Investigating Speech Intelligibility Capabilities of Electrical Auditory Stimulation.

INTRODUCTION: In military settings, ear-worn communication systems and hearing protection have equal importance, but opposite purposes. It is crucial to provide clear communication signal free of noise that may also be hazardous to hearing. Electrical auditory stimulation is a mode of transmitting high fidelity speech information with an amplitude modulated electromagnetic signal that is sent transcutaneously through electrodes. No traditional ear-worn transducer is needed, offering various locations for receiving auditory information on the head and body. The purpose of the current study is to evaluate the speech intelligibility at different locations on the head and body in quiet and noise.

MATERIALS AND METHODS: Fifty participants total took part in this study with Mayo Clinic IRB approval and informed consent. All completed a pure-tone air conduction hearing test verifying normal hearing. In the first experiment, 20 participants completed electrical word recognition testing in quiet at 3 unique locations using 16-item Modified Rhyme Test (MRT) recordings transmitted through a Tonndorf Audimax Model 500 Audiometer in a repeated measures counter-balanced design. In the second experiment, 30 participants completed testing in quiet as well as in background noise at 3 mastoid-anchored locations, using 68-70 dBA of pink noise presented in the sound field through an immersive Spatial Reality sound system. One-way repeated-measures ANOVA was used for comparing the transformed percent MRT scores between 3 locations on the head, followed by the pairwise comparison of the post-hoc analysis using the t-test. For the second experiment, 2-way repeated-measures ANOVA was used to detect the main effects (location and condition) and interaction, followed by multiple comparisons using paired t-tests.

RESULTS: The percent correct score on the modified MRT tests at the mastoid location during electrical hearing stimulation was statistically significantly greater than at the neck location. Three placements that all had at least one mastoid electrode placement (bilateral mastoid, wrist, and neck) produced very similar MRT scores in a quiet environment. The 2-way repeated measures ANOVA performed on the transformed MRT percent scores showed a significant main effect because of the condition (quiet vs. noise) but did not reveal any significant effect of location. MRT percent correct scores in the noisy condition at all 3 locations were statistically significantly lower than in the quiet condition. All average percent correct scores were greater than 80% in noise.

CONCLUSIONS: Non-acoustic transcutaneous electrical stimulation of the cochlea was shown to perform well in both quiet and noisy environments opening opportunities for future implementations that will help safeguard hearing by decreasing the risk of acoustic damage although maintaining excellent word recognition.

CLINICAL TRIAL REGISTRATION: Identifier: NCT05112809.