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(Central) Auditory Processing Disorders: Overview and Amplification IssuesDouglas L. Beck Au.D. Teri James Bellis Ph.D. Abstract: (Central) Auditory Processing Disorders ([C]APDs) are tremendously challenging. Each patient seeking diagnosis and treatment has a unique background, their own individual listening needs, desires, observations and complaints, facilitating a vast spectrum of aural rehabilitative needs and treatment plans. (C)APDs occur in pediatric and adult patients with normal hearing and in those with hearing loss. Although audiologists are the professionals qualified to diagnose (C)APD, a multidisciplinary team-based approach to (C)APD differential diagnosis and treatment is advocated, particularly regarding the pediatric population. This article will serve as a brief review of (C)APD with specific attention to the use of amplification for patients with (C)APD and hearing loss. Introduction: A Central Auditory Processing Disorder is defined as "a deficit in the perceptual processing of auditory stimuli and the neurobiological activity underlying that processing" (ASHA, 2005a, p. 2). (C)APD likely arises from abnormal neural representation of speech and non-speech sounds in the central auditory nervous system (CANS) and the (C)APD may occur in pediatric and adult patients with normal hearing or may co-exist with, or occur secondary to, peripheral hearing loss. (C)APD leads to difficulties in various auditory functions that are important for listening and comprehending spoken language, especially in noisy backgrounds. As such, (C)APD deficits may include difficulty with lateralization, localization, auditory discrimination, auditory pattern recognition, other temporal processing deficits, and more (ASHA, 2005a). Generally, patients with (C)APD are children presenting with listening problems in the classroom and difficulty in academic pursuits. (C)APD may be associated with learning disorders especially in the areas of reading, spelling, articulation problems, difficulty following directions and significant challenges regarding communicating and comprehending (Bellis, 2002, 2003a). (C)APD is more common in boys than girls and is even more common in children with a significant history of otitis media (Katz & Wilde, 1994). Roughly 7% of children are estimated to have (C)APD (Bamiou, Musiek and Luxon, 2001). (C)APD must be diagnosed using tools previously shown to have validity for identification of CANS dysfunction (ASHA, 2005a). Unfortunately, diagnostic tools currently available do not allow (C)APD to be evaluated in children below 7 years of age, secondary to variability in the development of the brain and central nervous system. Other common disorders can mimic or co-exist with (C)APD. For example, attention deficit hyperactivity disorder (ADHD), autism, language processing disorder, and various cognitive disorders may lead to listening behaviors similar to those of (C)APD. However, the diagnosis of (C)APD is not appropriate when listening difficulties arise from, or are due to, higher-order, pan-sensory or global disorders, unless concomitant dysfunction in the CANS can be demonstrated (ASHA, 2005a). Therefore, with respect to pediatric applications, a multidisciplinary team-based approach involving the audiologist, parent(s), physician, speech-language pathologist, teacher, school psychologist, and possibly others is critical to assure all behaviors, actions, and observations have been addressed and considered, prior to arriving at a differential diagnosis (ASHA, 2005a; Bellis, 2002, 2003a). Diagnostic Issues: (C)APD is indeed, sometimes difficult to diagnose. Test results can be ambiguous, unique or difficult to interpret. Because (C)APD often cannot be seen on neuron-imaging tests (for example MRI, CT, etc.) some professionals have argued the disorder may not exist as an exclusive entity. However, recent scientific findings have clearly demonstrated the reality of (C)APD and its existence can no longer be doubted (ASHA 2005a, b; Jerger & Musiek, 2000; see Bellis, 2002, 2003a and see Chermak & Musiek 2006a, b for reviews). Indeed, patients with (C)APD exhibit extreme difficulty with audition, which may negatively impact their educational, social and work situations -- and these deficits cannot be accounted for by hearing loss or other factors. Results of central auditory testing in these individuals reveal patterns of findings known to be associated with dysfunction in the CANS. Further, neural representation of sound within the brains of people with (C)APD, often is different from that of the normal population. Treatment Issues: Jerger and Musiek (2002) noted that the efficacy of a given treatment is best determined by a randomized, double-blind trial. Unfortunately, we do not have such data related to the majority of treatment paradigms for (C)APD. Nonetheless, neuro-plasticity research provides a solid scientific foundation upon which to base several general principles of (C)APD intervention. First, there is no "one size fits all" approach to (C)APD treatment. Rather, treatment should be individualized and deficit-specific. Second, intervention for (C)APD should focus on bottom-up (e.g., auditory training, acoustic signal enhancement) and top-down (e.g., central resources training) activities. Finally, intervention for (C)APD should include three primary components (ASHA, 2005a; see Bellis, 2002, 2003a and Chermak & Musiek, 2006b for reviews):
(C)APD and FM Technology: As noted above, improving access to the auditory signal is a key component of (C)APD intervention for many individuals. One of the most effective ways to accomplish improved access is by using an FM system. Beck, Doty-Tamasula and Sexton (2006) noted three distinct advantages provided via FM. FM reduces the deleterious effects of distance, reverberation and noise. As a result, a cleaner auditory signal with an improved signal-to-noise ratio is presented to the listener, making the listening task easier, less stressful and more enjoyable. Smaldino and Crandell (2000) suggested that for children who have difficulty attending to the teacher's voice in a noisy classroom, technology designed to maximize the signal-to-noise ratio may be required. The authors reported normally hearing children require a 10 dB better signal-to-noise ratio, than do adults, to perform at the same level. Further, children with hearing loss often require an additional 15 dB signal-to-noise ratio to achieve the same results. Weihing (2005) reported that regardless of age, most people, even those with extremely poor unaided auditory performance, experienced vast improvements (nearly 100%) in auditory performance, simply through use of an FM system. Although Weihing focused on individuals with hearing loss rather than those with (C)APD, the report underscored the importance of signal-to-noise ratio as a major component of listening success. Although the multiplicity of advantages associated with FM are vast, FM and other hearing technologies may not be indicated or recommended for all people diagnosed with (C)APD. Rather, the decision to employ such technologies should be highly individualized with consideration for people (patient, teacher, and others), the overall classroom or other communicative acoustic environment (ANSI, 2002; see Crandell & Smaldino, 2004 for review) and the time and place of the communicative event. Importantly, efficacy of treatment, peripheral hearing, and hearing instrument use must be monitored carefully with regular evaluation and (C)APD and Hearing Aids Regarding fitting hearing aids on children with (C)APD, one must consider the needs of hearing-impaired children as well as those of normally hearing children. (C)APD can co-exist with, or occur secondary to, peripheral hearing loss. AAA (2003) suggested that special consideration be given to hearing-aid amplification when fitting children with unilateral, mild, minimal, or profound hearing loss and auditory neuropathy. In particular, based on the probability for children with mild/minimal hearing loss to experience academic difficulties, these children "should be considered candidates for amplification and/or personal FM.or soundfield use in school" (p. 4). Indeed, if a child has normal peripheral hearing sensitivity and (C)APD (or auditory neuropathy, or unilateral hearing impairment) hearing-aid amplification with appropriate monitoring of hearing sensitivity and a cautious approach to the hearing aid output may be warranted (AAA, 2003). Regarding older adults, it should be recognized that (C)APD may affect up to 75% of the elderly population and may compromise success with hearing aids, particularly regarding binaural hearing aids (Bellis, 2003b; see Bellis, 2006 for a review). Of course, hearing aid fittings impact more than hearing; they impact the central nervous system. Pichora-Fuller and Singh (2006) suggested that rehabilitative audiology for aged patients should acknowledge and perhaps maximize "compensatory brain reorganization" as patients acclimatize to modern hearing aid fittings. Cognition and audition appear related in at least two ways. First, cognitive performance appears to worsen as hearing loss and auditory perceptions decrease. Second, cognitive ability appears to impact hearing aid performance (see Pichora-Fuller and Singh). Pichora-Fuller and Singh (2006) suggested working memory capacity as a likely bridge between cognition and audition, with due consideration to hearing aid fittings as the conduit which fosters these changes. Additionally, directed auditory training focused on specific central auditory skills, including inter-hemispheric transfer of auditory information and other focused auditory training activities may assist in maximizing success with binaural amplification in elderly patients (Bellis, 2003b; 2006; Sweetow & Hendersen-Sabes, 2004). Summary: (C)APD is a disorder of perceptual processing of auditory signals in the CANS. (C)APD impacts children and adults and can co-exist with hearing loss and other disorders. Intervention for (C)APD is highly dependent on accurate diagnosis and should focus on improving the acoustic and communicative environment, strengthening central resources to compensate for the disorder and directly stimulating the CANS via auditory training. One of the common primary treatment goals for children and adults diagnosed with (C)APD is the improvement of the signal-to-noise ratio. An improved signal-to-noise ratio can be accomplished via FM systems and may also Hearing assistive technology, in addition to targeted auditory training, other communicative environmental modifications, and compensatory strategies can vastly improve the day-to-day functioning of individuals with (C)APD. References: AAA (2003): Pediatric Amplification Protocol, October 2003. ANSI (American National Standards Institute) (2002). Acoustical performance criteria, design requirements, and guidelines for schools. ANSI S12.60. Melville, NY: Author. ASHA (2005a): American Speech Language Hearing Association (ASHA). (Central) Auditory Processing Disorders -The Role of the Audiologist. Technical report. ASHA (2005b): American Speech Language Hearing Association (ASHA). (Central) Auditory Processing Disorders. Technical report. Bamiou, D-E, Musiek, F.E. and Luxon, L.M. (2001): Aetiology and Clinical Presentations of auditory processing disorders - a review. Archives of the Disordered Child, 85, 361-365. Beck, D.L. Doty-Tomasula, M., and Sexton, J. (2006): FM Made Friendly. Bellis, T.J. (2002): When the brain can't hear: Unraveling the mystery of auditory processing disorder. . New York: Pocket Books. Bellis, T. J. (2003a). Assessment and management of central auditory processing disorders in the educational setting: From science to practice. Clifton Park, NY: Delmar Thomson Learning. Bellis, T. J. (2003b). Auditory processing disorders: It's not just kids who have them. The Hearing Journal, 56, 10-20. Bellis, T. J. (2006). Differential diagnosis of (central) auditory processing disorder in older listeners. In G.D. Chermak & F. E. Musiek (Eds.), Handbook of (central) auditory processing disorder, Volume 1: Auditory neuroscience and diagnosis. San Diego, CA: Plural Publishing. Chermak, G. D., & Musiek, F. E. (Eds.) (2006a). Handbook of (central) auditory processing disorder. Volume I: Auditory neuroscience and diagnosis.. San Diego, CA: Plural Publishing. Chermak, G. D., & Musiek, F. E. (Eds.) (2006b). Handbook of (central) auditory processing disorder. Volume II: Comprehensive intervention. San Diego, CA: Plural Publishing. Crandell, C., & Smaldino, J. (2004). Classroom acoustics. Seminars in Hearing, 25, 189-200. Jerger. J. (2000): Diagnosing Auditory Processing Disorders. JAAA, Vol 11, Editorial; http://64.239.26.35/professional/jaaa/display.php?f=jaaa/11_9/editorial.pdf Jerger, J., & Musiek, F. (2000). Report of the consensus conference on the diagnosis of Jerger. J., Musiek, F. (2002): A Reply to "Clinical and Research Concerns Regarding Jerger and Musiek (2000) APD Recommendations. Audiology Today, Vol 14, No 4. Katz, J. and Wilde, L. (1994): Auditory Processing Disorders. In "Handbook of Clinical Audiology," 4th Edition. Williams and Wilkens, Baltimore. ISBN 0-683-04548-2. Pichora-Fuller, K., Singh, G. (2006): Effects of Age on Auditory and Cognitive Processing: Implications for Hearing Aid Fitting and Audiologic Rehabilitation. Trends in Amplification. Vol 10, No 1. Smaldino, J.J. and Crandell, C.C. (2000): Classroom Amplification Technology: Sweetow, R. H., & Henderson-Sabes, J. (2004). The case for LACE: Listening and auditory communication enhancement training. The Hearing Journal, 57, 32-38. Weihing, J. (2005): FM Systems as a Treatment for CAPD. Hearing Journal. Vol 58, No 10. October, Pathways, Page 74. |
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