Some researchers have reported on how sound localization is affected by the temporal variation of the ITD, ILD and SCs. For horizontal sound localization, Perrett and Noble showed that head rotation facilitated sound localization with 2-kHz low-pass noise. They also showed that head rotation facilitated sound localization with the 2- and 4-kHz high-pass noise, but not when short tubes were inserted in listeners' ear canals. The fact that SCs diminished when short tubes were applied suggests that the temporal variation of SCs facilitates median sound localization but that of ILD does not. Under the head-still condition, subjects were instructed to keep their eyes closed and also to hold their head still while the stimulus was being reproduced. Under the head-rotation condition, subjects were instructed to keep their eyes closed but were free to move their head in a horizontal direction while the stimulus was being reproduced.