localize high frequency sound but not low frequency sound. Binaural localization, however, was possible with lower frequencies. This is likely due to the pinna being small enough to only interact with sound waves of high frequency. It seems that people can only accurately localize the elevation of sounds that are complex and include frequencies above 7,000 Hz, and a pinna must be present. Dynamic binaural cues When the head is stationary, the binaural cues for lateral sound localization (interaural time difference and interaural level difference) do not give information about the location of a sound in the median plane. Identical ITDs and ILDs can be produced by sounds at eye level or at any elevation, as long as the lateral direction is constant. However, if the head is rotated, the ITD and ILD change dynamically, and those changes are different for sounds at different elevations. For example, if an eye-level sound source is straight ahead and the head turns to the left, the sound becomes louder (and arrives sooner) at the right ear than at the left. But if the sound source is directly overhead, there will be no change in the ITD and ILD as the head turns. Intermediate elevations will produce intermediate degrees of change, and if the presentation of binaural cues to the two ears during head movement is reversed, the sound will be heard behind the listener. Hans Wallach artificially altered a sound's binaural cues during movements of the head. Although the sound was objectively placed at eye level, the dynamic changes to ITD and ILD as the head rotated were those that would be produced if the sound source had been elevated. In this situation, the sound was heard at the synthesized elevation. The fact that the sound sources objectively remained at eye level prevented monaural cues from specifying the elevation, showing that it was the dynamic change in the binaural cues during head movement that allowed the sound to be correctly localized in the vertical dimension. The head movements need not be actively produced; accurate vertical localization occurred in a similar setup when the head rotation was produced passively, by seating the blindfolded subject in a rotating chair. As long as the dynamic changes in binaural cues accompanied a perceived head rotation, the synthesized elevation was perceived. Distance of the sound source The human auditory system has only limited possibilities to determine the distance