1992 Volume 35 Issue 6 Pages 659-665
A new model of extracochlear prosthesis has been developed for the profoundly deaf whose auditory nerves are still alive. Simple tests carried out using our extracochlear stimulator in order to investigate what kinds of sensation were elicited by the electrical stimulation. Pt-Ir electrode was attached to the promontory and a return electrode was placed on the earlobe. First, the current threshold was obtained and then two time-sequential patterns were displayed successively to get the time resolution of the auditory nerves. For this test, twenty patients who were profoundly or slightly deaf were subjected.
From these simple tests, it was ascertained that the thresholds and the sensations varied according to the subject. Sensations produced by the stimulation were categorized into two groups. One of them was the sensation like a sound, the other was like a vibration, pain or prickly sensation. Not only auditory nerves but also facial and glossopharyngeal nerves were probably stimulated in this tests. As concerns discrimination between two time-sequential patterns consisting of double pulse series, three patients could clearly distinguish them when the time difference of the double pulse was slightly changed.
Signal processing method which transmits both the pitch and the second formant frequency using time-sequential pattern is one of approaches for the extracochlear prosthesis.