Abnormal binaural fusion disrupts spectral and spatial perception

Binaural fusion is the grouping of sounds heard at the two ears into a single auditory object. This ability is critical for auditory object formation and segregation in realistic auditory environments with multiple sources. For normal-hearing adults, binaural fusion typically occurs for sounds arising from the same sound source, but not different sound sources. In contrast, children and adults with hearing loss can experience abnormal binaural fusion, which disrupts spectral and spatial perception. Some experience little to no fusion, even for the same sound source. Others, including many individuals who use hearing aids and cochlear implants, experience abnormally broad binaural fusion of sounds differing in tone frequency or voice fundamental frequency across the ears, such that sounds evoking pitch differences of up to one to three octaves are fused across ears. Recent findings of illusory phenomena in both spectral and spatial perception associated with abnormal fusion will be presented, with a focus on broad binaural fusion. These phenomena—spectral blending and mis-localization—provide a compelling explanation for a portion of the difficulties that listeners with hearing loss experience with understanding speech in noisy environments.