A Comparison of Extratympanic versus Transtympanic Recordings in Electrocochleography

Detection thresholds, amplitudes and input output curves of cochlear microphonics (CMs), and action potentials (APs) determined by extratympanic electrocochleography (ET ECochG) were compared with those determined by transtympanic (TT) ECochG in the same ears. Two groups were studied: 12 ears in 9 volunteers with normal hearing, and 6 ears in 6 subjects with sensorineural hearing loss. Short tone bursts with frequencies of 0.5, 1, 2 and 4 kHz were used as acoustic stimuli to evoke CMs, and a click was presented to measure the APs. In both groups, although the two approaches produced large differences in amplitudes, nearly identical values were obtained for the CM and AP detection thresholds. The CM and AP input-output curves obtained from mean amplitudes at each intensity in normally-hearing ears had similar slopes with the two approaches. These findings demonstrate the clinical usefulness of ET ECochG.