Auditory System Development and Dysfunction: What Do We Really Know about Childhood Hearing Loss?

udiologists must have a thorough under-A standing of normal auditory system function in order to diagnose hearing impairment and dys-function. This is particularly true for the pediatric audiologist who works with a very young patient who may provide limited behavioral information. This background knowledge should include familiarity with auditory anatomy and physiology, psy-choacoustics, and speech perception. The information comes to audiologists from a wide range of both human and animal studies, from studies of developing and mature auditory systems, and finally , from studies of both normally functioning systems and systems with auditory pathology. The academic background of audiologists provides this information from the first undergraduate class through the final graduate courses. However , in everyday practice, it is the working view of what constitutes an impaired auditory system that determines what audiologists actually do. The purpose of this article is to provide a framework for audiologists to guide their work with infants and children who may have hearing loss. An impaired auditory system may be characterized differently by the use of different criteria for dysfunction. Four different types of criteria will be discussed. These criteria include: a threshold criterion, a disease/dysfunction criterion, an audibility criterion, and an expanded audibility criterion. These criteria may be applied individually or together, depending upon the patient and his o r her needs and presenting problems. In addition , the effects of auditory development on the use of these criteria in practice will be reviewed. The answer to this question will differ, depending upon the questioner and his or her frame of reference. The focus of an anatomist will be structural ; the focus of a physiologist will be functional in relationship to the structures being monitored. The audiologist's view of an impaired auditory system will determine which diagnostic and reha-bilitative procedures are used and why. In general , an audiologist might characterize an impaired auditory system as one that: 1) cannot detect sound at levels we have determined to be normal; 2) has one or more sites of lesion that interfere with auditory function; 3) does not have the entire speech spectrum available for processing ; and 4) has difficulty functioning in a noisy environment. Each of these four characteristics of the impaired system also may be associated with one of the criteria for impairment noted above-a threshold criterion, a diseaseldysfunction criterion , an audibility criterion, and an expanded au-dibility criterion, respectively. Threshold …