Effects of stimulus manipulation on electrophysiological responses of pediatric cochlear implant users. Part II: Rate effects

Electrophysiological thresholds do not accurately predict behavioral thresholds in pediatric cochlear implant users possibly due to differences in rate and duration of pulse presentation. We asked: (1) is there an effect of rate of stimulus presentation on the electrophysiological responses of the auditory brainstem and thalamo-cortex? and (2) can the relationship between electrophysiological and behavioral thresholds be improved by using the same rate of pulse presentation?Behavioral and electrophysiological (EABR and EMLR) responses were elicited for 14 children to single electrical pulses and pulse trains of 2 ms ranging in rate from 500 to 3600 pulses per second (pps).Low rate (500 pps) pulse trains resulted in an increase in EABR wave eIII amplitude and a decrease in wave eV amplitude. Further rate increases resulted in smaller EABR wave amplitudes. EMLR amplitudes were unaffected by increases in rate as were EABR and EMLR latencies. Behavioral thresholds decreased with increasing rate, however, there was no associated reduction in electrophysiological thresholds. Correlation between behavioral and electrophysiological thresholds did not improve by using the same rate of electrical pulse stimulation.Results suggest: (1) higher rates of electrical pulse presentation increase the potential for neural adaptation in the auditory brainstem and (2) using the same rate of electrical pulse presentation does not improve the ability of EABR and EMLR thresholds to predict behavioral thresholds.