gms | German Medical Science

Introduction: Electric-acoustic stimulation (EAS) provide great benefits for CI-users with low-frequency residual hearing. However, cochlear implantation remains traumatic and carries the risk of causing high-frequency hearing loss after implantation. For this reason EAS is only recommended for patients with limited residual hearing at low frequencies. Extracochlear electrical stimulation has the potential to minimize cochlear trauma, thus providing benefits of electrical stimulation to a larger number of patients with substantial residual hearing. However, it is not known to what extent extracochlear electric stimulation can be used in conjunction with residual hearing.

The purpose of this study is to investigate potential benefits of extracochlear electrical stimulation combined with acoustic stimulation. For this, the feasibility of extracochlear electrical stimulation at the round window was examined in CI users with partially inserted electrode arrays. Furthermore, the benefit of single electrode basal electric stimulation in combination with acoustic stimulation was investigated. Speech understanding as well as consonant identification performance was evaluated with and without electrical stimulation in normal hearing (NH) subjects using vocoder simulations as well as in CI users.

Potential benefits of single electrode extracochlear electric stimulation was evaluated in NH subjects using vocoder simulation as well as in a unique population of CI users that retain acoustic hearing after partial cochlear implantation. We refer to this subjects partial insertion CI users. In these subjects some electrodes of the CI are placed inside and some others outside the cochlea, so that it is possible to investigate benefits of electrical stimulation delivered through electrodes located close to the round window. Improvements in speech understanding and logatome identification using single electrode electric stimulation was evaluated in 5 NH subjects using vocoder simulations as well as in 5 partial insertion EAS users. Low-frequency information of speech was delivered up to a cutoff frequency via acoustic stimulation. High-frequency information of speech above the cutoff frequency was delivered either acoustically using a single-channel vocoder (in NH subjects) or via electrical stimulation through single CI electrodes located close to the round window (in partial insertion EAS users).

The results of the study show that speech reception thresholds obtained from low-frequency acoustic hearing significantly improved by approx. 8 dB signal to noise ratio (SNR) on average if combined with simulated single channel electrical stimulation in NH subjects (p=0.022). A trend towards improved consonant identification (12% on average) was observed for the same listening condition. Preliminary results in partial insertion EAS subjects showed that extra-cochlear electric stimulation can improve consonant recognition.