TOWARDS ELECTRIC AND ACOUSTIC STIMULATION OF THE AUDITORY SYSTEM VIA EAR‑CANAL ELECTRODES

Cochlear implants (CIs) can restore hearing in people with profound sensorineural loss. Combining electric and acoustic stimulation improves speech understanding, but the implantation procedure carries surgical risks and a potential loss of residual hearing.
For this reason, we investigate non-invasive electric stimulation via ear-canal electrodes. Electric stimulation with ear canal probes, such as gold-foil–coated Tiptrodes, can evoke auditory sensations when current is delivered in the ear canal (Zeng et al., 2019); however, this stimulation is frequently accompanied by side effects, including somatosensory responses.
To explore whether electrode material influences these effects, a new electrode concept based on non-polarizable materials has been developed and evaluated alongside conventional gold-foil electrodes.
Two electrode designs with non-polarizable silver/silver-chloride (Ag/AgCl) ink were developed: a fully coated Ag/AgCl ear probe and a striped version, to reduce material usage and improve comfort.
The study tested whether non-polarizable electrodes reduce side effects while eliciting hearing sensations comparable to those produced by polarizable electrodes. Electrical stimulation was performed with sinusoidal signals at 250, 500, 1000, 2000, and 4000 Hz. Normal hearing participants were asked to report subjectively its perceived intensity and loudness on a 0-10 scaling.
Preliminary results in normal hearing subjects receiving electric stimulation through ear canal electrodes indicate that Ag/AgCl electrodes elicit similar auditory sensation as Tiptrodes, while reducing uncomfortable side effects. These results open the possibility to design novel auditory prostheses combining electric ear canal electrodes with acoustic stimulation.