Binaural interference effects measured with masking-level difference and with ITD- and IID-discrimination paradigms

The results of several studies have demonstrated that the ability to process binaural information within discrete spectral regions may be degraded by the presence of information at other, even remote, spectral loci. This study focused on binaural interference produced by low-frequency noises (centered at 500 Hz) on the processing of interaural disparities within high-frequency bands of noise (centered on 4 kHz). The bandwidths of the interferers and "targets" were either the same (either 100 or 400 Hz) or different (interferer: 100 Hz; target: 400 Hz). Within a single group of listeners, interference was measured with a masking-level difference paradigm (NoSo vs NoS pi), and in ITD- and IID-discrimination tasks. An important feature of the experiments was the utilization, parametrically, in all three tasks, of pulsed and continuous interferers that were either diotic or were interaurally uncorrelated. As reported in previous experiments, the amounts of interference obtained with pulsed interferers were much greater than those obtained with continuous interferers. The present experiment extends that general finding to discrimination of IIDs. In addition, in all three tasks, pulsed, interaurally uncorrelated interferers produced greater amounts of interference than did pulsed, diotic interferers. The patterns of interference effects found across bandwidths and listeners for the four interference conditions (pulsed-diotic, continuous-diotic, pulsed-uncorrelated, and continuous-uncorrelated) in the MLD paradigm were different than those obtained in either the ITD- or IID-discrimination tasks. One factor that may account for the diverging patterns of interference is that the interaural cues produced by adding the S pi signal to the diotic masker fluctuated in magnitude over time. In contrast, the ITDs and IIDs in the discrimination task were static.(ABSTRACT TRUNCATED AT 250 WORDS)