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What is it about hearing that enables us to determine if the lyrics to a Creedence Clearwater Revival song are: "There's a bad moon on the rise" or "There's a bathroom on the right"? How is it possible to have a conversation on a cell phone while riding the noisy MARTA train in downtown Atlanta? How can someone know from which direction a speeding car is approaching in the midst of traffic noise? How can we tell if someone is being serious or just joking when they maintain a straight face? All of these scenarios demonstrate that hearing is not just about soft or loud sounds. It is auditory processing within the brain that makes it possible for us to make sense of the world of sound in which we live - and for children, who are trying to figure out everything all at once, auditory processing is especially important.
Auditory processing has been defined loosely as "what we do with what we hear." Intuitively, hearing involves input to the brain, but the brain must then take what it hears and process it into meaningful units of information. Given the many different ways in which auditory behaviors can be observed, it often helps to think of auditory processing as a set of abilities or skills that are rooted in the neurobiology of the brain. Some of the "real-life" abilities or skills include: knowing from which direction a sound is coming (localization); telling the difference between two keys on a piano (discrimination); following a melody (ordering); understanding someone in a noisy restaurant (competing sounds); or even understanding someone who does not speak clearly (degraded sounds). None of these skills take place in isolation. A deficiency in one or more of the auditory processing abilities or skills mentioned above might indicate an auditory processing disorder (APD). Also, auditory processing is influenced by other higher-order processes in the brain including language, attention and memory.
When language, attention and memory are typical, a deficiency in one or more auditory processing skills might indicate an auditory processing disorder. Diagnosing APD is difficult, however, when a child may also have a language, learning or attention disorder. It is not easy to differentiate among these disorders, particularly when they may share many of the same behavioral symptoms that affect the ability to listen to or comprehend speech.
Unfortunately, APD is highly variable and diverse from person to person and there simply is not a one-size-fits-all approach to diagnosis, management or treatment. In other words, there is a continuum of APDs, where different profiles, or categories, of the disorder can be expected. Because the reasons for APD can vary so widely, recent discussions among experts in audiology suggest that a multidisciplinary approach is necessary for diagnosing APD. An audiologist may be the one to conduct a comprehensive hearing evaluation, complete with a battery of auditory processing tests aimed at revealing auditory processing deficits; however, the audiologist will only make the diagnosis of APD on the basis of related information from other professionals. School and clinical psychologists would be able to provide information about cognitive, attention and social interactions, as well as measures of verbal and nonverbal intelligence. Teachers and parents could provide information about academic performance and general auditory/listening skills at home and school. A physician would be able to determine if there might be any underlying medical or anatomical concerns that might lead to symptoms of deficient auditory processing. A school speech-language pathologist would be able to rule out a language or learning problem, or infer that auditory deficits are leading to the language or learning deficit. In many cases, it will be the school speech-language pathologist who administers auditory training for APD or auditory-based training to try to improve other weak language or learning areas.
Before any child is tested for APD, some experts recommend screening for APD. Whereas there is no universally accepted screening method, a variety of published and commercialized tools does exist. And screening for APD does not have to be conducted by an audiologist. Some tools that have become available recently include the Differential Screening Test for Processing (DSTP) and Auditory Processing Abilities Test (APAT). These tools, along with recommendations of a multidisciplinary team, may determine whether comprehensive testing is needed or not.
When warranted, comprehensive testing includes a battery of tests. Most clinics use behavioral tests, in which the child listens to certain sounds and then performs a task in response to the sounds. For example, there are dichotic listening tests, in which the child may hear one or more words in each ear, but the words presented to both ears are different. Either the child is asked to name every word regardless of which ear heard the words, or he must attend to one ear and ignore the other and name only the words in the attended ear. Some tests involve speech sounds or sentences that have been filtered or presented in a background of noise. Another group of tests examines how well the child can organize simple tones either by pitch or by how long or short the tones are. Still other tests provide insight into a child's ability to put individual speech sounds into complete words and reveal the duration of a child's attention span while performing an auditory task. For most tests, the child must be at least seven or eight years old. This is because typically-developing children vary so much in their verbal and motor skills below age seven. Thus, many tests simply lack normative data for children below age seven. Another critical issue is whether or not younger children can understand the instructions and perform the tasks necessary to obtain reliable results. Finally, there are also the issues of the child's attention, motivation and energy levels.
In the last few years, several clinics around the country have considered adding auditory evoked potential (AEP) test measures to their APD test battery. AEP tests provide information about how the auditory nervous system is functioning through the analysis of recorded brainwaves. Electrodes are placed on the skin surface of the child's head and ears and the child will nap, sit quietly, watch a movie or perform a task. The recorded brainwaves then can be compared to the brainwaves of other children in the same age range, or they may be compared for differences between ears or hemispheres of the brain. Any differences found may support the findings of the behavioral tests or may identify subtle abnormalities not found in behavioral tests. If APD is diagnosed and an auditory training program is implemented, the brainwaves may be recorded later to determine if there were improvements.
If APD is diagnosed, the multidisciplinary team determines how to treat and manage the disorder. While there are many approaches to helping children with auditory processing diffi culties, it should not be assumed that all approaches will work for every child. There are three generally accepted approaches that may be implemented alone or in combination with one another: environmental modifications, compensatory strategies and auditory training.
Environmental modifications generally involve making a change within the educational setting to improve access to sound. Many classrooms are noisy simply because they are full of active children whose voices bounce off linoleum floors and concrete walls. In order for a child to understand the teacher (or other students in the classroom), he needs to be able to hear the teacher's voice at a louder level than the surrounding background noise. This could be accomplished by reducing noise, making the teacher's voice louder or a combination of both. Simply adding carpeting and drapery to a classroom can go a long way in helping to reduce noise because the soft material will absorb sound rather than reflect it. There is only so much that can be done about noise, though, which is why it is also a good idea to enhance the teacher's voice using an amplification system involving a microphone and speakers. Commonly referred to as a soundfield system, this modification benefits everyone in the class. In fact, research has indicated that amplification in the classroom is helpful for children even up to 15 years of age. When it is cost-prohibitive to provide a soundfield system in every classroom, a personal amplification system (assistive listening device) that the child can take from class to class is also helpful. The teacher still wears a microphone but the enhanced sound is delivered directly to the ears of the student with APD, using a personal device. Recently, researchers found that ear-level assistive listening devices were beneficial to children with APD. A hearing healthcare professional can be consulted for recommendations about a soundfield or personal device.
Compensatory strategies generally involve helping the child cope with APD by enhancing other cognitive skills, such as language and social skills. For example, children with APD could be taught to use their language skills to fill in the blanks when they hear partial or degraded speech. Compensatory strategies that work are bound to help improve auditory behaviors even when the auditory system, or auditory processes themselves, have not improved.
Finally, auditory training generally involves informal and formal methods that aim to positively influence the structure and function of certain auditory processes within the brain. Indeed, the brain is constantly developing and changing (a process known as "plasticity"), and the child with APD might benefit from some type of auditory training. Some informal methods that most children could benefit from include playing games like Marco Polo, MadGab, Simon or Bop It; playing rhyming games or listening-in-noise games and musical chairs; tackling verbal math problems; reciting phone numbers; and finding key words to a spoken passage or story.
In summary, APD encompasses one or more auditory processing abilities or skills. However, because APD is often difficult to differentiate from language disorders, learning disorders and attention
disorders, diagnosis requires a multidisciplinary approach. When a diagnosis of APD is made, the multidisciplinary team should develop an intervention strategy specific to the auditory processing
deficit, being aware that not all intervention approaches will help all children with APD, and keeping in mind that the strategy must be dynamic to meet the child's needs.
Samuel R. Atcherson, Ph.D., is an assistant professor of audiology and clinical director of audiology with a joint faculty appointment in the Department of Audiology and Speech Pathology at the University of Arkansas at Little Rock and the University of Arkansas for Medical Sciences. Contact him at SRAtcherson@ualr.edu.
