Comparison of acoustically coupled and mechanically coupled speech

Area of Science:

• Auditory Neuroscience
• Bioacoustics
• Speech Perception

Background:

• Traditional hearing aids process sound acoustically, which can introduce distortions.
• Investigating alternative methods for sound transmission to the inner ear is crucial for improving hearing aid technology.
• Understanding the cochlear microphonic (CM) response to direct mechanical stimulation offers insights into auditory signal fidelity.

Purpose of the Study:

• To compare the perceptual quality of speech delivered via direct mechanical ossicular chain stimulation versus conventional hearing aid processing.
• To evaluate the cochlear microphonic (CM) response to piezoelectric-driven speech signals.
• To assess the mechanical-acoustical displacement equivalency and artifact-free nature of the mechanical stimulation method.

Main Methods:

• Phonetically balanced word lists were delivered via piezoelectric drivers directly to the ossicular chain of anesthetized guinea pigs.
• Cochlear microphonic (CM) responses were recorded and compared with CM from free-field tympanic membrane stimulation.
• Listener discrimination testing and preference evaluations were conducted, with and without masking noise, comparing raw CM recordings, hearing aid processed speech, and mechanically coupled speech.

Main Results:

• Listeners achieved near-perfect scores in discriminating raw CM recordings, even with added masking noise.
• A panel of listeners significantly preferred the sound quality of piezoelectrically initiated, CM-derived speech over speech processed through hearing aids.
• Fiber optic measurements confirmed mechanical-acoustical displacement equivalency and demonstrated the absence of mechanical-electrical artifacts in the direct stimulation method.

Conclusions:

• Direct mechanical coupling to the ossicular chain can deliver speech signals with superior perceptual quality compared to conventional hearing aid amplification.
• The findings suggest that bypassing the tympanic membrane and middle ear structures may reduce signal distortion and enhance auditory experience.
• This approach holds potential for developing next-generation auditory prosthetics that offer more natural sound reproduction.