Auditory processing disorder (APD)

In recent years, awareness of auditory processing disorder (APD) has increased. 

According to the American Speech-Language-Hearing Association (ASHA), auditory processing—also known as central auditory processing—refers to the perceptual processing of auditory information in the central auditory nervous system. 

When this process is impaired, a person may be diagnosed with auditory processing disorder, a condition that impacts their ability to understand spoken language. 

What is auditory processing disorder?

Auditory processing disorder (APD) and central auditory processing disorder (CAPD) are used interchangeably to describe a disorder in the processing of auditory information or—more simply put—the ability to interpret what you hear. 

This diagnosis refers to deficits in the neural processing of auditory information, but it does not result from higher order language disorders or cognitive difficulties.

An APD or CAPD diagnosis is given when testing confirms a disruption in the way an individual understands what they’re hearing in the absence of hearing loss. The APD ICD-10 code is H93.25.

Auditory processing disorder is easily confused with other disorders that can also impact a person's ability to attend, understand, and remember, so it is important to point out that APD is an auditory deficit that is not the result of other higher-order cognitive, language, or related disorders.

APD may be associated with language, learning, and communication difficulties and may co-occur with other disorders such as attention-deficit/hyperactivity disorder (ADHD), dyslexia, language delay or disorder, or learning disability. 

In these situations where diagnoses overlap, careful assessment is vital in determining the impacts of each diagnosis so that treatment for auditory processing disorder or central auditory processing disorder can be targeted appropriately.

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Auditory processing disorder symptoms

Auditory processing disorder or central auditory processing disorder often begin in childhood, but adults can also develop the conditions from certain diseases, a head injury, or even aging. 

There can be a wide range of auditory processing disorder symptoms, often overlapping with symptoms of other disorders.  

Symptoms of auditory processing disorder or central auditory processing disorder may include:

• Difficulty understanding speech, especially rapid speech or speech in noisy environments
• Difficulty following directions, especially multi-step directions
• Difficulty understanding abstract ideas such as jokes or figurative language
• Difficulty paying attention; easily distracted
• Difficulty localizing where a sound is coming from
• Misperceiving words or sounds
• Frequent requests for repetition
• Academic difficulties impacting the areas of reading, spelling, and writing as compared to peers
• Delayed or inappropriate responses during conversation

Types of auditory processing disorders

While auditory processing disorder is a single diagnosis, the resulting difficulties can be broken down into five subtypes and some people may experience more than one type: 

Hypersensitivity 

Hypersensitivity to sound is often diagnosed as misophonia in which someone has adverse physical reactions to sounds (e.g., becoming nauseated by the sound of chewing). 

Another hypersensitivity could be hyperacusis, which is characterized by a sensitivity to sounds (e.g., white noise can be deafening).

Decoding

Decoding difficulties impact the ability to make sense of spoken language. Sounds are heard, but the brain does not process them as words.

Integration

Integration difficulties impact the ability to complete multiple tasks while listening. For example, writing notes while listening to someone speak or having a conversation while typing may be difficult.

Prosodic

Prosodic difficulties refer to trouble interpreting tone, inflection, and implied meaning. For example, a question and exclamation may be processed similarly. This subtype may also impact the ability to comprehend figurative language that is more abstract than literal. In addition, those with this subtype of APD may have monotone speech.

Organizational

Organizational difficulties are characterized by not recalling information in a specific order or having difficulty recalling verbal information in noisy environments. This subtype impacts the ability to organize incoming spoken language.

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Auditory processing disorder causes

While the exact auditory processing disorder causes are not always known, the etiology may be linked to a specific lesion or disorder. 

Causes may include:

• Genetic conditions
• Neurological disorders, diseases, or damage
• Otologic disorders, diseases, or injury (e.g., recurring otitis media)
• Prenatal factors such as anoxia/hypoxia, cytomegalovirus, hyperbilirubinemia, low birth weight, prematurity, or prenatal drug exposure

There is some professional disagreement as to what an auditory processing disorder diagnosis means.

According to ASHA, there is currently no reference standard for diagnosing auditory processing disorder. The presentation is heterogenous, and symptoms frequently overlap with language and other disorders, further complicating the diagnostic process. 

As a result, professionals have differing viewpoints on APD. Some believe auditory processing disorder may indicate a broader language-based difficulty that requires language therapy. 

Others suggest that APD be diagnosed by a specific deficit (e.g., difficulty processing signals in noise or difficulty with binaural processing). 

In a 2011 research study, Alan G. Kamhi considered whether auditory processing disorder is truly a distinct clinical entity or whether auditory problems should be viewed as a processing deficit that may occur with various developmental disorders. He concluded that because there is no evidence that auditory interventions provide therapeutic benefit, clinicians should treat children who have been diagnosed with central auditory processing disorder the same way they treat children who have been diagnosed with language and learning disabilities—through goals targeted at speech, language, literacy, and knowledge.

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Central auditory processing disorder testing

An audiologist provides an official diagnosis of auditory processing disorder or central auditory processing disorder . However, a collaborative team including both audiologists and speech-language pathologists (SLPs) can ease the evaluation process, ensuring that clear areas of deficits are discovered. 

Working together, both professionals can determine whether an overlapping language disorder exists and whether the client has APD versus a language and/or a phonological processing disorder. 

First, professionals should administer a screening to identify whether a client requires a comprehensive evaluation for auditory processing disorder. 

These protocols may include auditory processing disorder screening tests, a combination of tests of auditory processing skills, and/or observational tools. Questionnaires and checklists can provide an overview of auditory abilities related to academic achievement, listening skills, and communication. 

As part of the evaluation process, clinicians should also take a full case history. 

This includes the following information:

• Prenatal and medical history, including otologic and neurologic history
• Genetic testing results
• Hearing health history
• Family health and hearing history
• Coexisting disabilities
• Cognitive and communication status
• Speech/language, reading, and social skills status
• Educational and/or occupational status
• Auditory and behavioral complaints

According to ASHA, one thing to keep in mind when assessing someone for auditory processing disorder is that variations in social communication norms—meaning differences in how people communicate depending on factors such as cultural background—or the use of multiple languages may falsely indicate a disturbance in auditory processing. Taking a comprehensive history can be helpful in avoiding misdiagnoses.

A comprehensive assessment can highlight areas in which challenges exist, therefore making it easier to determine goals. 

A 2017 article in The ASHA Leader advised SLPs to target language/literacy skills with those diagnosed with auditory processing disorder because research indicates language processing difficulties typically indicate broader language-based deficits. For example, if the client has difficulty recognizing speech in noise, therapy may focus on improving their knowledge of specific vocabulary. 

Audiological testing includes:

• Audiologic evaluation of the peripheral auditory system by an audiologist: This will diagnose or rule out conductive, sensorineural, and mixed hearing loss, as well as auditory neuropathy spectrum disorder.
• Audiologic/speech evaluation of the central auditory system: 
• Auditory discrimination tests: These tests assess someone’s ability to differentiate similar acoustic stimuli that differ in frequency, intensity, and/or temporal parameters. 
• Auditory temporal processing and patterning tests: These tests evaluate a person’s ability to perceive and interpret the order or pattern of sounds over time. 
• Dichotic speech tests: These tests provide insight on how the brain processes sound from both ears, assessing someone’s ability to separate and integrate auditory stimuli presented simultaneously to both ears.
• Monaural low-redundancy speech tests: These tests assess the recognition of degraded speech stimuli presented to one ear at a time, including speech in noise, speech in competition, low-pass filtered speech, or rapid speech.
• Binaural interaction tests: These tests evaluate how well the auditory system processes sounds presented to both ears.

While an audiologist provides the official diagnosis, SLPs can administer a variety of assessments to identify potential areas of concern. 

Some of these tests include the SCAN-3:C (Screening Test for Auditory Processing Disorders in Children), the Auditory Skills Assessment (ASA), the Multiple Auditory Processing Assessment (MAPA), and various dichotic listening tasks. 

Including language-based assessments as part of the evaluation process is also helpful in determining specific areas of deficit to target in therapy. 

The takeaway

Auditory processing disorder causes a difficulty in the processing of auditory information. Audiologists and SLPs work together during the APD evaluation process. 

While professionals continue to disagree on whether this diagnosis is its own entity, a comprehensive evaluation and goals that target language and literacy skills can provide the best therapy outcome.

Sources

• Aristidou, I. L. and Hohman, M. H. (2023). Central Auditory Processing Disorder. https://www.ncbi.nlm.nih.gov/books/NBK587357/#:~:text=CAPD%20is%20primarily%20a%20condition%20that%20affects,disorder%20(ADHD)%2C%20and%20autism%20spectrum%20disorder%20(ASD). 
• Auditory Processing Disorder. (2023). https://my.clevelandclinic.org/health/diseases/24938-auditory-processing-disorder 
• Central Auditory Processing Disorder. (2024). https://www.asha.org/practice-portal/clinical-topics/central-auditory-processing-disorder/?srsltid=AfmBOopvhAAzR9qVycYjEQhATxkEoh_KEY-n-ewBuQb5UXL-Bbm3LtRZ
• Kamhi, Alan G. (2011). What Speech-Language Pathologists Need to Know About Auditory Processing Disorder. https://pubs.asha.org/doi/10.1044/0161-1461(2010/10-0004)
• Understanding Auditory Processing Disorders in Children. (2024). https://www.asha.org/public/hearing/understanding-auditory-processing-disorders-in-children/
• What is Auditory Processing Disorder? (2024). https://montefioreeinstein.org/neuroscience/neurological-conditions/intellectual-developmental-disorders/auditory-processing-disorder

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