The influence of interaural stimulus uncertainty om binaural signal detection

This paper investigated the influence of stimulus uncertainty in binaural d etection experiments and the predictions of several binaural models for suc h conditions. Masked thresholds of a 500-Hz sinusoid were measured in an N rhoS pi condition for both running and frozen-noise maskers using a three i nterval, forced-choice (3IFC) procedure. The nominal masker correlation var ied between 0.64 and 1, and the bandwidth of the masker was either 10, 100, or 1000 Hz. The running-noise thresholds were expected to be higher than t he frozen-noise thresholds because of stimulus uncertainty in the running-n oise conditions. For an interaural correlation close to +1, no difference b etween frozen-noise and running-noise thresholds was expected for all value s of the masker bandwidth. These expectations were supported by the experim ental data: for interaural correlations less than 1.0, substantial differen ces between frozen and running-noise conditions were observed for bandwidth s of 10 and 100 Wt. Two additional conditions were tested to further invest igate the influence of stimulus uncertainty. In the first condition a diffe rent masker sample was chosen on each trial, but the correlation of the mas ker was forced to a fixed value. In the second condition one of two indepen dent frozen-noise maskers was randomly chosen on each trial. Results from t hese experiments emphasized the influence of stimulus uncertainty in binaur al detection tasks: if the degree of uncertainty in binaural cues was reduc ed, thresholds decreased towards thresholds in the conditions without any s timulus uncertainty. In the analysis of the data, stimulus uncertainty was expressed in terms of three theories of binaural processing: the interaural correlation, the EC theory, and a model based on the processing of interau ral intensity differences (IIDs) and interaural time differences (ITDs). Th is analysis revealed that none of the theories tested could quantitatively account for the observed thresholds. In addition, it was found that, in con ditions with stimulus uncertainty, predictions based on correlation differ from those based on the EC theory. (C) 2001 Acoustical Society of America. [DOI: 10.1121/1.1320472].