The scope of this page is central auditory processing disorder (CAPD) in children and adults. Content is relevant to both developmental and acquired CAPD.
Central Auditory Processing Disorder Evidence Map for pertinent scientific evidence, expert opinion, and client/caregiver perspective.
Central auditory processing (CAP)—also seen in the literature as (central) auditory processing or auditory processing—is the perceptual processing of auditory information in the central auditory nervous system (CANS) and the neurobiological activity that underlies that processing and gives rise to electrophysiologic auditory potentials (American Speech-Language-Hearing Association [ASHA], 2005).
Knowledge of the neuroanatomy and physiology of the central auditory nervous system is essential for understanding and interpreting underlying processes and deficits. Medwetsky (2011) provides in-depth information on this topic.
CAP consists of mechanisms that preserve, refine, analyze, modify, organize, and interpret information from the auditory periphery. These mechanisms underlie the following skills:
- Auditory discrimination
- Temporal processing
- Auditory pattern recognition
- Temporal aspects of audition, including
- temporal integration;
- temporal resolution (e.g., temporal gap detection);
- temporal ordering; and
- temporal masking.
- Binaural processing
- Sound localization and lateralization
- Auditory performance with competing or degraded acoustic signals (including dichotic listening; ASHA, 2005)
Terms used to describe a processing disorder may vary based on the perspective of the professional describing the problem. Terms include, but are not limited to, "auditory processing disorder," "(central) auditory processing disorder," "language processing disorder," and "auditory information processing disorder."
ASHA uses the term Central Auditory Processing Disorder (CAPD) to refer to deficits in the neural processing of auditory information in the CANS not due to higher order language or cognition, as demonstrated by poor performance in one or more of the skills listed above (ASHA, 2005). Although sometimes difficult, careful differential diagnosis is important to the process of treatment planning.
- CAPD may lead to or be associated with difficulties in higher order language, learning, and communication functions.
- CAPD may coexist with other disorders (e.g., attention-deficit/hyperactivity disorder [ADHD], language impairment, and learning disability).
- CAPD is not due to peripheral hearing loss, which includes conductive hearing loss (i.e., outer or middle ear), sensorineural hearing loss at the level of the cochlea or auditory nerve, including auditory neuropathy and synaptopathy (i.e., hidden hearing
Professionals have adopted varying perspectives on the interpretation of CAPD (Cacace & McFarland, 2008; DeBonis & Moncrieff, 2008; De Wit et al., 2016; Friberg & McNamara, 2010; Jerger, 1998; McFarland & Cacace, 2006; Rees, 1973, 1981). Divergent perspectives among professionals reflect ongoing debate regarding how to define, assess, and treat auditory processing disorder.
Different viewpoints exist for a number of reasons, including the heterogeneity of symptoms, variations in the definition, the lack of a reference standard for diagnosis, the relationship between auditory perceptual deficits and language disorders, and the particular treatment approach(es) that follow from the diagnosis of CAPD (Kamhi, 2011; Moore, Rosen, Bamiou, Campbell, & Sirimanna, 2013; Vermiglio, 2014). Additional information providing an historical perspective on auditory processing disorder is available (DeBonis & Moncrieff, 2008; Richard, 2011).
Because of the heterogeneity of skills involved in auditory processing, some suggest that CAPD should be diagnosed by the specific deficit (e.g., difficulty processing signals in noise; difficulties with auditory discrimination, temporal processing, or binaural processing), rather than broadly as a CAPD (Vermiglio, 2016). Not all diagnoses of a CAPD represent a limitation for the individual (Dillon, Cameron, Glyde, Wilson, & Tomlin, 2012) or a condition that must be treated (Vermiglio, 2016).
There is general agreement that auditory perceptual abilities influence language development—particularly the pre-literacy skills—and that it can be difficult to separate the influence of auditory and language skills with regard to academic demands (Richard, 2012, 2013; Watson & Kidd, 2008). The act of processing speech is very complex and involves the engagement of auditory, cognitive, and language mechanisms, often simultaneously (Medwetsky, 2011).
Richard's (2013) continuum of processing includes both auditory processing and language processing. This continuum involves the following types of processing:
- Central auditory processing, which begins when the neural representation of acoustic signals are processed after they leave the cochlea and travel through the auditory nerve to the primary auditory cortices of the left and right hemispheres (Heschl's gyri).
- Phonemic processing, during which acoustic features of the signal are discriminated utilizing phonemic skills such as sound discrimination, blending, and segmenting.
- Linguistic processing, during which meaning is attached to the signal (begins at the level of Heschl's gyrus, expands to Wernicke's area, to the angular gyrus, and finally to the prefrontal and frontal cortex, where a response is planned, organized, and mediated).