NON-INVASIVE ELECTRICAL STIMULATION AT BOTH EAR-CANALS EVOKES LATERALIZED SOUND PERCEPTION AS A FUNCTION OF INTERAURAL CURRENT LEVEL DIFFERENCES

Hearing aids often become ineffective in individuals with severe-to-profound hearing loss, leaving cochlear implantation (CI) as the only alternative to restore hearing. However, CI is an invasive procedure with potential damage to residual hearing, which—when preserved—significantly enhances speech perception outcomes in CI patients. Additionally, bilateral CI devices work independently and provide limited interaural time and level difference cues, resulting in poor spatial hearing.
Here we demonstrate in all tested normal hearing subjects (n=4) that bilateral, non-invasive electrical current stimulation at the ear-canals evoke lateralized sound percepts.
First we defined electrical hearing threshold levels and maximum comfortable levels to establish dynamic ranges (DRs) of stimulation for each ear, presenting tones (between 300-2000 Hz), and filtered noise (1500-4000 Hz bandwidth) stimuli during 500 ms.
Then, for the spatial electrical hearing experiment, interaural current level differences (ICLDs) were defined for the subjectively best perceived tone, and the noise, as asymmetric stimulation levels expressed in percentages of DRs (%Left DR/%Right DR). Six ICLD values were tested (100/0, 80/20, 60/40, 40/60, 20/80, 0/100), each repeated 36 times in randomized order. Participants reported perceived lateralization via left or right button presses. Preliminary results reveal that correct responses behave as psychometric functions with the expected sigmoidal shape, indicating systematic lateralization as a function of ICLD.We aim to implement this non-invasive technique together with acoustic amplification in hearing impaired individuals, providing hearing restoration through a bimodal acoustic (low frequencies) and electrical (high frequencies) binaural device.