The contribution of static and dynamically varying ITDs and IIDs to binaural detection

This paper investigates the relative contribution of various interaural cue s to binaural unmasking in conditions with an interaurally in-phase masker and an out-of-phase signal (MoS pi). By using a modified version of multipl ied noise as the masker and a sinusoid as the signal, conditions with only interaural intensity differences (IIDs), only interaural time differences ( ITDs), or combinations of the two were realized. In addition, the experimen tal procedure allowed the presentation of specific combinations of static a nd dynamically varying interaural differences. In these conditions with mul tiplied noise as masker, the interaural differences have a bimodal distribu tion with a minimum at zero LID or ITD. Additionally, by using the sinusoid as masker and the multiplied noise as signal, a unimodal distribution of t he interaural differences was realized. Through this variation in the shape of the distributions, the close correspondence between the change in the i nteraural cross correlation and the size of the interaural differences is n o longer found, in contrast to the situation for a Gaussian-noise masker [D omnitz and Colburn, J. Acoust. Sec. Am. 59, 598-601 (1976)], When analyzing the mean thresholds across subjects, the experimental results could not be predicted from parameters of the distributions of the interaural differenc es (the mean, the standard deviation, or the root-mean-square value). A bet ter description of the subjects' performance was given by the change in the interaural correlation, but this measure failed in conditions which produc ed a static interaural intensity difference. The data could best be describ ed by using the energy of the difference signal as the decision variable, a n approach similar to that of the equalization and cancellation model. (C) 1999 Acoustical Society od America. [S0001-4966(99)03808-4].