Training-induced improvements on interaural level difference (ILD) and interaural time difference (ITD) discrimination in human adults

Abstract

The two primary cues to the location of sound sources on the horizontal plane are interaural level differences (ILDs) and interaural time differences (ITDs). The malleability of the processing of these two cues in humans was investigated by examining how multiday practice affects the discrimination of different values of ILDs and ongoing ITDs presented over headphones in adults with normal hearing. On average, the listeners improved on both ILD and ITD discrimination, but the learning patterns differed between the two cue types. Improvement was initially rapid for both cue types and appeared to generalize broadly across conditions, suggesting procedural learning. However, a subsequent slower‐improvement stage occurred solely for the ILD cue and showed some specificity to the stimulus used during training. Interestingly, for ILD discrimination, both the best and worst daily threshold estimates decreased with multiday training, indicating an improvement in fundamental processing capacity. In contrast, for ITD discrimination, the best threshold estimates remained unchanged but the worst decreased, suggesting an increased ability to access already existing capacities. One interpretation of these data is that training mediates the processing of ILDs and ITDs at a stage in the auditory pathway, where these two cues are processed separately. [Work supported by NIH/NIDCD.]