Inter-individual differences in binaural detection of low-frequency or high-frequency tonal signals masked by narrow-band or broadband noise.

Detection thresholds for either 500-Hz tones or 4-kHz tones were measured for a group of 19 listeners utilizing the interaural configurations NoSo and NoS pi. Both broadband (100-8500 Hz) noises and narrow-band (50-Hz-wide) noises served as maskers. In addition, direct measures of the listeners' sensitivities to changes in interaural temporal differences (ITDs) and interaural intensitive differences (IIDs) were measured using 400-Hz-wide noises centered at 500 Hz or 4 kHz. A rather large range of inter-individual differences in threshold was observed for 4-kHz tonal signals masked by narrow-band noise in the NoS pi configuration. This result is consistent with several sets of data from our previous experiments conducted over more than a decade. A broad range of thresholds was also obtained for 500-Hz tonal signals masked by narrow-band noise in the NoS pi configuration. This outcome, coupled with the fact that the use of a broadband masker did not yield a large distribution of thresholds for the detection of a 500-Hz tone masked by a broad band of noise, suggests that it is the use of a narrow-band masker, per se, that results in a large range of thresholds. Statistical analyses revealed that thresholds in the NoS pi detection tasks were not highly correlated with thresholds measured in the ITD- and the IID-discrimination tasks. Nevertheless, the five listeners who were the most sensitive in the narrow-band NoS pi detection and the five listeners who were the least sensitive in the narrow-band NoS pi detection tasks were those who were the most and least sensitive, respectively, to changes in ITDs and to changes in IIDs.