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This Article Full Text Full Text (PDF) All Versions of this Article: 99/5/2390    most recent 00751.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Smith, Z. M. Articles by Delgutte, B. Search for Related Content PubMed PubMed Citation Articles by Smith, Z. M. Articles by Delgutte, B.

Sensitivity of Inferior Colliculus Neurons to Interaural Time Differences in the Envelope Versus the Fine Structure With Bilateral Cochlear Implants

¹Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts; ²Speech and Hearing Bioscience and Technology Program, Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts; ³Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts; and ⁴Research and Applications, Cochlear Americas, Englewood, Colorado

Submitted 5 July 2007; accepted in final form 17 February 2008

Bilateral cochlear implantation seeks to improve hearing by taking advantage of the binaural processing of the central auditory system. Cochlear implants typically encode sound in each spectral channel by amplitude modulating (AM) a fixed-rate pulse train, thus interaural time differences (ITD) are only delivered in the envelope. We investigated the ITD sensitivity of inferior colliculus (IC) neurons with sinusoidally AM pulse trains. ITD was introduced independently to the AM and/or carrier pulses to measure the relative efficacy of envelope and fine structure for delivering ITD information. We found that many IC cells are sensitive to ITD in both the envelope (ITD_env) and fine structure (ITD_fs) for appropriate modulation frequencies and carrier rates. ITD_env sensitivity was generally similar to that seen in normal-hearing animals with AM tones. ITD_env tuning generally improved with increasing modulation frequency up to the maximum modulation frequency that elicited a sustained response in a neuron (tested 160 Hz). ITD_fs sensitivity was present in about half the neurons for 1,000 pulse/s (pps) carriers and was nonexistent at 5,000 pps. The neurons that were sensitive to ITD_fs at 1,000 pps were those that showed the best ITD sensitivity to low-rate pulse trains. Overall, the best ITD sensitivity was found for ITD contained in the fine structure of a moderate rate AM pulse train (1,000 pps). These results suggest that the interaural timing of current pulses should be accurately controlled in a bilateral cochlear implant processing strategy that provides salient ITD cues.