Establishing equivalence between acoustic and electrical auditory thresholds: a first step towards hearing via electrostimulation.

Objective: Transmitting auditory information through non-invasive electrical conduction warrants greater investigation for medical, entertainment, and military purposes. The objective of the current study is to establish threshold equivalence between acoustic stimulation, measured in sound pressure level decibels (dB SPL), with electrical stimulation amplitude, measured in milliamperes (mA).

Design and study sample: Sixty-eight participants (55 with normal-hearing and 13 with hearing loss) completed acoustic pure tone audiometric testing at 0.25, 0.5, 1, 2, 4, 8, 10, 12.5, and 16 kHz. 29 normal hearing participants and all 13 hearing loss patients completed electrical pure tone testing to measure electrical auditory thresholds for the same frequencies at three locations (forehead, mastoid, and neck). To enhance the predictive capabilities of the models, 26 normal-hearing participants underwent electrical pure tone testing with three levels of narrowband masking noise to elevate their hearing thresholds.

Results: Predictive regression models between the electrical and air conduction thresholds were developed from the data of the normal-hearing participants at the forehead, mastoid, and neck for all frequencies. Data from hearing loss patients was used to assess the goodness of predictive fit for the regression models.

Conclusions: This is the foundational work necessary for further development of electrical hearing technology.