Lateralization yields improved binaural fusion in reverberant environments

Binaural fusion reflects the ability to perceive sounds delivered to the two ears as a single auditory image. Although binaural fusion is degraded when the interaural coherence of the signal (i.e., the statistical similarity of the signal at the left and right ear after accounting for interaural time differences) is reduced, adding an interaural level difference (ILD) can promote binaural fusion. Decreases in interaural coherence occur naturally in reverberant environments. This study aimed to determine if binaural fusion decreases with increasing reverberation and if adding ILDs can counter that effect. Twenty typical hearing listeners were tested with sound processed with a set of generic head-related transfer functions, with simulated room reverberation used to vary the interaural coherence of a sound source. Perceived lateralization was manipulated either by artificially superimposing an ILD on the reverberant binaural signals or by moving the source away from the frontal location in the virtual room. Although binaural fusion decreased with increasing reverberation, improvements were seen by moving the sound source to the side in a low-reverberant environment or by adding a large ILD after the reverberant simulation. These results suggest that perceived lateralization improves binaural fusion in reverberant environments. [Work supported by NIH/NIDCD DC018529.]