Binaural Unmasking and Frequency Discrimination

Abstract

Frequency difference limens (DL's) were determined for three observers employing a 300 Hz target signal for NOSO, NOSπ, and NmSm at three sensations levels (SL's) above masked threshold (5, 10, and 15 dB) and two masker levels (20- and 59-dB spectrum level). The size of the frequency difference limen in noise is dependent upon the sensation level at which it is measured, the interaural phase of the target signal and the level of the noise. The difference limen is significantly larger when measured at low sensation levels under high-level noise when the target signal is 180° out of phase. This effect diminishes at higher sensation levels or when noise level is reduced, and does not appear when the signal is in phase or when a monaural noise-signal configuration is used. Masker level has no effect on the size of the DL for NOSO or NmSm but a differential effect was seen for NOSπ at 5 and 10 dB SL under the higher masker level where larger DL's were observed as compared to the lower masker level. Theses results are predictable from previous findings in regard to the band width employed by the auditory system under conditions where masking level differences (MLD's) are observed.