Auditory processing disorder (APD) is a deficit in the perceptual processing of auditory information in the central nervous system. According to the 1996 ASHA technical report on APD, the disorder is characterized by poor performance in one or more basic auditory behaviors or skills, including sound localization and lateralization, auditory performance with competing or degraded acoustic signals, auditory discrimination, auditory pattern recognition, and temporal aspects of audition. APD can affect individuals of any age, from birth through elderly, and it has been associated with difficulties in a variety of communication and learning arenas. In fact, some estimates suggest that as many as half of all children identified with learning disabilities and up to 75% of elderly listeners may exhibit APD.
Yet, despite an extensive body of literature that dates back to the 1950s, the topic of APD continues to be shrouded in a veil of mystery and misconception. Controversy still rages over how to diagnose and treat the disorder, as well as the relationship between APD and learning, language, and related difficulties. In some circles, there is even a question as to whether APD exists as a viable diagnostic entity at all. This is likely due to the heterogeneity of different types of APD, which precludes demonstration of a direct one-to-one relationship between deficits in fundamental auditory skills and learning or related difficulties across large groups of subjects.
At the same time, awareness of APD is steadily increasing among the lay population and those in other disciplines, and audiologists and speech-language pathologists are being called upon more and more frequently to address the disorder in their practices. As a result, many clinicians are entering into the APD arena with little, if any, educational preparation, leading to further misdiagnoses and misconceptions about the disorder. Many clinicians are now providing APD diagnosis and treatment services, and it is essential that clinicians who provide APD diagnosis and treatment services do so accurately.
In response to this crisis, ASHA has recently convened a working group for the purpose of updating the 1996 technical report to reflect current conceptualizations of the disorder and its assessment, diagnosis, and treatment. It is hoped that this document will be made available for peer review later this year. However, clinicians hoping for simple answers and cookie-cutter style procedural guidelines will be sorely disappointed. In fact, as we learn more about auditory processing, it becomes increasingly clear that, as with any disorder that involves the complex brain, there will never be one simple solution to the APD puzzle. Nevertheless, there are some general principles that guide the working group's conceptualization of APD and the means of diagnosing and treating it.
First, it should be emphasized that diagnosis of APD falls under the scope of practice of the audiologist. In collaboration with the SLP, who has a different focus in conducting assessments, an effective functional treatment and management plan can be developed for children with APD who also exhibit speech and language concerns. Although one may find many speech and language, psychological, and educational tests that include the term "auditory processing" in their titles, these are not to be considered diagnostic tests for APD. Instead, only those tests that exercise sufficient acoustic control and have been shown to be sensitive to disorders of the central auditory nervous system-while, at the same time, minimizing higher-order confounds such as language, memory, cognition, and related factors-should be used for APD diagnosis. The test battery used to diagnose APD should include both speech and non-speech signals that assess various processes and levels within the auditory system, and may involve both behavioral and physiologic measures (see sidebar on page 23 for examples). Further, because APD is a heterogeneous disorder that impacts different people in different ways, the selection of diagnostic test battery components must be individualized and appropriate for the child or adult in question.
A second guiding principle is that interpretation of APD test results should never occur in a vacuum. That is, in order to differentially diagnose APD from other disorders that may have similar symptoms, it is necessary to examine performance in other sensory modalities and disciplines, as well as across a variety of auditory tests. It is not enough simply to compare an individual's performance on a given central auditory test against available normative data and determine whether the overall score is within normal limits or not, as many different types of disorders may affect performance on even the most controlled auditory measure. Instead, audiologists should look for inter- and intra-test patterns that support the presence of specific auditory deficits. For example, the finding of ear differences on behavioral tests, hemispheric differences on topographic physiologic tests, and inter-test and cross-disciplinary patterns that correlate to well-established neurophysiologic tenets provide evidence for a diagnosis of APD. On the other hand, poor or inconsistent performance across all test measures and the absence of neurophysiologically tenable patterns would more likely be reflective of a global or higher-order attention, cognitive, motivational, or related confound.
Therefore, to be fully competent in diagnosis of APD, audiologists must have a working knowledge of the underlying science-including general and auditory neuroscience, cognitive neuroscience, cognitive psychology, and neuropsychology. However, education and training in these areas typically does not occur in most university-based professional preparation programs at present. As a result, those audiologists desiring to engage in APD service provision may need to seek out additional educational opportunities and study the pertinent literature in other disciplines in order to provide optimal patient care in the area of APD.
Although the responsibility for APD diagnosis falls to the audiologist, the full understanding of the functional ramifications of an individual's APD and the development of a comprehensive management and treatment plan requires multidisciplinary cooperation. SLPs, psychologists, educators, and others collaborate in the overall assessment and intervention process. Just as the diagnostic test battery must be individualized, so must the management and treatment recommendations. A comprehensive intervention plan for APD should include three primary components:
environmental modifications designed to optimize the communication, learning, and listening environment and improve access to auditory information
compensatory strategies that strengthen higher-order cognitive, language, and related resources so that they may be recruited to assist with comprehension and retention of auditory information
direct remediation activities, usually in the form of auditory training, that target specific auditory skill areas found to be deficient
The specific recommendations made in each of these areas will differ depending upon the individual's unique pattern of symptoms and test findings. Once again, there are no simple, cookie-cutter intervention recommendations appropriate for all children or adults with APD. Instead, the development of an intervention plan requires accurate diagnosis of the auditory deficit(s), familiarity with the literature regarding auditory neuroplasticity, interdisciplinary collaboration, and an inherent appreciation and understanding of the functional difficulties exhibited by the individual child or adult in question.
Although there is much that is known about auditory processing and its disorders, much remains to be discovered. Recent advances in neuroimaging and topographical brain mapping are helping us to have a better understanding of how auditory information is processed in the brain, and these findings will have a significant impact on our ability to diagnose and treat APD more efficaciously.
Clinicians interested in providing APD services are encouraged to avail themselves of the literature and continuing education opportunities on the subject so that many of the misconceptions that fuel the continued controversies may be dispelled and the focus can shift to where it is needed most: accurate diagnosis and treatment of children and adults with APD.