ACOUSTIC AND ELECTRIC FORWARD-MASKING OF THE AUDITORY-NERVE COMPOUND ACTION-POTENTIAL - EVIDENCE FOR LINEARITY OF ELECTROMECHANICAL TRANSDUCTION

We investigated electro-mechanical transduction within the cochlea by comparing masking of the auditory nerve compound action potential (CAP ) by acoustical and electrical maskers. Forward-masking of the CAP ref lects the response to the masker of the cochlear location tuned to the probe. Electrical stimulation was delivered through bipolar stimulati ng electrodes within the basal turn of the scala tympani. The growth o f masking of high-frequency probes which excite cochlear locations clo se to the stimulating electrodes was similar for both acoustic and ele ctrical maskers, suggesting a linear transduction of electrical energy to mechanical energy. Exposure to intense acoustic stimulation caused an equal loss of sensitivity to acoustic and electrical maskers. Mask ing of lower-frequency probes by electrical maskers increased rapidly with masker current, suggesting the direct electrical stimulation of n eural elements. This masking was reduced by the administration of stry chnine suggesting a contribution by the efferents towards masking of t hese low-frequency probes.