Binaural interference in lateralization thresholds for interaural time and level differences.

Abstract

Listeners discriminated changes in either interaural time differences (ITDs) or interaural level differences (ILDs) in one noise band (the target) in the presence or absence of an uninformative spectrally-remote second noise band (the interferer). The noise bands had center frequencies of 500 and 4000 Hz and bandwidths of 50 and 400 Hz, respectively. When one band was a target, the other served as an interferer. The interferer was presented either diotically or dichotically with ITDs or ILDs that varied randomly across intervals. "Interference" was defined as occurring if the target thresholds were elevated in the presence of an interferer. For ITD discrimination, interference was greater for the 4000-Hz target than for the 500-Hz target, but for ILD discrimination, interference for the 500-Hz target was greater than or equal to that obtained for the 4000-Hz target. Larger interference effects were obtained when the interferer ITD or ILD was randomly varied, revealing that interference can be large not only for high-frequency targets but also for low-frequency targets with high-frequency interferers. The data are consistent with a model in which listeners combine lateral position across frequency with interaural information weighted according to the accuracy with which positions are encoded in each frequency region.