Auditory processing disorder (APD) is a deficit in the processing of information that is specific to the auditory modality.1 APD typically involves deficits in dichotic listening, selective attention, and temporal processing. APD has been observed in diverse clinical populations, including those where central nervous system pathology or neuromorphologic disorder is suspected (e.g., developmental language disorder, dyslexia, learning disability, attention deficit disorder) and those where evidence of central nervous system pathology is clear (e.g., aphasia, multiple sclerosis, epilepsy, traumatic brain injury, Alzheimer's disease).2
This co-morbidity occurs because all auditory tasks, from pure-tone perception to spoken language processing, are influenced by higher-level, non-modality specific factors such as attention, learning, motivation, and decision processes.3–6 Moreover, there is a complex arrangement of shared physiologic and neurologic networks across these processes and mechanisms.7–11
Given the heterogeneous nature of APD and the range of listening and learning deficits that often accompany it, comprehensive evaluation requires a multidisciplinary team approach. APD is a perceptual disorder diagnosed by the audiologist on the basis of an extensive audiologic evaluation that employs challenging auditory tasks involving sensitized stimuli (e.g., speech presented in dichotic competition, filtered or time-compressed speech, etc.). Currently, diagnosis of APD is based on the outcomes of auditory behavioral tests, supplemented by electroacoustic and electrophysiologic measures.1
DIFFERENTIATION REQUIRES MANY TESTS
To more definitively differentiate perceptual, modality-specific APD from multimodal perceptual deficits (i.e., polysensory deficits occurring in multiple sensory modalities), one must compare similar behavioral tasks in at least two modalities.12 And, to differentiate APD from non-perceptual cognitive deficits (i.e., supramodal deficits that are independent of sensory modality), one must examine cognitive and executive functions. The multidisciplinary team also must evaluate language and psychoeducational achievement to identify associated conditions, clarify the functional impact of the APD, and plan and implement therapy.
Analogous testing in the visual modality has been recommended as an optional procedure in the APD diagnostic test battery.1 It is important that audiologists either administer these additional tests or refer patients for analogous testing in the visual domain. These tests might include behavioral tests and event-related potentials.13,14 Auditory and visual continuous performance tests (CPTs) can be used to examine both multimodality sensory function and executive control (i.e., response inhibition). As such, CPTs can provide information to assist in the differential diagnosis of APD and attention deficit hyperactivity disorder (ADHD).15 Neuroimaging also offers great promise for differential diagnosis.13
Given the overlapping symptomatology across diverse clinical populations and the range of listening and learning deficits associated with APD, comprehensive evaluation of patients suspected of APD must be multidisciplinary. Comparing analogous tasks across sensory modalities should help differentiate auditory-specific, perceptual modality deficits (APD) from supramodal, cognitive deficits and from multisensory deficits.1,12,16
1. Jerger J, Musiek FE: Report of the consensus conference on the diagnosis of auditory processing disorders in school-aged children. JAAA
2. Chermak GD, Musiek FE: Central Auditory Processing Disorders: New Perspectives
. San Diego: Singular Publishing Group, 1997.
3. Denckla MB: A theory and model of executive function: A neuropsychological perspective. In Lyon GR, Krasnegor NA, eds. Attention, Memory, and Executive Function
. Baltimore: Paul H. Brookes, 1996: 263–278.
4. Fitch RH, Miller S, Tallal P: Neurobiology of speech perception. Neurosci
5. Hasegawa RP, Blitz AM, Geller NL, Goldberg ME: Neurons in monkey prefrontal cortex that track past or predict future performance. Science
6. Silman S, Silverman CA, Emmer MB: Central auditory processing disorders and reduced motivation: Three case studies. JAAA
7. Poremba A, Saunders RC, Crane AM, et al.: Functional mapping of the primate auditory system. Science
8. Crosson BA: Subcortical Functions in Language and Memory
. New York: Guilford, 1992.
9. Phillips DP: Central auditory processing: A view from auditory neuroscience. Am J Otol
10. Phillips DP: Auditory gap detection, perceptual channels, and temporal resolution in speech perception. JAAA
11. Salvi RJ, Lockwood AH, Frisina RD, et al.: PET imaging of the normal human auditory system: Responses to speech in quiet and in background noise. Hear Res
12. McFarland DJ, Cacace AT: Modality specificity as a criterion for diagnosing central auditory processing disorders. AJA
13. Jerger J, Thibodeau L, Martin J, et al.: Behavioral and electrophysiologic evidence of auditory processing disorder: A twin study. JAAA
14. McFarland DJ, Cacace AT: Modality specificity of auditory and visual pattern recognition: Implications for the assessment of central auditory processing disorders. Audiology
15. Riccio CA, Reynolds CR, Lowe PA: Clinical Applications of Continuous Performance Tests
. New York: John Wiley & Sons, 2001.
16. Chermak GD, Hall J, Musiek FE: Differential diagnosis and management of central auditory processing disorder and attention deficit hyperactivity disorder. JAAA