Some Factors that May Influence the Accuracy of Auditory Brainstem Response Estimates of Hearing Loss

There has always been a need for objective tests that assess auditory function in infants, young children, and/or any patient whose developmental level precluded the use of behavioral audiometric techniques. Although several approaches have been tried, such as acoustic-reflex threshold, middle-latency response, and late auditory-evoked potential measurements, for the past twenty-five years, that need has been met primarily by the measurement of shortlatency auditory-evoked potentials, primarily the auditory brainstem response (ABR). These responses arise from the synchronous discharges from groups of neurons along the lower auditory pathway. As such, they are more easily resolved when the eliciting stimulus is characterized by a rapid onset. These responses also must be resolved in a background of noise, coming from other ongoing neural activity. The combination of stimuli with rapid onsets, which results in the synchronized discharge of responses from several neurons, and time-averaging, locked to the stimulus presentation, helps to resolve these lowlevel auditory-evoked potentials. There are many papers and several reviews currently available describing the use of the ABR to estimate the magnitude and configuration of hearing loss (see, for example, Stapells 2000; Stapells, Picton, Perez-Abalo, Read and Smith 1985; Stapells, Picton and Durieux-Smith 1994; Stapells and Oates 1997; Gorga 1999; Hall 1992, for reviews of the topic). Indeed, there is little new information on ABRs since these reviews were published. What is new is the use of steady-state evoked potentials, which is the topic of