Effects of stimulus manipulation on electrophysiological responses in pediatric cochlear implant users. Part I:...

Discrepancies between electrophysiological and behavioral thresholds in cochlear implant users might be due to differences in stimuli such as the duration and rate of the electrical pulse train. In the present study, we asked: Is there an effect of stimulus duration on electrophysiological responses of the auditory brainstem, thalamo-cortex, and behavioral thresholds? In 5 pediatric cochlear implant users, behavioral thresholds in response to electrical pulse trains at 500 pulses per second (pps) were significantly lower for 40ms than 2ms duration pulse trains. Clear electrically evoked auditory brainstem responses (EABR) and electrically evoked middle latency responses (EMLR) were generated by single electrical pulses and 2, 6, and 10ms pulse trains (500pps) in 5 children. There was a linear decrease in the inter-wave latency between the eV of the EABR and the Na of the EMLR as duration increased. No significant effect of duration was found on eV latency relative to the last pulse in the train or Na latency relative to the onset of the stimuli. Behavioral threshold data is consistent with temporal integration of auditory activity. Electrophysiological data indicates that: (a) recognizable EABR and EMLR waveforms can be recorded in response to electrical pulse trains of up to 10ms; and (b) pulse train stimuli have unique effects on the auditory brainstem compared to thalamo-cortical areas.