Brainstem Encoding of Aided Speech in Hearing Aid Users with Cochlear Dead Region(s)

Area of Science:

• Auditory Neuroscience
• Speech Processing
• Neuroplasticity

Background:

• Speech is encoded in the cochlea via sinusoidal components, which are processed up to higher auditory centers.
• Cochlear dead regions, areas of little to no excitation, can disrupt speech signal processing.
• Aided speech-evoked auditory brainstem response (ABR) can reveal brainstem encoding of speech, especially in relation to cochlear dead regions.

Purpose of the Study:

• To investigate the effects of cochlear dead regions on speech processing at the brainstem level.
• To assess the impact of long-term hearing aid use on the brainstem's response to speech stimuli in the presence of cochlear dead regions.

Main Methods:

• Measured aided speech-evoked auditory brainstem response (ABR) in 76 ears (30 without dead regions, 46 with dead regions).
• Utilized speech stimuli with varying spectral maxima (low, mid, high frequencies).
• Compared ABR characteristics between ears with and without cochlear dead regions.

Main Results:

• Aided speech-evoked ABR was successfully elicited in all participants.
• Stimuli targeting cochlear dead regions resulted in significantly longer ABR latencies and smaller amplitudes compared to controls.
• Differences were observed for stimuli with spectral maxima at dead regions versus other spectral regions.

Conclusions:

• Cochlear dead regions demonstrably alter brainstem speech encoding, particularly for speech components aligned with these regions.
• Brainstem neuroplasticity and the inherent redundancy in speech signals appear to compensate for the impact of cochlear dead regions in individuals with long-term hearing aid use.