The use of a temporary extracochlear electrode in preoperative testing of permanent implant candidates

This paper describes hearing and speech perception in 9 post-lingually deaf adults fitted with a temporary single electrode, surgically positioned close to the round window niche. After baseline testing, unaided and aided binaurally with the high-power Phonic Ear PE 845, each subject was admitted to hospital for a period of 7 days. During each test session, stimuli were presented directly to the electrode lead by means of an isolation unit. Current thresholds, upper tolerable limits and gap detection were measured for various acoustical waveforms and stimulus frequencies. A laryngograph was used to test the discrimination of prelinguistic and suprasegmental speech features. The results indicated that the prosthesis could provide acoustic sensations of loudness, pitch and duration that changed with stimulus waveform, level of current and frequency, and a gap threshold less than 50 msec. Lipreading appeared to be a necessary adjunct for consonant discrimination.