Auditory Processing Disorder
The brain may have problems processing auditory information resulting in an auditory processing disorder, previously called central auditory processing disorder. Auditory processing disorder is a generic term for all hearing disorders that have a mismatch between the normal function of the peripheral auditory organs and structures and the brain’s ability to interpret or discriminate sounds. It is a heterogeneous group of auditory-specific disorders exhibiting one or more deficits in (1) auditory processing of sound localization and lateralization, (2) discriminating sounds, (3) auditory pattern recognition, and (4) temporal resolution, masking, integration, and ordering. Furthermore, a person with an auditory processing disorder will have difficulty in picking out sounds and/or words in noisy environments.
Anatomy and Physiology
Persons with an auditory processing disorder generally have normal anatomical structures of the outer, middle, and inner ear. These structures also function normally for the sense of hearing. It is the structures in the brain that have problems integrating the auditory signal into perceived sounds. Thus, these patients have problems in recognizing sounds as well as interpreting what the sound is, particularly when there are background noises. These difficulties are magnified when identifying speech sounds. Persons with auditory processing disorder generally have problems understanding rapid speech or degraded speech and following oral instructions. To compensate for the disorder, individuals may try to fill in the missing words.
Auditory processing disorder is usually noticed in young infants and children. Caregivers and teachers may see that the child is regressing during development, particularly in language comprehension. Studies have shown that causes of auditory processing disorder are ectopic cells in the primary auditory cortex and genetic seizure disorders, to name a few. The primary auditory cortex (located in the left temporal lobe) is essential for performing basic and higher functions in hearing. Ectopic or misplaced cells in the primary auditory cortex will have malformations in circuitry, resulting in abnormal processing. Furthermore, function of the primary auditory cortex depends on the sounds encountered early in life, and if the circuitry is not properly working, this can result in an auditory processing disorder. Other causes have been associated with autosomal dominant epilepsy or seizures that affect the left temporal lobe, resulting in auditory processing problems.
There are several disorders that have deficits similar to those of auditory processing disorder. Thus, it can be difficult to properly diagnose. The most common similar disorders are language processing disorders as well as attention deficit hyperactivity disorder (ADHD). To obtain a diagnosis, speech-language pathologists, psychologists, health care providers, and teachers all work together to perform a comprehensive assessment. Diagnosis requires specific outcomes of behavioral tests, measuring brainstem auditory evoked potentials (BAEP), and auditory tests. However, it can be difficult to determine auditory processing disorder in infants and children as they have limited language ability, may be unable to pay attention to the test, and may not be able to cope with testing demands.
To date, interventions for persons with auditory processing disorder include improving (1) the quality of the acoustic signal—such as ensuring that speech is clear and not degraded, (2) the listening environment by decreasing background noise, (3) auditory skills, and (4) language skills.
Jennifer L. Hellier
See also: Auditory System; Auditory Threshold; Brainstem Auditory Evoked Potentials; Tonotopic Map; Vestibulocochlear Nerve
Chermak, Gail D. (2002). Deciphering auditory processing disorders in children. Otolaryngologic Clinics of North America, 35(4), 733—749.
Micallef, Lara A. (2015). Auditory processing disorder (APD): Progress in diagnostics so far. A mini-review on imaging techniques. Journal of International Advanced Otology, 11(3), 257—261. http://dx.doi.org/10.5152/iao.2015.1009
Vermiglio, Andrew J. (2016). On diagnostic accuracy in audiology: Central site of lesion and central auditory processing disorder studies. Journal of the American Academy of Audiology, 27(2), 141—156. http://dx.doi.org/10.3766/jaaa.15079