Sound localization in the presence of one or two distracters.

Localizing a target sound can be a challenge when one or more distracter sounds are present at the same time. This study measured the effect of distracter position on target localization for one distracter (17 positions) and two distracters (21 combinations of 17 positions). Listeners were instructed to point to the apparent position of a train of 30-ms noise bursts, presented at 1 of 85 positions in virtual free field. A harmonic complex and a frequency-swept complex tone served as distracters. The two distracters were turned on 40 and 80 ms after the target onset, had temporal envelopes similar to that of the target, and did not overlap temporally with the target. Virtual sounds were synthesized with individual HRTFs. Localization performance degraded as the number of distracters increased from 0 to 2. When the horizontal distance between target and a single distracter was small (i.e., the interaural differences were almost the same), the influence on the apparent position was greater than when they were far apart. In the vertical dimension, there was not a systematic effect of distracter position on target localizability. However, there was a substantial increase in localization error for targets at high elevations (above 30 degrees) when distracters were present.