Binaural-cue reweighting induced by discrimination training.

Abstract

When localizing sounds, listeners combine the two binaural cues interaural time and level difference (ITD and ILD). The relative weight assigned to each cue is frequency dependent, with ITDs dominating at low and ILDs at high frequencies. However, this weighting changes (e.g., depending on room reverberation or cue reliability). To achieve better spatial hearing in various listener populations, changing the weighting might be advantageous. Previous studies showed that such changes can be induced (e.g., using a lateralization training with visual reinforcement in virtual reality). Here, a new training procedure is introduced, based on a simple auditory-only discrimination task. An experiment evaluated the procedure, consisting of a pretest, three training sessions, and a posttest. Subjects were divided into three groups-one trained by reinforcing the ILDs, one by reinforcing the ITDs, and one no-training control. The training consisted of an adaptive staircase of relative discrimination trials. Stimuli were two consecutive narrow-band noise bursts (2-4 kHz), each presented with a different combination of ITD and ILD. Participants' task was to indicate the perceived location of the second noise burst versus the first. During training, feedback was provided requiring the subject to imagine the sound moving in the trained cue's direction. We observed an increase in reinforced-cue weight for both training groups, but not in the control group, that continued during all three training sessions. Thus, this training method is effective for reweighting in both directions. Moreover, it is individualized, and, since it does not rely on sophisticated equipment, it can be easily accessible for a range of listeners.