Masking produced by broadband noise presented in virtual auditory space

An attempt has been made to relate the masking effects studied under dichotic listening conditions to masking seen in the free field. Rather than use a free-field masking paradigm combined with monaural and binaural listening conditions, broadband maskers presented in virtual auditory space (VAS) have been used. Two virtual locations were tested: One was the right interaural axis (+90 degrees from the anterior midline) and the other was 40 degrees right of the anterior midline. Narrow-band (critical bandwidth) dichotic and diotic maskers were also derived from the VAS masker by bandpass filtering around the test frequency. This procedure preserved the interaural differences within the critical band about the test frequency but removed information outside the critical band. Using a diotic target tone of 0.6 kHz with a narrow-band masker centered on 0.6 kHz there was an increase in signal detection in the dichotic conditions when compared to that attributable to either ear alone. Furthermore, there was no further advantage in signal detection at this target frequency when a broadband VAS masker was used. This suggests that for low-frequency targets, the binaural differences within the critical band about the target frequency are sufficient for effective unmasking. In contrast, for a target frequency of 4 kHz, a dichotic narrow-band masker resulted in a reduction in detection compared to that attributable to either ear. However, detection improved to the level attributable to the far ear when a broadband VAS masker was used. This suggests that information outside the critical band is involved in the unmasking of high-frequency targets.