ELECTRICALLY-EVOKED WHOLE NERVE ACTION-POTENTIALS IN INERAID COCHLEARIMPLANT USERS - RESPONSES TO DIFFERENT STIMULATING ELECTRODE CONFIGURATIONS AND COMPARISON TO PSYCHOPHYSICAL RESPONSES

Electrically evoked whole nerve action potentials (EAP) have been reco rded from 20 Ineraid cochlear implant users in response to bipolar and /or monopolar electrical stimulation of the cochlea. EAP growth functi ons and refractory recovery functions were obtained for a variety of d ifferent stimulating conditions. Where possible, parallel psychophysic al experiments were conducted that measured the just detectable increm ent in stimulus current level (JND), forward-masking functions, and de tection thresholds for a range of different stimuli. Variations in EAP threshold, slope of the EAP growth function, and the rate of recovery of the EAP from the refractory state were observed both across subjec ts for a given place and by mode of stimulation (bipolar versus monopo lar), as well as across electrodes within a subject. A poor correlatio n between slope of the EAP growth functions and current JNDs was obtai ned. However, good correlations were observed between EAP threshold an d psychophysical detection threshold and between the EAP refractory re covery functions and the psychophysical forward-masking functions. Our interpretation of these findings is that these particular physiologic al measures are related to the excitability of the auditory nerve to e lectrical stimulation and further that these measures are related to p erformance of cochlear implant patients on listening tasks. Consequent ly, such information may prove to be useful in adjusting the stimulati on parameters of the cochlear implant speech processor in order to max imize an individual's performance with the device.