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This Article Full Text Full Text (PDF) All Versions of this Article: 100/1/92    most recent 01114.2007v1 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 HighWire Google Scholar Articles by Middlebrooks, J. C. PubMed PubMed Citation Articles by Middlebrooks, J. C.

Cochlear-Implant High Pulse Rate and Narrow Electrode Configuration Impair Transmission of Temporal Information to the Auditory Cortex

Department of Otolaryngology Head and Neck Surgery, Kresge Hearing Research Institute, University of Michigan, Ann Arbor, Michigan

Submitted 8 October 2007; accepted in final form 25 April 2008

In the most commonly used cochlear prosthesis systems, temporal features of sound are signaled by amplitude modulation of constant-rate pulse trains. Several convincing arguments predict that speech reception should be optimized by use of pulse rates 2,000 pulses per second (pps) and by use of intracochlear electrode configurations that produce restricted current spread (e.g., bipolar rather than monopolar configurations). Neither of those predictions has been borne out in consistent improvements in speech reception. Neurons in the auditory cortex of anesthetized guinea pigs phase lock to the envelope of sine-modulated electric pulse trains presented through a cochlear implant. The present study used that animal model to quantify the effects of carrier pulse rate, electrode configuration, current level, and modulator wave shape on transmission of temporal information from a cochlear implant to the auditory cortex. Modulation sensitivity was computed using a signal-detection analysis of cortical phase-locking vector strengths. Increasing carrier pulse rate in 1-octave steps from 254 to 4,069 pps resulted in systematic decreases in sensitivity. Comparison of sine- versus square-wave modulator waveforms demonstrated that some, but not all, of the loss of modulation sensitivity at high pulse rates was a result of the decreasing size of pulse-to-pulse current steps at the higher rates. Use of a narrow bipolar electrode configuration, compared with the monopolar configuration, produced a marked decrease in modulation sensitivity. Results from this animal model suggest explanations for the failure of high pulse rates and/or bipolar electrode configurations to produce hoped-for improvements in speech reception.

This article has been cited by other articles:

				J. C. Middlebrooks Auditory Cortex Phase Locking to Amplitude-Modulated Cochlear Implant Pulse Trains J Neurophysiol, July 1, 2008; 100(1): 76 - 91. [Abstract] [Full Text] [PDF]