Electrically evoked auditory brain stem responses (EABR) and middle latency responses (EMLR) obtained from patients...

Electrical auditory brain stem responses (EABR) and electrical middle latency responses (EMLR) were recorded from patients who had received the Nucleus multichannel cochlear implant system. Twenty-five sequential patients had either intraoperative or outpatient EABR testing. We also recorded EMLRs from several outpatients. EABR results were consistent among all patients tested. Wave V mean latencies were the shortest (3.82 msec) for the most apical electrode (E20) and increased slightly for the medial (E12) and basal (E5) electrodes (3.94 and 4.20 msec, respectively). Absolute latencies for all EABR component waves were observed to be 1 to 1.5 msec shorter than typical acoustic auditory brain stem response (ABR) mean latencies. We have examined the relationships between patients' EABR/EMLR and their behavioral responses to electrical stimulation. Generally, the behavioral threshold and comfort current levels were lower than the predicted values based on EABR/EMLR findings. This observation may be due in part to psychophysical loudness differences noted for pulse rates of 10 to 500 pulses per second in some of the patients that we have studied in greater detail.