Reweighting of Binaural Localization Cues Induced by Lateralization Training
Normal-hearing listeners adapt to alterations in sound localization cues. This adaptation can result from the establishment of a new spatial map of the altered cues or from a stronger relative weighting of unaltered compared to altered cues. Such reweighting has been shown for monaural vs. binaural cues. However, studies attempting to reweight the two binaural cues, interaural differences in time and level, yielded inconclusive results. In this study we investigated whether binaural cue reweighting can be induced by a lateralization training in a virtual audio-visual environment. 20 normal-hearing participants, divided into two groups, completed the experiment consisting of a seven-day lateralization training in a virtual audio-visual environment, preceded and followed by a test measuring the binaural cue weights. During testing, the participants task was to lateralize 500-ms bandpass-filtered (2-4 kHz) noise bursts containing various combinations of spatially consistent and inconsistent ITDs and ILDs. During training, the task was extended by visual cues reinforcing ITDs in one group and ILDs in the other group as well as manipulating the azimuthal ranges of the two cues. In both groups, the weight given to the reinforced cue increased significantly from pre- to posttest, suggesting that participants reweighted the binaural cues in the expected direction. This reweighting occurred predominantly within the first training session. The present results are relevant as binaural cue reweighting is, for example, likely to occur when normal-hearing listeners adapt to new acoustic environments. Similarly, binaural cue reweighting might be a factor underlying the low contribution of ITDs to sound localization of cochlear-implant listeners as they typically do not experience reliable ITD cues with their clinical devices.