Extracochlear electrical stimulation.

Extracochlear electrical stimulation was carried out in 7 patients. We used square-wave signals. Electrode positions at the oval and round window showed the lowest current thresholds. The threshold of sound sensations elicited by electrical stimulation was higher in the high frequency than in the low frequency range. All 7 patients had hearing sensations for electrical stimulation with frequencies from 75 Hz to 1 000 Hz, 4 of them to 3 000 Hz. Varying the frequency of the electric signals gave variations of pitch sensation. A higher input amplitude gave variation in pitch sensation in some patients even if the electric frequency remained constant, at least for frequencies below 500 Hz. It seems possible to give prosodic information by transforming the speech from a microphone into electric pulses. This may be especially valuable information of the intelligibility of speech when combined with lip reading.