Differences between electrode-assigned frequencies and cochlear implant recipient pitch perception

Conclusion. This study demonstrated an evident mismatch between frequencies assigned to electrodes and frequencies evoked by stimulation of those same electrodes in implanted patients. We propose that the mapping procedures should include, whenever possible, a comparison with homolateral residual hearing in order to obtain an appropriate frequency range assignation for each electrode. Objectives. The study aimed to investigate the correspondence between the frequencies assigned to each electrode and those actually perceived by the cochlear implant patient. Patients and methods. We studied five post-lingually deaf adults with detectable residual hearing in the implanted and in the contralateral ear, who had each received a Cochlear (R) implant. An ACE standard setting was used for mapping. The patients were asked to match the electric pitch with the acoustic one following presentation of pure tones to both the implanted and the contralateral ear. Results. In almost all patients the two most apical electrodes evoked higher frequencies than those assigned by the mapping software (E22 = 188 - 313, E21 = 313 - 438 Hz). Therefore, electric stimulation seems not to determine pitch sensations for frequencies < 500 Hz. For most electrodes there is no correspondence between the acoustic pitch and the assigned frequency ranges. Moreover, these results were almost always different when stimulating the implanted and the contralateral ear.