Using both ears synchronously (“binaural hearing”) is critical for understanding speech in noisy environments. Functionally, across-ear signal processing by binaural neurons “turns down” background noise, to “un-mask” sounds of interest. For many hearing-impaired listeners, the process of “binaural un-masking” is absent or dysfunctional. This binaural-processing deficit results in profound difficulties for millions of hearing-impaired listeners worldwide. However, the physiological basis for their impaired binaural processing is unknown. Therefore, currently, the development of effective therapies is severely hampered.

Our previous work focused on binaural neurophysiology in normal-hearing listeners. We discovered a key component of the binaural un-masking process: a physiological source of internal delay between the two ears’ inputs to binaural neurons. These internal delays are created by “cochlear disparities”: systematic on-going timing differences between the two ears’ inputs to binaural neurons. The distribution of these internal delays in normal-hearing listeners “optimally tunes” binaural neurons for listening in noisy natural environments.

Despite the impact of hearing loss on binaural perception, no neurophysiological studies have addressed the effects of cochlear damage on binaural neural coding. Cochlear damage resulting from excessive sound exposure (the most common form of hearing loss) dramatically alters cochlear tuning and timing. Altered cochlear tuning and timing in damaged ears likely shifts the distribution of cochlear disparities, and therefore the distribution of internal delays for binaural processing. We hypothesize this disruption likely “de-tunes” the binaural system from its optimal state, removing the binaural advantage for listening in noisy environments. We will quantify this neural “de-tuning” using a variety of carefully designed acoustic stimuli, while recording activity from individual binaural neurons in small mammals chosen for having similar hearing to humans. This neurophysiological study is a major step toward designing hearing aids and implantable devices that compensate for the disrupted internal delays to restore binaural advantages for hearing-impaired patients.