With an increasing number of children being referred for suspected auditory processing disorders (APD), audiologists continue to look for improved methods of screening and diagnosis. Although the incidence of children with APD has been estimated to be 2 percent to 3 percent¹, the rising referral rate has been attributed to the fact that there are a number of coexisting childhood disorders characterized by similar behaviors.

For the audiologist, this poses a diagnostic challenge-and a referral opportunity. The challenge audiologists face is that of differentiating APD from other disorders and making appropriate recommendations to reduce the detrimental effects of APD on the child. Because APD has been associated with a number of childhood disorders requiring a team approach to treatment, audiologists now have an opportunity to work more closely with other child specialists and develop a wider referral base.

Traditionally, audiologists primarily have been involved with diagnosis and recommendations regarding classroom acoustics. Therapeutic management primarily has been delegated to speech-language pathologists. In recent years, however, audiologists have acquired better diagnostic tools to use in assessment and have begun to explore ways of remediating APD. As evidenced by several presentations at the 2001 American Academy of Audiology Convention, an increasing number of innovative techniques and computer-assisted approaches are being applied to this population.

Audiologists use a variety of tests to assess APD in children. Since there has been no consensus on which tests to employ in particular circumstances, the choice of tests used often depends upon the background and experience of the audiologist. While graduate programs may offer coursework in auditory processing, many audiologists have acquired their knowledge of APD through continuing education because of their interest in and involvement with the pediatric population referred for such testing. As a result, there is considerable diversity from one setting to another in the number and type of auditory processing tests administered.

The need for some type of standardization or consensus has long been recognized. In an effort to clarify the issues regarding APD, several auditory scientists and audiologists convened in April of 2000 at the Bruton Consensus Conference, held at the Callier Center for Communication Disorders at the University of Texas at Dallas, to propose new guidelines for screening, differential diagnosis and a minimal test battery.²

Recognizing that disorders in processing may include both peripheral and central sites, the term central auditory processing disorder has been replaced with APD, which is broadly defined as a deficit in the auditory modality, characterized by problems with listening, understanding speech, language development and learning.

Diagnosis
Diagnosis of APD may be complicated by several factors. The heterogeneous population may have coexisting childhood disorders such as attention deficit hyperactivity disorder (ADHD), language impairment, learning disability or cognitive impairments. Many of the APD assessment procedures now used may fail to differentiate APD from other problems, resulting in a possible misdiagnosis. Furthermore, interpretation of tests may be confounded by a patient's lack of motivation, difficulty with sustained attention, or inability to cooperate. As a result, screening checklists and tests may offer ways of determining which children are appropriate candidates for comprehensive testing.

Many checklists currently use reference behaviors that are influenced by nonauditory factors such as language, memory and attention. An appropriate auditory-specific checklist would include items such as difficulty understanding in the presence of background noise, difficulty understanding rapid or indistinct speech, problems following oral instructions in the absence of language impairment, difficulty with discrimination, and problems with auditory attention. Such checklists need to have a clearly defined pass/refer criteria. The few screening tests that are available use linguistic stimuli and are time-consuming.

Effective Tests
An effective screening test should be brief and include a free-recall dichotic digits test and a gap-detection test. Because children under 6 years may not be able to participate in screening tests, checklists may be the most appropriate tool to use.

Differential diagnosis of APD from the other childhood disorders that often are comorbid and characterized by similar behavioral problems is necessary.

Factors that can impact a child's test performance include stress, medication, cognitive level and language ability. Because of this, effective APD tests should minimize linguistic variables and have limited cognitive and memory requirements. Responses to test stimuli should be simple, especially when a child exhibits oral-motor and/or sensorimotor difficulties. Pediatric APD testing may require more than one test visit, as familiarity with the examiner and reduced anxiety may improve reliable test performance. Even observation of the child during preliminary audiometric testing may help in determining if the child has the vigilance and linguistic ability to be reliably assessed.

The Bruton Conference proposed a minimal, auditory-specific test battery that uses both behavioral and electrophysiological measurements. In addition to pure tone audiometry, tympanometry and reflex testing, it was recommended that performance-intensity function, a dichotic test (digits, words, or sentences), a test of temporal processing (duration pattern sequencing), a gap detection test, otoacoustice emissions (OAE), auditory brainstem response (ABR), and middle latency response (MLR) be administered.

While this proposed auditory-specific battery lacks the ability to differentiate APD from other disorders, it will identify specific deficits within the auditory system. Working with educational psychologists, speech-language pathologists and child study teams can help in the diagnostic process and establish the audiologist as a member of the team.

Since there is a relationship between APD and dyslexia, audiologists also may want to establish relationships with reading specialists, further expanding their referral base.

Audiologists traditionally have made recommendations focused on preferential seating, reduction of ambient noise, and use of assistive listening devices (ALD) in attempts to minimize the effect of ambient noise on spoken language recognition. Studies show classrooms often exhibit signal-to-noise ratios that are known to degrade speech recognition.

Contributing Factors
While ambient noise has been recognized as contributing to APD, less attention has been given to the effects of classroom reverberation. Large classrooms, classrooms that are irregularly shaped, and classrooms with minimal sound-absorbing materials pose problems for the child with APD. Because the synergistic effect of noise and reverberation contribute to greater speech perception problems than either one by itself, audiologists need to make educators aware of both when making recommendations. Otherwise, a recommendation of preferential seating, which may not ensure an appropriate listening environment, may be misconstrued as sufficient accommodation. This has led to an increasing interest in the benefits of sound field FM amplification in the classroom.

Computer Assistance
With the knowledge that neuroplastic changes can occur in the central auditory system, audiologists have begun to explore the possibility of improving APD.

One such approach is Fast ForWord,³ a program that uses a combination of sweep frequency and algorithmically altered phonemic and linguistic stimuli that are developmentally appropriate for the pediatric population diagnosed with APD.

Fast ForWord training adapts progressively to the individual child's processing ability to drive changes in the auditory nervous system. Several studies have indicated improvement in APD following Fast ForWord training, including children with cochlear implants, APD, and abnormal MLRs.^4-6 Functional magnetic resonance imaging (fMRI) of dyslexic adults with left temporal involvement also has been shown to improve following the use of Fast ForWord.⁷

Technological advancements in synthesized speech and the capability of computers to provide consistent stimuli in a repetitive manner have greatly increased the possibilities of improving APD.

Research Needed
Referrals of school-aged children are increasing, and additional research is needed to provide more appropriate APD screenings and tests.

At the same time, as the field of audiology moves to a doctoral-level profession, the need to include coursework on APD is becoming apparent. Several AuD programs, such as the one offered by Central Michigan University, in Mount Pleasant, MI, now include such curriculum.

As audiologists enter the new millennium, the need to keep up with changes in pediatric diagnostics and management is apparent, particularly in the area of APD, as we seek to improve our service to children with auditory impairments.

References

1. Chermak, G., Musiek, F. (1997). Central Auditory Processing Disorders: New Perspectives. San Diego: Singular Publishing.

2. Jerger, J., Musiek, F. (2000). Report on the consensus conference on the diagnosis of APD in school-aged children. Journal of the American Academy of Audiology, 11 (9):467-474.

3. Tallal, P. et al. (1996). Temporal processing deficits of language-learning impaired children ameliorated by training. Science, 271.

4. Schopmeyer, B., et al. (2000). Annals of Otorhinolarygology (Suppl. 185), 109 (12), Part II.

5. Battin, R., Young, M., Burns, M. (2000). Use of FastForword in remediation of CAPD. Audiology Today, March: 13-15.

6. Berlin, C. (2001). Fast ForWord for some children with auditory deprivation. Presentation at the American Academy of Audiology, San Diego, CA.

7. Temple, E., et al. (2000) Disruption of the neural response to rapid acoustic stimuli in dyslexia: Evidence from functional fMRI. PNAS, 97.

Maxine Young is in private practice in Broomall, PA. She can be reached at (610) 353-6008 or via e-mail at maxyoung@sprynet.com.