Psychophysics of binaural hearing - Effects of inconsistent binaural cues Ian Wiggins and Bernhard Seeber MRC Institute of Hearing Research, Nottingham, NG7 2RD, UK There are well established advantages to having two ears for understanding speech in noise, locating sound sources, and functioning in reverberant rooms. These advantages are obtained by exploiting differences in the sound arriving at each ear — interaural time differences (ITDs) and interaural level differences (ILDs). Thus people with hearing loss in both ears might benefit substantially from the use of two hearing aids. However, this requires that the hearing aids present useful binaural cues in light of an individual’s hearing loss. A starting point is to preserve natural binaural cues through the various signal processing stages. Dynamic-range compression is a type of signal processing routinely used in modern devices. When compression acts independently at each ear, ILDs are altered, introducing inconsistency between ITDs and ILDs. We have investigated the perceptual consequences of this type of processing in normal-hearing listeners using virtual acoustic stimuli. A first experiment studied the impact on the spatial attributes of sounds using a questionnaire method, and a second experiment looked for corresponding effects in judgements of lateral position. Compression generally shifted sounds towards a more central position, consistent with a reduction in ILDs. For sounds containing gradual onsets and offsets, including speech, compression generated dynamic ILD changes at rates low enough to be followed perceptually. In such cases, the perceptual effects were more severe: listeners often reported moving and/or split images, and the separation between the reported leftmost and rightmost extents of the sound increased substantially. Compression also resulted in slightly poorer externalization of sounds. The severity of the effects was reduced when undisturbed low-frequency binaural cues were made available. The studies identified specific conditions in which unsynchronized bilateral compression severely alters spatial attributes of the sound and thus it found situations in which both ITDs and ILDs should be preserved.