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support base of its feet. Therefore, the up and down motion of the head can be considered a second order effect, and rotations within the sagittal and coronal planes yield little additional information beyond that obtained from head translations in the transverse plane. In addition, within the context of this study employing a vertical grid stimulus constrained to moving laterally around a cylindrical screen, information about head movement involving these other degrees of freedom could not, in any event, have any effect on the stimulus movement.
Figure 4 presents a graphical depiction of the
geometric relationships between the two acoustic sources and four microphone/detectors projected on to a transverse plane. The subject is standing at the intersection of lines Li and L2 looking at a point (Yp,Xp) on the cylindrical screen. The two acoustic sources, Sp 1 and Sp 2, are positioned on opposite sides of the head at the ends of line Li. The four microphone/detectors, Mic 1 through Mic 4, are positioned at the vertices of a square that is over the head of the subject, thus removing any ambiguity as to which side of the receiver plane the source is on (as discussed above in this section). The distances, D1 through D8, correspond to the eight possible speaker-microphone (sp-mic) pair combinations. These distances are used to calculate the x and Y coordinates of Sp 1 and Sp 2 using the following equation derived from the Pythagorean theorem in Krantz (1985):
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