Binaural Masking with Sine-Wave Maskers

The detectability of one binaural tone, masked by another of the same frequency, was measured as a function of the phase difference between them. In one condition, the tone to be detected, the signal, was the same in both ears. In another condition, the signal was inverted at one ear causing a 180° interaural phase difference in the signal. The masking tone was always the same in both ears. It was presented continuously in one experiment, and was gated on and off with the signal in another experiment. In contrast with similar work in which a noise masker was used, binaural signals inverted at one ear are less detectable in some conditions than binaural signals that are the same in both ears: a negative MLD. The negative MLD was largest (about 10 dB) in gated masking conditions and was found to be dependent on signal-masker duration, growing smaller with longer duration. The detectability of interaurally in-phase signals as a function of the phase difference between signal and masker can be accounted for by a simple energy-detection model. However, no existing theory can adequately explain the results obtained with out of-phase signals, although the results suggest the operation of a system with some of the properties of Durlach's equalization-cancellation mechanism.