Binaural masking level differences in nonsimultanuous masking

This chapter investigates the extent to which binaural unmasking occurs with nonsimultaneous presentation of masker and signal, particularly in forward masking. The majority of previous studies that addressed this question found that there is a substantial binaural masking level difference (BMLD) in forward masking even for fairly long signa! delays, but that the amount decreases with increasing temporal separation between masker and signa!. The existence of a BMLD at long delays is difficult to explain by theories of binaural interaction. Afew studies, on the other hand, reported a substantial BMLD only for short delays between masker offset and signa!. To further examine these conflicting findings, forward-masking curves were measured for a 10-ms 5OO-Hz signal in the conditions NoSo and NoS¿. The masker was a bandpass frozen noise (2O Hz-l kHz) with a duration of either 2O or 300 ms. In an additional condition, a series of frozen-noise pulses of 2O-ms duration and 30-ms interpulse separation was used as the masker. A comparison ofthe results from the two interaural conditions showed a significant BMLD in simultaneous conditions and for the first 10-20 ms of the forward-masking curve but not for longer signal delays. Thus, the BMLD in forward masking was restricted to the short period after masker offset that corresponds to the decay time ofthe basilar-membrane filter at low frequendes.