Figure 3.
Effects of electrode position in the cochlea, biphasic pulse (100 μs/phase). A, Excitation profiles (spatial tuning curves) obtained for different narrow bipolar configurations in hearing (left) and deafened (right) cochlea in an example animal. White line shows the threshold in the hearing condition. Asterisk and arrow indicate sites with low thresholds. Changing the position of the active electrodes affected only the CF for the more basal low-threshold site (arrow); the more apical low-threshold site (asterisk) did not change. Deafening resulted in loss of the very sensitive low-CF responses (asterisk) at 4.6 kHz, but the basal response remained discernible and changed corresponding to the position of the active electrodes in the cochlea. B, Effects of stimulation configuration on thresholds in all 11 animals for low-CF sites (apical cochlea) in hearing (blue) and deafened (red) condition. The thresholds increased with basal shift of the active electrodes in both hearing and deafened conditions, but the effect was stronger for the hearing condition. C, Same data for high-CF sites (i.e., basal cochlea). For comparisons, the blue dashed curve represents the change in median threshold with position for the hearing condition in B, and the red line shows the same for the deaf condition in B. In the basal cochlea, the change of thresholds with cochlear position of the active electrode differs from the hearing condition in B, regardless of the hearing status. 40 dBatt correspond to 100 μApp. Two-tailed Wilcoxon-Mann–Whitney test, *∼5% significance level; **∼1% significance level; ***∼0.1% significance level.