Brainstem auditory-evoked responses. Normal variation as a function of stimulus and subject characteristics.

Brainstem auditory-evoked responses (BAERs) were elicited from 64 neurologically and audiometrically normal adults and 77 normal, full-term neonates with broadband rarefaction or condensation clicks at sensation levels (hearing levels in neonates) of 30 to 70 dB and at rates of ten and 80 clicks per second. In addition to the known effects of rate, previously unrecognized effects of acoustic phase and stimulus intensity on BAER interpeak latencies (IPLs), and an interaction of all three stimulus parameters, were found. Stimulus characteristics, age, and sex can account for much of the inter- and intrasubject variability of BAER IPLs and morphology. The BAER effects of many of these variables and their interactions have not been appreciated in clinical applications of BAER. Recognition and control of such reducible, methodological sources of BAER variability will enhance the sensitivity and specificity of the test in neurologic diagnosis.