Oman York Conference(2001 in press)11/2/01 It was a personal characteristic which remained stable over periods of more than three years Mittelstaedt hypothesized that those who set the bed slightly head up did so to effectively cancel out a headward gravireceptor bias, and noted that the two astronauts who had experienced inversion illusion in orbital flight had head up biases, whereas the other three did not. Pursuing the origin of the bias, he conducted experiments on a short radius centrifuge where the observers could adjust their position relative to the axis of rotation until they felt subjectively horizontal. normal observers felt horizontal when the rotation axis passed hrough their upper chest. Presumably the effect on tilt perception of the centrifugal stimulus to the vestibular otoliths was being SV balanced by centrifugal stimulation of previously unknown gravireceptors located on the other side of the axis of rotation. In er tests on paraplegics nephrectomized patients(Mittelstaedt, 1996), he found evidence that the effect was mediated by mechanoreceptors in the kidneys and large blood vessels of the omen SV+VG It to be verified how well 1-G tilting bed tests of individual gravireceptor Figure 10. Tilting bed test for 1-G gravireceptor bias predict O-G inversion illusion under ational conditions. Als multisensory bias which could conceivably be influenced by 0-G and launch acceleration induced fluid shift, facial edema, and nasal stuffiness not present in the 1-G tilting bed tests. if so, gra bias measured I-G may be somewhat different than that found in flight 4.2 Visual frame Effects. In their classic rod and frame" experiments, Witkin and Asch(1948)asked erect observers in a dark room to set a dimly lit pivoting rod to the sv. The rod was surrounded by a similarly lit square frame, which was tilted 7 28 degrees clockwise or counterclockwise Ith t to G. As depicted Figurel 1. the observer's sv indications consistently deviated in the direction of frame rotation. There were consistent differences between observers in the size SV Figure 11. Rod and Frame TestOman York Conference (2001 in press) 11/2/01 Page 11 It was a personal characteristic which remained stable over periods of more than three years. Mittelstaedt hypothesized that those who set the bed slightly head up did so to effectively cancel out a headward gravireceptor bias, and noted that the two astronauts who had experienced inversion illusion in orbital flight had head up biases, whereas the other three did not. Pursuing the origin of the bias, he conducted experiments on a short radius centrifuge where the observers could adjust their position relative to the axis of rotation until they felt subjectively horizontal. Normal observers felt horizontal when the rotation axis passed through their upper chest. Presumably the effect on tilt perception of the centrifugal stimulus to the vestibular otoliths was being balanced by centrifugal stimulation of previously unknown gravireceptors located on the other side of the axis of rotation. In further tests on paraplegics and nephrectomized patients (Mittelstaedt, 1996), he found evidence that the effect was mediated by mechanoreceptors in the kidneys and large blood vessels of the abdomen. It remains to be verified how well 1-G tilting bed tests of individual gravireceptor Figure 10. Tilting bed test for 1-G gravireceptor bias predict 0-G inversion illusion under bias. operational conditions. Also, B is a multisensory bias which could conceivably be influenced by 0-G and launch acceleration induced fluid shift, facial edema, and nasal stuffiness not present in the 1-G tilting bed tests. If so, gravireceptor bias measured in 1-G may be somewhat different than that found in flight. 4.2 Visual Frame Effects. In their classic “rod and frame” experiments, Witkin and Asch (1948) asked erect observers in a dark room to set a dimly lit pivoting rod to the SV. The rod was surrounded by a similarly lit square frame, which was tilted 28 degrees clockwise or counterclockwise with respect to G. As depicted in Figure11, the observer’s SV indications consistently deviated in the direction of frame rotation. There were consistent differences between observers in the size Figure 11. Rod and Frame Test