A new approach to comparing binaural masking level differences at low and high frequencies

A new experimental technique for studying binaural processing at high frequencies is introduced. Binaural masking level differences (BMLDs) for the conditions N0S pi and N pi S0 were measured for a tonal signal in narrow-band noise at 125, 250, and 4000 Hz. In addition, "transposed" stimuli were generated, which were centered at 4000 Hz, but were designed to preserve within the envelope the temporal "fine-structure" information available at the two lower frequencies. The BMLDs measured with the 125-Hz transposed stimuli were essentially the same as BMLDs from the regular 125-Hz condition. The transposed 250-Hz stimuli generally produced smaller BMLDs than the stimuli centered at 250 Hz, but the pattern of results as a function of masker bandwidth was the same. The patterns of results from the transposed stimuli are different from those of the 4000-Hz condition and, consistent with the low-frequency masker data, generally show higher BMLDs. The results indicate that the mechanisms underlying binaural processing at low and high frequencies are similar, and that frequency-dependent differences in BMLDs probably reflect the inability of the auditory system to encode the temporal fine structure of high-frequency stimuli.