Brain-stem Auditory-Evoked Responses

To the Editor.— Two articles in your journal about brain-stem auditoryevoked responses (BAERs) emphasized the importance of controlling technical variables in assessing BAER normal variability and defining BAER abnormalities. As shown in Fig 1, the intrasubject "waveform variations" reported by Chiappa et al¹can occur solely as a function of varying acoustic polarity (rarefaction vs condensation) of the click stimuli used. We agree with Chiappa et al that the morphologic variations they described are not clinically important, but suggest that other laboratories beginning to collect their normative BAER data control for the effects of click polarity, since it is a determinant of BAER interwave latency and relative amplitude norms²(Fig 1), as well as of morphology. Our general findings and conclusions about normal BAER variability²closely agree with those of Chiappa et al and, specifically, we have long concurred about the limited diagnostic value of waves VI