A NEW ELECTRODE (HN-5) FOR CM MEASUREMENT IN EXTRATYMPANIC ELECTROCOCHLEOGRAPHY

A new electrode (HN-5) for measuring cochlear microphonics (CMs) in ex tratympanic (ET) electrocochleography (ECochG) has been developed. The HN-5 electrode consists of a silver wire 2 mm in diameter and 5.0 cm in length connected to a low noise cable. The HN-5 electrode showed lo w impedance and excellent frequency characteristics. Using the dummy e ar, artefact contamination tests, such as electromagnetic induction an d mechanical vibration, were performed with the HN-5 electrode and var ious other electrodes. In the HN-5 electrode, artefact contaminations were kept within acceptable noise levels, whereas in the smaller elect rodes, the measurable artefact contaminations were larger. The CMs wer e measured from subjects with normal hearing. CM findings obtained usi ng the HN-5 electrode did not differ from those obtained by transtympa nic (TT) ECochG, apart from their amplitude. HN-5 overcame the major d isadvantage of the ET ECochG and provided a very favourable signal-to- noise ratio, resulting in repeatable response signals averaged from th e same relatively small number of samples as those of TT ECochG. This resulted in successful CM measurements of ET ECochG.