The Ambiguous Tilt and Translation Motion Cues After Space Flight (ZAG) investigation will explore physiological mechanisms and operational implications of spatial disorientation and tilt-translation disturbances reported by crewmembers when making head movements during and following re-entry.
ZAG will also evaluate a tactile prosthesis as a countermeasure for improving control of whole-body orientation during passive tilt and translation motion paradigms.
The central nervous system must resolve the ambiguity of inertial motion sensory cues in order to derive an accurate representation of spatial orientation. Adaptive changes during space flight in how the brain integrates vestibular cues with other sensory information can lead to impaired movement coordination, vertigo, spatial disorientation and perceptual illusions following G-transitions. This study is designed to examine both the physiological basis and operational implications for disorientation and tilt-translation disturbances following short duration space flights. Specifically, this study addresses three questions:
1) What adaptive changes occur in eye movements and perception in response to different combinations of tilt and translation motion?
2) Do adaptive changes in tilt-translation responses impair ability to manually control vehicle orientation?
3) Can sensory substitution aids (e.g., tactile) mitigate risks associated with manual control of vehicle orientation?
The first specific aim of this experiment will be to examine the effects of stimulus frequency on adaptive changes in eye movements and motion perception during combined tilt and translation motion profiles. Sinusoidal linear motion will be provided by a Variable Radius Centrifuge (VRC) in the roll plane and by a Tilt-Translation Sled (TTS) in the pitch plane. The VRC paradigm provides otolith and other graviceptor cues regarding tilt orientation without concordant canal cues, which are absent during constant velocity rotation. The TTS paradigm, on the other hand, provides canal cues regarding tilt orientation without concordant otolith cues by maintaining the resultant gravitoinertial vector aligned with the body longitudinal (Z) axis. The second specific aim will employ a closed-loop nulling task in which subjects will be tasked to use a joystick to null out tilt motion disturbances on these two devices. The third specific aim will be to evaluate how a tactile prosthesis can be used to improve control performance. The results of this study will contribute to refining the ability of the tactile prosthesis to improve spatial orientation and navigation and serve as a countermeasure for tilt-translation disturbances following space flight.
Preliminary results indicate that the magnitude of perceived tilt increased during static tilt in roll after space flight. Deterioration in the crewmember to control tilt using non-visual inertial cues was also observed postflight. This is due to the internal model of gravity is decreased postflight. This adaptive change can lead to impaired movement coordination, vertigo and perceptual illusions after landing. Additional information, data and preliminary results from this experiment can be found in the publication cited below. This publication is freely available on line.
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