Bilateral cochlear implants controlled by a single speech processor

Objective: This study aimed to assess, in one profoundly hearing impaired s ubject, potential benefits and limitations in placing bilaterally implanted scala tympani electrode arrays under control of a single speech processor. Study Design: All available stimulation sites in both ears were compared in studies of pitch discrimination and pitch ranking, identifying three bilat eral pairs capable of supporting interaural comparisons with no perceptible difference in pitch. Using those pairs, the subject's ability to lateraliz e sound was studied as a function of interaural time delay and interaural a mplitude difference. Consonant identification scores were obtained fur cont inuous interleaved sampling processors using various unilateral and bilater al combinations of electrodes. Results: For loudness-matched stimuli composed of 50-msec bursts of 80-mu s ec/phase pulses at 480 pulses/sec, the subject was able to identify the ear receiving the earlier onset for interaural delays at least as brief as 150 mu sec for all three matched pairs. For similar simultaneous stimuli, the subject could identify the ear receiving the louder signal for the smallest deviations from loudness-matched amplitudes available from the implanted e lectronics. The consonant studies found no evidence that bilateral stimulat ion per se degrades speech processor performance, even for arbitrary divisi ons of information between the two ears. Additional contralateral as well a s ipsilateral channels were observed to improve speech processor performanc e. Conclusions: The ability of this subject to lateralize sounds on the basis of interaural delay or loudness difference, combined with the consonant ide ntification results. supports further use of coordinated binaural stimulati on to improve cochlear implant users' ability to understand speech, especia lly in the presence of competing speech noise.