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Jonathan W Kelly, Andrew C Beall, Jack M Loomis; Postural control without optic flow. Journal of Vision 2003;3(9):213. doi: 10.1167/3.9.213.
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Discrete visual displacement of a room has been shown to cause body sway in adults and cause children to stagger (Lee & Aronson, 1974; Lee & Lishman, 1975). Sinusoidal displacement has been shown to cause body sway at the frequency of the room motion (Dijkstra, et al, 1994). Presumably this effect is due to an attempt to stabilize posture with respect to the external environment. Our experiments tested the idea that visually controlled postural stabilization may occur in the absence of optic flow. To investigate this, we measured postural response to a moving room presented in virtual reality. Subjects viewed either a luminance-defined dioptic environment containing smooth optic flow or a rapidly scintillating random dot cinematogram (SRDC) environment (Julesz, 1971), devoid of any optic flow relating to the task. The SRDC environments consisted of a sequence of random-dot stereograms with single-frame lifetimes, which to each eye appeared as a scintillating dot display of uniform density. Thus, the SRDC stimulus contained no optic flow related to the motion of the room. In both conditions, subjects stood 30 cm. from the wall of a room that oscillated longitudinally at 0.2 Hz. with an amplitude of 10 cm. An optical tracking system measured body sway during exposure to both a moving and stationary (control) room. Spectral analysis of the body motion data revealed significant body sway at the frequency of the visual stimulus (0.2 Hz) for both dioptic and SRDC conditions. During dioptic exposure, room motion produced body sway amplitude that was 5.6 times greater than the control condition. Similarly, SRDC exposure resulted in sway amplitude that was 2.4 times greater than the control. These data suggest that optic flow is not necessary for visual control of posture. Rather, perceived motion regardless of how it is evoked drives postural control.
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