Localization of a sound signal in the vertical plane under masking conditions

The effect of masker on the localization of a sound source in vertical sagittal plane was investigated in simultaneous masking conditions and in the precedence effect paradigm. In the first case, the stationary signal and the masker were presented simultaneously while in the second case the signal onset was delayed relative to the masker onset. The delay was 2, 4, 8, 20, 40, 80 and 200 ms. The signal and the masker were created from two different uncorrelated noise bursts with a bandwidth of 5 to 18 kHz. Duration of noise bursts were 1 s. The masker was placed above the listeners head at an angle of 90 deg and the signal was placed in front of the listener at an angle of 7.5 deg. Perceived positions of signals under masking conditions were compared with those single of the signal or masker presented separately. It is shown that under the masking conditions the probability of detecting a signal decreased. Listeners could localize the signal at the delay of 80 ms and higher. The probability of detecting the signal at 80 ms delay was 92%. The perceived position of signal in masking condition did not significantly differ from the perceived position of single signal. At delays ranging from 0 to 40 ms, listeners mainly showed a perceived masker position that was shifted toward the signal. The shifted position was significantly different from the perceived position of a single masker.