The effects of interaural correlation and interaural place of stimulation asymmetry on binaural fusion

The combination of information at the two ears resulting in the perception of a singular auditory percept is referred to as binaural fusion. The stimulation received by bilateral cochlear implant (CI) users sometimes fails to foster binaural fusion. The goal of this study was to assess, for CI users, the extents to and manners in which interaural correlation of stimulation and the degree of interaural place of stimulation asymmetry affect binaural fusion. Bilateral CI users were presented with 1000 Hz pulse trains modulated by envelopes for which the interaural correlation was manipulated. Additionally, one electrode from one ear was paired with different electrodes from the other ear in order to manipulate interaural asymmetry. Listeners indicated the spatial diffuseness of the sound they perceived and whether they perceived a unitary auditory “image” by rotating a dial to manipulate a visual representation of their perception superimposed on a picture of a human head. Additionally, listeners could move the lateral position of the visual representations left or right, indicating perceived laterality. The results suggest that, independent of the degree of interaural asymmetry, the interaural correlation of the envelope was related directly to the degree of perceived binaural fusion.