Bone-conducted stimulation in electrocochleography.
The mechanical vibration patterns close to the cochlea in intact skulls of human cadavers have been studied by means of a miniature accelerometer. A Radioear B70A vibrator and a Brüel & Kjaer Mini Shaker have been used, fed with filtered clicks and with short tone bursts. The tone bursts were found to be superior to the clicks with regard to the vibration spectrum. At 500 Hz a considerable distortion was observed in the accelerometer signal, also when using tone bursts. This distortion was presumably due to resonant vibrations in the skull itself, and may be a source of error not only when using stimuli of short duration as in bone-conduction ECoG but also in conventional bone-conduction audiometry. When the vibrations were applied to the exposed bone surface of the mastoid, vibration levels increased by 10-25 dB compared with when soft tissues covered the point of application. This could be of advantage in bone-conduction ECoG performed at ear surgery.