An electric frequency-to-place map for a cochlear implant patient with hearing in the nonimplanted ear

Document Type

Article

Abstract

The aim of this study was to relate the pitch of high-rate electrical stimulation delivered to individual cochlear implant electrodes to electrode insertion depth and insertion angle. The patient (CH1) was able to provide pitch matches between electric and acoustic stimulation because he had auditory thresholds in his nonimplanted ear ranging between 30 and 60 dB HL over the range, 250 Hz to 8 kHz. Electrode depth and insertion angle were measured from high-resolution computed tomography (CT) scans of the patient's temporal bones. The scans were used to create a 3D image volume reconstruction of the cochlea, which allowed visualization of electrode position within the scala. The method of limits was used to establish pitch matches between acoustic pure tones and electric stimulation (a 1,652-pps, unmodulated, pulse train). The pitch matching data demonstrated that, for insertion angles of greater than 450 degrees or greater than approximately 20 mm insertion depth, pitch saturated at approximately 420 Hz. From 20 to 15 mm insertion depth pitch estimates were about one-half octave lower than the Greenwood function. From 13 to 3 mm insertion depth the pitch estimates were approximately one octave lower than the Greenwood function. The pitch match for an electrode only 3.4 mm into the cochlea was 3,447 Hz. These data are consistent with other reports, e.g., Boëx et al. (2006), of a frequency-to-place map for the electrically stimulated cochlea in which perceived pitches for stimulation on individual electrodes are significantly lower than those predicted by the Greenwood function for stimulation at the level of the hair cell.

Medical Subject Headings

Acoustic Stimulation; Cochlear Implants; Electric Stimulation; Electrodes, Implanted; Hearing (physiology); Humans; Imaging, Three-Dimensional; Male; Middle Aged; Pitch Discrimination (physiology)

Publication Date

6-1-2007

Publication Title

Journal of the Association for Research in Otolaryngology : JARO

ISSN

1525-3961

Volume

8

Issue

2

First Page

234

Last Page

40

PubMed ID

17351713

Digital Object Identifier (DOI)

10.1007/s10162-007-0071-1

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