Sequential auditory grouping reduces binaural pitch fusion in listeners with normal hearing, hearing aids, and cochlear implants

Binaural pitch fusion, the perceptual integration of dichotically presented stimuli that evoke different pitches, can be considered a type of simultaneous grouping. Hence, auditory streaming cues such as temporally flanking stimuli that promote sequential grouping might compete with simultaneous dichotic grouping to reduce binaural fusion. Here, we measured binaural pitch fusion using an auditory streaming task in normal-hearing listeners and hearing-impaired listeners with hearing aids and/or cochlear implants. Fusion ranges, the frequency or electrode ranges over which binaural pitch fusion occurs, were measured in a streaming paradigm using 10 alterations of a dichotic reference/comparison stimulus with a diotic capture stimulus, with fusion indicated by perception of a single stream. Stimuli were pure tones or electric pulse trains depending on the hearing device, with frequency or electrode varied across trials for comparison stimuli. Fusion ranges were also measured for the corresponding isolated stimulus conditions with the same stimulus durations. For all groups, fusion ranges decreased by up to three times in the streaming paradigm compared to the corresponding isolated stimulus paradigm. Hearing-impaired listeners showed greater reductions in fusion than normal-hearing listeners. The findings add further evidence that binaural pitch fusion is moderated by central processes involved in auditory grouping or segregation.