A surge in APD diagnostics occurred a couple of decades later during the 1970's. At that time, individual behavioral tests were combined into batteries for the purpose of identifying auditory processing disorders, especially in school-age children. However, nearly all of the tests were validated on adults. These adults had lesions of the temporal lobe or corpus callosum, leading to speculation that children with similar presentation patterns and test results suffered from disruptions in similar regions of the brain. There were significant concerns, however, that the tests lacked validity when used to diagnose processing disorders in children with no known lesions.
Furthermore, in those early days, there were no specific remedies available to treat APD once the diagnosis had been made. Ultimately, few audiologists chose to engage in APD diagnostics and academic programs provided limited training in this area of clinical practice.
The 1990's brought us to a new watershed in APD diagnostics. With increasing technology and the tremendous insights brought about by the "Decade of the Brain," clinicians, researchers, parents and educators are again directing their attention to better understanding and treating APD. Children continue to perform poorly in school in spite of adequate hearing, resources, intelligence, and traditional therapies. As a result, APD has once again emerged as a potential explanation for the learning difficulties experienced by schoolchildren.
In addition, adults with sophisticated digital hearing aids are complaining that in spite of their ability to adequately detect the auditory signal, they cannot process it normally. Clinicians and researchers alike are beginning to consider that processing deficits within the listener may contribute significantly to overall dissatisfaction with hearing aids and other assistive listening devices.
As a result, the audiologist faces many challenges in the assessment of listeners across the lifespan for APD. Unfortunately, many of the important questions from the 1970's related to diagnostics and management of the disorder remain unanswered. Research efforts are underway to provide us with more assured standards for both diagnostics and remediation and in the meantime, there are several "best practice" methods that can be used.
The purpose of this article is to describe those methods as they relate to the diagnosis of one particular pattern of auditory processing deficits in both children and adults referred for testing.
Binaural integration performance has been the focus of a significant amount of attention over the past several decades. This task is assessed through a variety of dichotic listening tests with digits, words and consonant-vowels. Performance in each ear is measured as material is simultaneously presented in competition to the two ears. The presence of a large interaural asymmetry has been a hallmark of a processing disorder, usually described as a left-ear deficit.
Many audiologists report that a majority of the individuals seen by them for APD fit an Integration Deficit profile, characterized primarily by a large interaural asymmetry during dichotic speech tests. A number of studies have identified the presence of binaural integration deficits in children with learning and reading disorders (Hynd, et al., 1979; Obrzut, et al., 1988; Moncrieff & Musiek, 2002). Interestingly, a similar pattern has been recognized in adults who demonstrate difficulty wearing two hearing aids (Jerger, et al., 1993). For many years, dichotic listening tests have been an essential part of the test battery for assessing individuals of all ages (Jerger & Musiek, 2000).
Two readily available tests that include dichotic listening components are the SCAN-C (Keith, 2000) and the Staggered Spondaic Word Test (SSW, by Katz, 1963). Both have normative data for adults and for children, as young as age 5. Many children can perform the tests with sufficient skill that auditory processing deficits can be readily revealed. Audiologists have relied on one or both of these tests for many years, but a note of caution is needed when using these tests.
The SSW includes some word pairs that are essentially out of date. For example, "band saw" and "soap flakes" are no longer familiar terms to most of today's children. The test has been made available on a compact disc, but the recording has not been updated or improved, leaving a significant amount of background noise on the test. For some children, the noise can be distracting, especially if a presentation level at a higher intensity level is needed.
Normative data was collected on the SCAN-C in 2000 and the test was re-issued on a compact disc. Many children reportedly achieve normal standard scores on subtests of the SCAN-C, although their parents and teachers note significant difficulty at home and in the classroom with auditory performance. Audiologists are encouraged to read the instruction manual carefully and while scoring the test, be sure to include typicality measures for the Competing Words subtest. When the scores for the two ears are combined on that particular test, much of the important information about interaural asymmetry can be lost. A standard score may reflect normal performance, even when the left ear is performing very poorly. Because a left-ear deficit is a significant indicator of a binaural integration deficit in auditory processing, it is essential that each listener's performance on the Competing Words subtest be evaluated for an interaural asymmetry.
To determine interaural differences, Keith recommends that typicality measures be calculated for each of the two listening conditions, right ear first and left ear first. When results indicate atypical performance in either or both conditions, he instructs that the listener be further evaluated with additional dichotic listening measures.
One potential problem with the typicality measures is that they are determined separately for each of the two listening conditions. Hypothetically, a child might be very good at directing attention during the test and perform with a large right-ear advantage in the right ear first condition and then perform with a left-ear advantage in the left ear first condition. This could potentially produce atypical results by Keith's measures. Under some circumstances, a different comparison of the total score for the right ear and the left ear across both listening conditions may ultimately produce a very small difference between the two ears.
To illustrate this point, here are hypothetical SCAN-C results for a 9 year old child:
Typicality measures are based on raw score differences between the two ears in each listening condition and can be influenced by the child's ability to focus his attention effectively. In some instances, they may reflect unusual performance in a given child. When the total score is combined for each ear and converted to a percent correct, the overall ear advantage calculated as a simple percent difference across the entire test may actually be at a fairly normal level. For this reason, it is recommended that a simple difference between the two ears be calculated for the Competing Words subtest. Then, if results are both atypical and reflective of a significant interaural asymmetry across the entire test, the performance should be cross-checked with at least one other dichotic listening test.
The Dichotic Digits Test is a powerful tool for diagnosing binaural integration problems and is an especially good test for use with children. Normative data on one double digits version (Musiek, 1983) is available for children as young as age 7. One potential weakness, however, is that the double digits test may result in ceiling effects when used with older children (age 10 and older) (Moncrieff & Musiek, 2002). As a result, the clinician may need to increase the demands of the task by using triple digit pairs rather than doubles. Unfortunately, no normative information is currently available for triple digits in children, but the presence of a significant interaural asymmetry observed with a triple digits test could help support the diagnosis of APD in an older child. Efforts are underway to update behavioral tests and develop new tests that will be useful in this important diagnostic battery. A Randomized Dichotic Digits Test has been created for which normative information is available for adults (Strouse & Wilson, 1999a, 1999b). This same test may also prove helpful in pediatric diagnostics.
In spite of the large number of individuals identified with binaural integration deficits, there is no specific treatment available for its remediation. Some argue that with children, poor left ear performance is only a matter of maturation and that younger children will outgrow the deficit. There is a significant amount of evidence to the contrary, however, in the large number of older children and adults with integration deficits that have been resistant to traditional remediation efforts (Cacace & McFarland, 1998; Moncrieff, Lombardino, LeGrand, Chitty & Peacock, 2002). Children continue to demonstrate significant interaural asymmetries on dichotic listening tests following treatment with commercially available programs such as FastForWord and Earobics (Wertz & Hall, 2002), suggesting that this particular deficit may need a different kind of therapy.
A pilot study was done in the Auditory Processing Laboratory at UF this summer (2002) to investigate the efficacy of a new technique directed toward improving binaural integration ability. It is hoped that these types of research efforts will ultimately lead to techniques that improve outcomes with individuals who suffer from this processing deficit.
In the meantime, audiologists can facilitate these efforts by identifying the deficits in the listeners they see. Three primary profiles that are currently being identified are the Auditory Decoding Deficit, the Integration Deficit and the Prosodic Deficit (Bellis & Ferre, 1999). Each is identified through a pattern of deficits on a variety of auditory processing tests and each includes a specific pattern of results on binaural integration tasks. The clinician can best provide information on the overall prevalence of APD and on the relative prevalence of each profile within the diagnosis. Combined with the groundswell of interest that has recently emerged among families, educators, co-workers and friends of individuals with processing problems, this information can help support a variety of initiatives in this important area of research. As improvements are made in the identification of specific deficits, researchers can work toward developing remediation techniques that are precisely targeted toward those weaknesses.
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