Psychoelectric measurements and results from cochlear implant patients

Psychoelectric experiments, including threshold, uncomfortable loudness level, loudness growth and frequency discrimination were performed with six cochlear implant patients. All subjects used a single-channel transdermal induction coil implant system. Stimuli were presented directly to the external induction coil and not through a signal processing device. A method is reported in which current at the electrode is derived from voltage measures at the external coil. The derived thresholds were on the order of 1 to 120 microA peak-to-peak and are similar to those reported by other investigators. Loudness growth was more rapid for implant patients, being over twice that of normal listeners. Frequency difference limens were determined using both analog and 16 kHz amplitude modulated signals. Frequency discrimination was better with the analog system than with the 16 kHz amplitude modulated system. In general, below 100 Hz the patients' difference limens were essentially normal, but rapidly deteriorated until at approximately 600 Hz there was little frequency discrimination.