Thresholds for sinusoids interaurally in phase (S_0) and antiphase (S_π) were measured in the presence of a diotic notched-noise masker (N_0) as a function of notch width. The signal frequency was 250, 500, 1000, or 2000 Hz. For all signal frequencies, the difference between N_0S_0 and N_0S_π thresholds (binaural masking-level difference, BMLD) decreased continuously as the notch width increased. Model simulations showed that this result cannot be accounted for by a model that only processes the output of the auditory filter centered at the signal frequency, even if the nonlinear behavior of the monaural frequency selectivity or interaural differences in the filter shape are considered. The data were predicted well if a detrimental across-channel process was included, either by an addition of portions of the output of adjacent filters to the output of the on-frequency filter or by a notch-width dependent adverse shift in interaural phase in the binaural stage. The strength of this detrimental across-channel process tends to decrease with increasing signal frequencies.
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