An Electric Frequency-to-place Map for a Cochlear Implant Patient with Hearing in the Nonimplanted Ear

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.

Abnormal Binaural Spectral Integration in Cochlear Implant Users

“…However, not all patients adapt to reduce this mismatch. Bimodal CI users are more likely to experience no changes in pitch or even a drop in pitch for all electrodes, exacerbating the mismatch (Reiss et al 2007(Reiss et al , 2011(Reiss et al , 2012a; consistent with this finding, several long-term studies also found electrode pitch to be mismatched to and lower than the frequency-toelectrode allocations (e.g., Blamey et al 1996;Dorman et al 2007). For bimodal CI users, it is possible that instead of or in addition to adapting pitch, the brain adapts BSI to increase fusion of interaurally mismatched inputs to effectively reduce the perception of mismatch.…”

Detection and rate discrimination of amplitude modulation in electrical hearing

“…It is, however, still possible that apical fibers of passage are stimulated by the apical-most electrodes in intracochlear implants in humans. In fact, research on pitch-matching between acoustic and electric hearing suggests that the apical electrodes of the intracochlear electrode are matched to lower pitches than would be predicted based on tonotopic locations (e.g., Boex et al, 2006;Dorman et al, 2007). Thus, it is possible that the apical-most specialized temporal coding neurons proposed by Middlebrooks and Snyder can indeed be excited by apical stimulation of intracochlear electrodes.…”

Radiologic and Functional Evaluation of Electrode Dislocation from the Scala Tympani to the Scala Vestibuli in Patients with Cochlear Implants

“…Electrode arrays designed to position stimulating contacts near the modiolus appear to operate with lower current thresholds than previous devices that were located closer to the lateral wall of the scala tympani. [15][16][17] The charge units of maximum comfortable loudness level of the 2 groups were compared to determine whether an electrode dislocation was associated with higher stimulus charges.…”