Masking-Level Differences for Pulses

Abstract

The effects of interaural time upon the masked, binaural thresholds of periodic pulses were measured. Two interaural time conditions were considered: namely, zero and one-half the repetition period. Additional parameters were interaural phase of the masking noise (0 rad, π rad, and uncorrelated), noise level (approximately 40 and 60 dB sensation level), and pulse rate (10, 50, 250, and 1000 pps). Listening was via headphones in a sound booth. The thresholds were measured by a modified Békésy technique. At low pulse rates (10 and 50 pps), the results for correlated masking show small, if not negligible, masking-level differences. At the high pulse rates (250 and 1000 pps), masking-level differences comparable to those for pure tones are measured. Like the behavior for tones, the antiphasic conditions are more detectable and the homophasic conditions are less detectable. For both sensation levels, on the other hand, the uncorrelated noise condition shows a measurable masking-level difference at the low pulse rates. Ancillary experiments at low pulse rates, with interaural times of 2 and 6 msec, suggest that detectability is essentially independent of position of the sound image in phenomenological space. This result is one more fact with which any adequate theory of binaural hearing must deal.