Auditory Processing has been defined by CAPD pioneer, Dr. Jack Katz, as “What we do with what we hear.” An analogy I like to use with my patients is that of a sound system. The ears, and their peripheral function, can be compared with a microphone (a transducer which converts sound waves in the air into an electrical signal). A microphone is an important component in high-fidelity sound reproduction. But unless the microphone is plugged into a quality processor, its information is either distorted or lost.
Our ears–when in healthy, undamaged condition–are like precision microphones–amazing, high-quality transducers of sound. But in order for them to work as intended, they depend on the incredible processing of the central auditory nervous system (CANS) to receive their signals and convert them into meaningful, intelligible, and faithful reproductions of the sounds entering the ears. In effect, we ultimately “hear” with our brain, not our ears. In the same way, we “see” with our brain, not our eyes, which are incredible biological cameras. Damage to the transducers (microphones or cameras) will limit the processor’s ability to faithfully reproduce the input signals as high-definition hearing or vision. Damage to the processor will result in distorted, reduced-fidelity reproduction of inputs, no matter how intact they were leaving the transducer–in our case, the ear.
People whose conventional hearing evaluation indicates normal peripheral hearing at the ear-level have good “microphones.” If they fail to experience quality sound perception–poor word recognition, difficulty extracting speech from degraded conditions (noise, poor acoustics, diminished-quality speech inputs), then the likely culprit is at the CANS level–the brain-stem or higher brain areas responsible for processing receptive auditory–specifically language–information. This is when a thorough central auditory processing (CAP) evaluation is recommended.
In the case of children, especially in their formative speech and language acquisition years, an auditory processing disorder (APD) can have disastrous effects on the appropriate acquisition of auditory language, which, in turn, can cause defects in expressive language production, resulting in speech articulation problems, vocabulary and grammar problems, handwriting issues, proper stress and intonation (prosody), as well as sequencing and auditory memory. Kids with otherwise good math skills may crumble in solving word math problems due to the high linguistic content. It logically follows that, since we reproduce what we “hear,” disordered perceptions resulting from an APD will cause output errors in expressive language. Heredity and recurrent middle-ear infections (with attendant reduced hearing acuity/CANS stimulation) are common contributors to CAPD in otherwise-normal children. Click here to read APD expert, Dr. Teri Bellis giving valuable information about this condition in children.
In some adults, CAPD may have been a factor most of their lives, just undiagnosed–especially in those who experienced significant difficulties in their educational history. Acquired APD can also result from head injuries, or acquired peripheral hearing loss (with resultant lack of auditory stimulation to the CANS areas), neurological disease, and from the normal processes of aging. Adults with pre-existing APD will frequently experience out-of-proportion hearing difficulty when their peripheral hearing becomes even marginally degraded due to aging or noise exposure. Research also indicates a significant increase in acquired APD among some menopausal women.
It should be noted that CAPD is not technically a solitary, unified disorder, but actually represents a group of clinical entities which–individually or collectively–create communicative difficulties for a patient. Symptoms like poor speech-in-noise performance, temporal processing problems, “amblyaudia” (abnormal integration of the signals from the two ears in the brain), spatial processing disorder (SPD), phonemic decoding; etc., represent some of the clinical manifestations that are called CAPD. Professional diagnosis by a qualified Neuro-audiological specialist is critical.
This has been a brief primer in CAPD, not an exhaustive exposition of this broad, complex topic. For an excellent book written for non-professionals, get When the Brain Can’t Hear by Dr. Teri Bellis, a renowned researcher and professor in this field. But of particular interest is that Dr. Bellis–who writes academic textbooks on this subject–herself has an APD after a car accident left her with traumatic brain injury (TBI). Her insights, both as patient and professional, give a unique and invaluable insight into this complex disorder. It is available in print and eBook versions. See Amazon.com for more information.
Hopefully this brief overview has given you some insights into CAPD. Next, we’ll take at look at some of the symptoms and behaviors which are possible indicators of an APD and the need for a thorough hearing evaluation, which, if normal, should be followed by a comprehensive CAPD evaluation. Call our toll-free number to schedule evaluation appointments or telephone consulations. We also offer a free half-hour consultation to screen for the need to pursue CAPD evaluation and possible treatment (Formal decision can’t be finalized until the outcome of an audiological evaluation.
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