Binaural masking-level differences with tonal maskers

The thresholds for monaural and binaural 250-Hz test tones masked by a 250-Hz sinusoidal masker were measured as a function of the duration of the test tone. The signal and masker were presented either in-phase or in-quadrature. Next, the just-noticeable degree of amplitude modulation (AM) and just-noticeable modulation index for frequency modulation (FM) were measured as a function of the rate of modulation. Both sets of results suggest that monaural and binaural time constants have similar values (near 100 ms) and that the hearing system does not seem particularly 'sluggish' with the paradigms we used. In a second series of experiments, we again measured the masking of a tone by a tone of the same frequency. Long duration signals were used and we manipulated the phases of the masker and the signal. In order to interpret the results we require no more than the individual just-noticeable difference in level (monaurally about 1 dB) and the just-noticeable interaural time delay (about 100 microseconds at our signal frequency).