Central auditory processing disorders in children and adults

Abstract

Central auditory processing disorders (CAPD) can affect children and adults of all ages due to a wide variety of causes. CAPD is a neurobiologic deficit in the central auditory nervous system (CANS) that affects those mechanisms that underlie fundamental auditory perception, including localization and lateralization; discrimination of speech and non-speech sounds; auditory pattern recognition; temporal aspects of audition, including integration, resolution, ordering, and masking; and auditory performance with competing and/or degraded acoustic signals (American Speech-Language-Hearing Association, 2005a, American Speech-Language-Hearing Association, 2005b). Although it is recognized that central auditory dysfunction may coexist with other disorders, CAPD is conceptualized as a sensory-based auditory disorder. Administration of behavioral and/or electrophysiologic audiologic tests that have been shown to be sensitive and specific to dysfunction of the CANS is critical for a proper diagnosis of CAPD, in addition to assessments and collaboration with a multidisciplinary team. Intervention recommendations for CAPD diagnosis are based on the demonstrated auditory processing deficits and related listening and related complaints. This chapter provides an overview of current definitions and conceptualizations, methods of diagnosis of, and intervention for, CAPD. The chapter culminates with a case study illustrating pre- and posttreatment behavioral and electrophysiologic diagnostic findings.

Introduction

Central auditory processing disorders (CAPD) can affect children and adults of all ages. Etiologies ranging from trauma to neurotoxic substances and neurologic disease or insult may cause dysfunction in the central auditory nervous system (CANS), resulting in a CAPD (American Academy of Audiology, 2010). In addition, CAPD may coexist with and/or mimic other disorders that affect listening, learning, and communication, particularly in children. Musiek et al. (1985; Musiek and Gollegly, 1988) postulated three primary underlying etiologies of CAPD in children: (1) neuromorphologic disorders, including atypical left/right anatomic asymmetries in planum temporale, ectopic areas, and polymicrogyri (65–70%); (2) neuromaturational delay (25–30%); and (3) neurologic disorder, disease, or insult (< 5%). Although frank neuropathology may be relatively rare in children, the effects of acquired neurologic disorders on central auditory function in this population have nonetheless garnered recent attention (Chermak and Musiek, 2011). Similarly, in recent years, evidence of atypical neuromorphology in children with CAPD has been presented (e.g., Boscariol et al., 2009, Boscariol et al., 2010, Boscariol et al., 2011; Fig. 30.1). It has been estimated that CAPD affects 2–5% of the school-aged population, or approximately half of all children with learning disorders, and up to 76% of elderly adults, depending on the criteria used for diagnosis (Cooper and Gates, 1991, Chermak and Musiek, 1997, Bamiou et al., 2001, Golding et al., 2004).

More recently, increasing attention has been focused on the prevalence of CAPD in adults with acquired traumatic injuries, including returning war veterans and individuals involved in contact sports (e.g., Okie, 2005, Martin et al., 2008, Malloy and Bellis, 2013). In a recent study by Gallun et al. (2012), behavioral and electrophysiologic tests were administered to 36 blast-exposed veterans and 29 controls. Results indicated that the blast-exposed veterans exhibited a threefold increase in abnormalities on tests of central auditory function and speech in noise, despite normal peripheral hearing sensitivity. Similarly, Malloy and Bellis (2013) studied eight Division 1 football players with no history of diagnosed concussion. When compared to age- and education-matched controls with no history of participation in contact sports at the high-school level or above, the football players exhibited significantly smaller amplitudes and longer response latencies on several auditory evoked potential measures. These results indicated that the types of recurrent impulses and impacts experienced by those involved in contact sports such as football may result in central auditory deficits.

In short, CAPD is a distinct clinical disorder that has gained increasing attention in the literature over the past two decades. This chapter will provide an overview of current definitions and conceptualizations, methods of diagnosis of, and intervention for, CAPD. The chapter will culminate with a case study illustrating pre- and posttreatment behavioral and electrophysiologic diagnostic findings.