Central Auditory Processing Disorder: When is Evaluation Referral Indicated?
By: Sandra Cleveland
The comorbidity of central auditory processing disorders with attention deficit disorders has been well documented. But often a child's initial diagnosis depends largely on whether he or she is seen by an audiologist or psychologist. Therefore, it is important that professionals be aware of when an auditory attention deficit and central auditory processing disorder may cormorbidly exist in order to make appropriate referrals for further evaluation.
It is often suggested that a child with an attention deficit be referred for an auditory processing evaluation when school performance is poor or when tasks that require listening skills are problematic.
This certainly would appear instructive when evaluating an older child. However, in younger children the manifestation of symptoms may be subtle and not apparent when evaluating academic functioning. Subsequently, referral for an auditory processing evaluation may be delayed. Therefore, it is important to recognize additional factors that may flag the need for referral to an audiologist.
The American Speech-Language-Hearing Association (ASHA) Task Force on Central Auditory Processing Consensus Development has defined auditory processing disorder as "a deficiency in one or more of the following phenomena: sound localization and lateralization, auditory discrimination, auditory pattern recognition, recognition of temporal aspects of audition, auditory performance decrease with competing acoustic signals, and auditory performance decrease with degraded signals." They further indicate that auditory processing disorders may stem from, or coexist with attentional deficit disorders.
The prerequisites for auditory processing are as follows: auditory attention, auditory memory, motivation, maturation and integrity of the auditory pathways, decision processes, and use of linguistic cues such as grammar, meaning in context, and lexical representations. All auditory tasks are influenced by these factors. Difficulties in many of these areas are common to both children with central auditory processing difficulties and children diagnosed with attention deficit disorders , and it has been reported that both groups can show difficulties paying attention, following directions, are hyperactive, distracted, and can become easily frustrated. Organizing and sequencing information presented via the auditory track is also problematic. These characteristics can also be seen in children with learning disabilities, behavioral problems, or emotional disorders. Separating the above groups requires cooperation among professionals in order for the appropriate remedial plans to be devised.
In addition to poor academic functioning, the following risk factors or indicators may assist the professional in making a referral for an auditory processing evaluation in a timely manner.
A family history of auditory processing difficulties can be an indicator for referral. It is not uncommon to find that children with auditory processing difficulties have a family member who has had similar difficulties.
A second genetic influence that should prompt a referral to an audiologist is a family history of peripheral hearing loss. Peripheral hearing loss must be ruled out or confirmed prior to a diagnosis of attention deficit or central auditory processing disorder. Not only is early identification of a hearing loss critical, but children or adults with hearing loss certainly have greater than normal difficulty attending to auditorily presented information. What might appear as a processing problem or attentional deficit may reflect the reduction or distortion of auditory signals. However, the presence of a peripheral hearing loss does not exclude the possibility that the individual also has an attentional deficit or auditory processing problem.
A history of otitis media in early childhood is another factor that may indicate the need for an auditory processing evaluation, as otitis media can have an adverse effect on the development of auditory processing abilities . The age of onset, number of episodes, and duration, are important factors. Hohn and Kunze found that auditory skills were significantly depressed in those children with a significant history of otitis media in early life. Visual skills and other cognitive tasks were not significantly different between the two groups. Research using a prospective study design was completed by Schilder and colleagues. They found that children with a history of persistent otitis media at a preschool age showed only slight effects on their ability to discriminate speech in noise. However, the subjects in this study received ventilation tubes on a routine basis if the episode of otitis media persisted for more than 2-3 months. This illustrates the effects of duration of the otitis media episode on the development of auditory processing skills.
Familial handedness is another factor which should be explored. Not only has it been found that an individual's hand preference is a diagnostic indicator, but also that a familial history of handedness can help to predict brain organization for language processing.
A hypersensitivity to loud sound or distractibility in noise may be additional indicators for referral. It has long been assumed that children with auditory processing disorders have a lower tolerance for loud sounds due to abnormal central suppression effects. Likewise, Geffner, Lucker, and Koch found that children with attention deficit disorder had significant differences (from normal controls) in their preferences for comfortable listening levels and tolerance of loud sounds. This raises the question of whether children with attentional disorders have deficits in central suppression that need to be evaluated for appropriate management in the classroom.
A child presenting with developmental speech and language delays, including articulation problems, can also be at risk for central auditory processing problems. Even a past history of speech and language delay may place the child at risk for associated central auditory processing difficulties and a referral may be indicated. Children having delays in these areas generally have poor phonic ability and subsequent difficulties in reading and spelling. Central auditory processing tasks involving blending, closure, and sequencing can be an area of weakness in these children.
The purpose of the central auditory processing evaluation is to help define the specific auditory processing difficulties that a child may be experiencing and to recommend appropriate remediation. Performance on auditory processing tests is measured according to chronological age expectancies. It is generally believed that development of the auditory processing pathways continues up to age 12 or 13. The premise of testing is that degraded speech, or speech in noise, will tax the auditory pathways of the central nervous system more than recognition of unaltered speech or speech in quiet. An individual with normal central auditory processing abilities can, to some extent, compensate for these degraded signals, whereas an individual with a central auditory processing deficit cannot.
Early work on central auditory processing was completed on brain-lesioned adults. Words were filtered in order to reduce intelligibility. Results of Bocca and colleague's research indicated that discrimination was poorer in the ear opposite the side of the lesion. Research evaluating the effects of manipulation of the speech or tonal signals on auditory perception continues to date. For an extensive review of the major developments that have occurred in the area of central auditory processing, the reader is referred to an article by Musiek and Baron.
Behavioral measures presently used include the various manipulations of speech and non-speech signals such that they are frequency-distorted, compressed in time, or are administered in the presence of a competing signal (e.g., noise). Materials are also presented in a dichotic mode such that different signals are presented to each ear simultaneously, requiring the individual to either separate or synthesize the information. Ideally, an auditory processing test battery will include a variety of measures that correlate with different central auditory processing skills and behaviors in the classroom.
Temporal processes have been found to correlate with spelling and reading skills. The temporal processes are evaluated using tests that require the individual to perceive patterns (e.g., tonal patterns) and to then verbalize the sequence (e.g., High-High-Low). The premise of temporal processing tests is that an interaction between both hemispheres of the brain is needed in order to decode patterns and report them verbally.
Low-redundancy speech materials assess the processing of speech that has been filtered or is masked by a competing signal such as noise. These materials have been altered so that the extrinsic cues in the signal have been reduced. The individual then needs to rely on the intrinsic cues provided by their auditory systems to perceive the signal. If intrinsic redundancy is compromised, performance will be adversely affected. Performance on these tests frequently correlate with speech discrimination ability in a classroom where background noise is present or where reverberation of the sound source is causing distortion of the primary signal.
The interaction between the right and left hemispheres, and subsequently maturation of the auditory system, is evaluated using dichotic tasks. These materials present different stimuli to each ear simultaneously and require the listener to repeat the two signals heard. Prior to complete maturation of the auditory system or, in cases of dysfunction, sounds heard in the less dominant ear (generally left ear) are "beaten out" by signals presented to the more dominant ear. Research evaluating performance on dichotic tasks has shown promise in assisting the professional in making a differential diagnosis between children with attention deficit and auditory processing disorders and those with only attention deficit or auditory processing disorders.
Binaural interaction tasks evaluate the ability of the brainstem to synthesize partial auditory information presented to each ear into a complete intelligible message. Children having difficulties on these tasks are often found to have difficulty listening in the presence of background noise.
Phonemic synthesis and sound blending are other skills evaluated. Difficulties in these areas frequently can be seen in children having reading, spelling, and language problems.
Physiologic measures include evoked potentials testing and otoacoustic emissions evaluation. Research utilizing these measures and associating results with their behavioral correlates is in its infancy. These measures assess electrophysiologic measures of the auditory system relating to such phenomena as attention, detection of signals in noise, and perception of signals.
Management techniques are generally classified into two categories: enhancement of the primary signal via manipulation of the listening environment, and specific training of auditory skills. The latter will frequently include the teaching of compensatory strategies that allow the child to better function in the classroom and at home. The below discussion mentions only a few of the many recommendations that may be made for a child with an auditory processing disorder.
The presence of background noise or acoustic reverberation of the speech signal can significantly compromise the child's ability to receive the desired speech signals. Reduction of noise in the classroom can be accomplished by acoustic treatment of the room by use of acoustic tiling, draperies, or carpets. Reverberation of speech will likewise be reduced with such modifications. Further, teachers should be aware that when he or she speaks toward a reverberant surface such as the chalkboard, the speech signals will most likely be distorted. A visual display of information presented auditorily can be useful. In addition to the above suggestions aimed at improving the signal quality, the primary signal can be enhanced by increasing the volume of the desired signal. This can be accomplished via the use of preferential seating toward the primary speaker, or by use of an amplification device such as a wireless F.M. system, a device worn by both the child and by the primary speaker. The child wears a headset and receiver which is coupled similar to a personal stereo. The speaker uses a lapel-worn microphone. Use of this F.M. system helps to maximize the level of the teacher's voice, and background noise and poor acoustics are minimized since the child receives the teacher's voice as if in a one-to-one listening situation. Fitting of such a system needs to be completed by an audiologist in order to minimize any adverse effects.
Specific training of auditory skills and compensatory strategies is generally provided by a speech and language pathologist. Young children diagnosed as having auditory processing disorders should be seen by a speech and language pathologist in order to determine if subtle language deficits are impacting on their ability to process speech. Emphasis of training can revolve around increasing knowledge of phonology, grammar, vocabulary, and world knowledge in order to help the child "fill in the blanks" of a message that may be unclear.
Auditory processing disorders comorbidly exist with attention deficit disorders. Our means of identifying this coexistence is many times more an art than a science. Research continues to assist in the differential diagnosis of these two disorders. Until further indicators are developed, awareness on the part of the professional may help in the identification process.
About the author
Sandra Cleveland has a Master's degree in Audiology from Northeastern University. She has primarily worked in pediatric settings, including Children's Hospital, Boston, Mass. Presently, she is the Director of Audiology Clinical Services at Northeastern University
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Sandra Cleveland, M.S. The ADHD Report Volume Five, Number 5, October 1997