FORMANT FREQUENCY DISCRIMINATION AND RECOGNITION IN SUBJECTS IMPLANTED WITH INTRACOCHLEAR STIMULATING ELECTRODES a

Our group in the Coleman Laboratory has studied a subject implanted with 16 intracochlear scala tympani stimulating electrodes. A single-channel analog processor was tested. The processor consisted of a microphone, preamptifier, an instantaneous log compressor, and a linear filter, in that order. The linear filter reduced the low-frequency energy below 200 Hz and pre-emphasized the higher frequencies at about 6-12 dB/octave. Each of the two poles of the single-channel processor was attached to eight of the 16 wires of the electrode array. One pole was connected to the more medial eight electrodes and one pole was connected to the more lateral eight electrode contacts. The subject (L.Y.) was evaluated with standard speech intelligibility tests, basic psychophysical tests, and tests designed to determine what features of the speech signal were used by the subject to understand speech. The subject exhibited surprisingly good performance in understanding speech without the aid of lipreading. Without lipreading, the subject could recognize about 50% of the key words in CID (Central Institute for the Deaf) everyday sentences.I In a four-choice vowel-recognition task, the subject could consistently identify 50-60% of the monosyllabic words that were spoken (n = 60). Experiments, reported here, were conducted to estimate which acoustic features were being utilized by this subject with a cochlear implant.