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Primers
Auditory Perception - Page 3, Motion Cues
Localization Resolved by Head Motion
The natural world is a constantly changing environment with respect to both visual and auditory events.   The relative position of sound sources to the listener can be modified in one of two ways:
  1. due to the change in location of the source,
  2. or due to a shift in the listenerís location or orientation.  
Human listeners take advantage of the interactivity with sound sources to more accurately localize them. 

A listener can acquire much information about the location of a source by moving their head.   Such head motions are used for two reasons.  First, head rotation may be used as a pointing device.   A human listener could adjust the head orientation until the source appears to be located in front,


where the localization sensitivity is greatest.   Second, head movement plays a dominant role in resolving confusions for sources located on the cone of confusion.  

To demonstrate this phenomenon, let us consider the case of a stationary source located at 180° in azimuth, as shown in Figure 4.   This situation may create ambiguity as to whether the sound source is located in the back at 180° or in front at 0° due to the ITD and ILD being at 0 for both locations (Figure 4a).  If the sound source is located in back, a head rotation to the left will cause the sound to arrive earlier and with a greater intensity at the left ear (Figure 4b).  If, however, the sound is located in front, the same head rotation to the left will cause the sound to arrive earlier and with a greater intensity at the right ear (Figure 4c). 


Figure 4 Head movements used to disambiguate
the location of sources on the cone of confusion.
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