Compound action potential and cochlear microphonic extracted from electrocochleographic responses to condensation or rarefaction clicks

In electrocochleography (ECochG) compound action potential (CAP) and summat ion potential (SP) are usually separated from the cochlear microphonic (CM) by the CM cancellation technique consisting in averaging the responses evo ked by rarefaction and condensation elicits. With the aim of analysing the ECochG responses evoked by monophasic clicks, we developed a numerical meth od based on the theory of optimal filtering, which makes no assumptions abo ut the unknown potentials. The application of the filtering technique to th e ECochG recordings obtained from 6 normally hearing children and 10 childr en with cochlear hearing loss allowed us to perform CAP extraction in cases where CM was not cancelled by the conventional method. Differences in SP a mplitude and polarity were found between rarefaction and condensation click -evoked responses in cochlear hearing losses.