Assessment: scientific foundation.

There are a number of factors currently influencing pediatric hearing assessment. The trend toward universal newborn hearing screening and very early identification suggests that we will be assessing hearing of young infants in larger numbers than ever before. As a result, there will be an increasing need for reliable and valid assessment methods for infants. In particular, it is important that we have the means for estimating frequency-specific and ear-specific thresholds. In addition, there is a need to gather information on other aspects of auditory processing in infants to help us in making our amplification and management decisions. This article focuses on issues not only related to scientific foundations of current hearing assessment methods, but also on research that can impact our understanding of the relationship between assessment data and the ability to process meaningful auditory information in the environment. There are several issues to consider in the relationship between research and clinical practice as they relate to assessment and to the link between assessment measures and the process of evaluating and fitting amplification. First, it is important that our clinical assessment measures be supported by normative data. For example, interpreting thresholds of infants and young children in the clinic depends on an understanding of the thresholds that are provided by infants and children with normal hearing. Infants and young children undergo developmental changes in several dimensions of the sensori-perceptual process, any of which can affect the outcome of an audiological assessment. Second, to make better decisions regarding management of hearing impairment, we need to know something about how infants and children use auditory information at various stages of development and what impact reduced hearing sensitivity has on that process. For example, how does an infant with normal hearing process speech and what happens to that capability when the signal is degraded by hearing impairment? Consider the procedures we use for fitting amplification. They are primarily threshold-based prescriptive procedures. Obviously, the greater the reliability and validity of the thresholds obtained, the better the chance that the prescriptive fitting will be appropriate. But threshold-based prescriptive procedures were not developed based on threshold data alone. They are based on a relationship between thresholds and some measure of, or some assumptions about, suprathreshold processing of speech. There are different assumptions underlying different prescriptive procedures, but all of them have as an objective to amplify speech to a level that is comfortable and/or that produces the greatest intelligibility for the listener. Given the number of different threshold-based procedures, it is easy to see that there is no consensus on how thresholds relate to what hearing impaired ears require in terms of amplified speech. Further, most prescriptions are not based on data from infants or very young children. Answering questions related to more complex auditory processes in infants, and the effect of hearing impairment on those processes, almost necessitates laboratory research. Third, in the laboratory setting, variables can be controlled that cannot be controlled easily in a clinical setting. Tracking and/or manipulation of test variables such as trial interval duration, step size, and trial type (stimulus versus control trial) can be done easily in a laboratory setting. As a result, information on the methods used can be gathered in a systematic way. The work done in the laboratory can and should contribute to the development and improvement of our clinical methods. Finally, work that goes on in the laboratory should force us to question some of our assumptions. Hopefully, the following discussion will stimulate us to think differently about some of the issues that are raised. We should never become complacent and assume that we have all of the knowledge and information that we need. Ideally, the relationship between the clinical process and the work that goes on in the laboratory is synergistic. There are different objectives for work in the laboratory and for work in the clinic. However, in the field of audiology, the best work in the laboratory is driven by clinical questions and the best work in the clinic makes use of knowledge that is gained in the laboratory. In cooperative adults and older children, the assessment stage and the beginning of the management and follow-up stage are somewhat distinct. Typically, the assessment stage is complete before the initiation of the hearing aid fitting process, except, of course, for regular follow-up evaluations and/or examinations to evaluate perceived changes in function. However, in the younger child and infant, the process of selecting and fitting hearing aids often must begin before the assessment stage is complete. Development of a complete and valid audiogram of an infant occurs over a period of time. Introduction of amplification can be deemed necessary long before the assessment is complete, so there is an overlapping, highly interrelated process that goes on and it should not be viewed as two separate and distinct processes. Assessment then becomes part of the intervention. This is important because it may impact the choice of assessment method at various points in the clinical process. The four basic assessment methods used with infants and children are auditory brainstem response (ABR), otoacoustic emissions (OAE), aural acoustic immittance and behavioral test methods. After just a brief overview of some recent work in ABR and OAEs, the discussion will focus on acoustic immittance testing and behavioral measures of hearing. (See Sabo, in this issue, for more information on ABR and OAE measures in the clinic.)