration, a type of auditory processing skill. During the tests, individuals are asked to identify different words presented simultaneously to the two ears. Normal listeners can identify the words fairly well and show a small difference between the two ears with one ear slightly dominant over the other. For the majority of listeners, this small difference is referred to as a "right-ear advantage" because their right ear performs slightly better than their left ear. But some normal individuals produce a "left-ear advantage" during dichotic tests and others perform at equal levels in the two ears. Amblyaudia is diagnosed when the scores from the two ears are significantly different with the individual's dominant ear score much higher than the score in the non-dominant ear Researchers interested in understanding the neurophysiological underpinnings of amblyaudia consider it to be a

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

based

hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory sci ...

disorder that may be inherited or that may result from auditory deprivation during critical periods of brain development. Individuals with amblyaudia have normal hearing sensitivity (in other words they hear soft sounds) but have difficulty hearing in noisy environments like restaurants or classrooms. Even in quiet environments, individuals with amblyaudia may fail to understand what they are hearing, especially if the information is new or complicated. Amblyaudia can be conceptualized as the auditory analog of the better known central

visual The visual system is the physiological basis of visual perception (the ability to detect and process light). The system detects, transduces and interprets information concerning light within the visible range to construct an image and buil ...

disorder

amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...

. The term “lazy ear” has been used to describe amblyaudia although it is currently not known whether it stems from deficits in the auditory periphery (middle ear or cochlea) or from other parts of the

auditory system The auditory system is the sensory system for the sense of hearing. It includes both the ear, sensory organs (the ears) and the auditory parts of the sensory system. System overview The outer ear funnels sound vibrations to the eardrum, incre ...

in the brain, or both. A characteristic of amblyaudia is suppression of activity in the non-dominant auditory pathway by activity in the dominant pathway which may be genetically determined and which could also be exacerbated by conditions throughout early development.

Symptoms and signs

Children with amblyaudia experience difficulties in speech perception, particularly in noisy environments, sound localization, and binaural unmasking (using interaural cues to hear better in noise) despite having normal hearing sensitivity (as indexed through pure tone audiometry). These symptoms may lead to difficulty attending to auditory information causing many to speculate that

language acquisition Language acquisition is the process by which humans acquire the capacity to perceive and comprehend language. In other words, it is how human beings gain the ability to be aware of language, to understand it, and to produce and use words and s ...

and academic achievement may be deleteriously affected in children with amblyaudia. A significant deficit in a child's ability to use and comprehend expressive language may be seen in children who lacked auditory stimulation throughout the critical periods of auditory system development. A child suffering from amblyaudia may have trouble in appropriate vocabulary comprehension and production and the use of past, present and future tenses. Amblyaudia has been diagnosed in many children with reported difficulties understanding and learning from listening and adjudicated adolescents are at a significantly high risk for amblyaudia (Moncrieff, et al., 2013, Seminars in Hearing).

Risk Factors

Families report the presence of amblyaudia in several individuals, suggesting that it may be genetic in nature. It is possible that abnormal auditory input during the first two years of life may increase a child's risk for amblyaudia, although the precise relationship between deprivation timing and development of amblyaudia is still unclear. Recurrent ear infections (

otitis media Otitis media is a group of Inflammation, inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pullin ...

) are the leading cause of temporary auditory deprivation in young children. During ear infection bouts, the quality of the signal that reaches the auditory regions of the brains of a subset of children with OM is degraded in both timing and magnitude. When this degradation is asymmetric (worse in one ear than the other) the binaural cues associated with

sound localization Sound localization is a listener's ability to identify the location or origin of a detected sound in direction and distance. The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system u ...

can also be degraded. Aural atresia (a closed external auditory canal) also causes temporary auditory deprivation in young children. Hearing can be restored to children with ear infections and aural atresia through surgical intervention (although ear infections will also resolve spontaneously). Nevertheless, children with histories of auditory deprivation secondary to these diseases can experience amblyaudia for years after their hearing has been restored.

Physiology

Amblyaudia is a deficit in binaural integration of environmental information entering the auditory system. It is a disorder related to

organization and function rather than what is typically considered a “hearing loss” (damage to the cochlea). It may be genetic or developmentally acquired or both. When animals are temporarily deprived of hearing from an early age, profound changes occur in the brain. Specifically, cell sizes in brainstem nuclei are reduced, the configuration of brainstem

dendrites A dendrite (from Greek δένδρον ''déndron'', "tree") or dendron is a branched cytoplasmic process that extends from a nerve cell that propagates the electrochemical stimulation received from other neural cells to the cell body, or soma ...

are altered and neurons respond in different ways to sounds presented to both the deprived and non-deprived ears. An electrophysiologic study demonstrated that children with amblyaudia (referred to then as a "left-ear deficit") were less able to process information from their non-dominant ears when competing information is arriving at their dominant ears. The N400-P800 complex showed a strong and highly correlated response from the dominant and non-dominant ears among normal children while the response from children with amblyaudia was uncorrelated and indicated an inability to separate information arriving at the non-dominant ear from the information arriving at the dominant ear. The same children also produced weaker fMRI responses from their non-dominant left ears when processing dichotic material in the scanner.

Diagnosis

A clinical diagnosis of amblyaudia is made following dichotic listening testing as part of an auditory processing evaluation. Clinicians are advised to use newly developed dichotic listening tests that provide normative cut-off scores for the listener's dominant and non-dominant ears. These are the Randomized Dichotic Digits Test and the Dichotic Words Test. Older dichotic listening tests that provide normative information for the right and left ears can be used to supplement these two tests for support of the diagnosis (). If performance across two or more dichotic listening tests is normal in the dominant ear and significantly below normal in the non-dominant ear, a diagnosis of amblyaudia can be made.

Treatments

A number of computer-based auditory training programs exist for children with generalized Auditory Processing Disorders (APD). In the visual system, it has been proven that adults with amblyopia can improve their

visual acuity Visual acuity (VA) commonly refers to the clarity of visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye ...

with targeted brain training programs (

perceptual learning Perceptual learning is learning better perception skills such as differentiating two musical tones from one another or categorizations of spatial and temporal patterns relevant to real-world expertise. Examples of this may include reading, seein ...

). A focused perceptual training protocol for children with amblyaudia called Auditory Rehabilitation for Interaural Asymmetry (ARIA) was developed in 2001 which has been found to improve dichotic listening performance in the non-dominant ear and enhance general listening skills.

References

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