Effect of deep insertion of the cochlear implant electrode array on pitch estimation and speech perception

Deeply inserted electrodes offer the possibility that apical stimulation may improve speech performances. Therefore, deep insertion is reasonable and should be performed in patients with profound or total hearing loss.

To evaluate the importance of insertion depth beyond 25 mm in a group of cochlear implant patients with deeply inserted electrodes up to 32 mm.

In the first part of the study patients were asked to perform a pitch estimation for channels across the whole length of the electrode array. We evaluated whether pitch discrimination was possible along the whole cochlea and especially in its apical part. Then, the audiological performances of 10 patients were tested in 5 conditions, in which we artificially varied the insertion depth in each patient by activating and deactivating channels. The patients were tested immediately in the new condition to avoid adaptation.

The results showed that activating the electrodes in the uppermost region of the cochlea improves speech perception significantly. Furthermore it could be demonstrated that the pitch perceived in the cochlea with electrical stimulation decreases with increasing insertion depth along the whole length of deeply inserted electrode arrays.