When the First Pulse Fades: 75% Reduction in Precedence Effect in Cochlear Implanted Rats.

Area of Science:

• Auditory Neuroscience
• Sensory Systems
• Neuroscience

Background:

• Cochlear implant (CI) users often exhibit impaired binaural hearing, especially in interaural time difference (ITD) discrimination.
• The impact of CI stimulation on the precedence effect (PE) and developmental hearing loss remains understudied.

Purpose of the Study:

• To investigate how CI stimulation affects the precedence effect (PE) by measuring temporal weighting functions (TWFs).
• To compare PE in normally hearing (NH) rats with neonatally deafened (ND) and adult deafened (AD) rats receiving CI stimulation.

Main Methods:

• Behavioral experiments in rats to measure TWFs quantifying the PE.
• Recording lateralization responses to pulse trains with varying ITDs.
• Probit analysis to determine the perceptual weight of each pulse.

Main Results:

• Normally hearing rats showed significant "onset dominance" in TWFs, especially at higher pulse rates.
• CI-stimulated rats (ND and AD) exhibited significantly flatter TWFs, with a ~75% reduction in onset dominance.
• This reduction was more pronounced at higher pulse rates.

Conclusions:

• CI stimulation alters temporal processing related to the precedence effect.
• The findings suggest that the precedence effect may require specific auditory experience, such as exposure to reverberation, to develop properly.
• Abnormal hearing experience during development or later in life impacts auditory processing in CI users.