Cortical Measures of Binaural Processing Predict Spatial Release from Masking Performance.

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Neuroimaging

Background:

• Binaural sensitivity, particularly interaural phase difference (IPD) detection, is vital for speech comprehension in noisy environments.
• Current behavioral measures of binaural percepts require extensive training and are not routinely assessed.
• Aging and hearing loss are known to negatively impact auditory processing, including binaural hearing.

Purpose of the Study:

• To investigate auditory evoked potentials (AEPs) as a rapid physiological measure of interaural phase difference (IPD) detection.
• To assess the impact of age and hearing loss on the encoding of IPDs.
• To determine if AEP-based IPD measures predict behavioral spatial release from masking (SRM).

Main Methods:

• Cortical auditory evoked potentials (AEPs) were recorded in response to 180° IPDs embedded in amplitude-modulated tones.
• Experiment 1 included young to middle-aged adults with good hearing; Experiment 2 included older adults with age-related hearing loss.
• Objective AEP measures of IPD encoding were correlated with behavioral measures of spatial release from masking (SRM).

Main Results:

• Participants with good hearing encoded IPDs up to 1,000 Hz, while older adults with hearing loss showed limited encoding above 750 Hz.
• Objective AEP measures of IPD encoding were strongly correlated with and predictive of behavioral SRM.
• AEP measures of IPD encoding were superior predictors of SRM compared to age or hearing loss alone or combined.

Conclusions:

• Auditory evoked potentials (AEPs) provide a rapid and objective measure of binaural sensitivity and interaural phase difference (IPD) encoding.
• Aging and hearing loss significantly limit the frequency range for effective IPD encoding.
• Objective AEP measures are highly predictive of an individual's ability to benefit from spatial cues for speech understanding.