Off-Vertical Axis Rotation: Eye Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight, DSO 499 (OVAR) - 11.19.14
ISS Science for Everyone
Science Objectives for Everyone
The Eye Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight (OVAR) study allows for better understanding of normal balance and suggest causes for abnormal balance after space flight.
Science Results for Everyone
We roll our eyes on Earth to express annoyance, but in microgravity, it helps us keep our balance when we feel tilted. Scientists evaluated eye movement in astronauts before and after space flight and found no significant difference, yet the astronauts perceived significantly more tilt immediately after flight. This suggests that the inner ear’s balancing mechanism still works after flight, but that there is a disconnect between that mechanism and our perceptions. The two are likely, therefore, controlled by different parts of the brain. This work will help scientists assess balance disorders and crewmembers keep their balance in space.
French National Center for Scientific Research (CNRS), Toulouse, , France
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
October 2004 - October 2005
Previous ISS Missions
As a DSO, OVAR was performed on crewmembers during ISS Increments 10 and 11.
- The Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight (OVAR) studies the effects of microgravity on the balance-sensing organs of astronauts. Scientists believe that the sensory system that contributes to balance and sense of orientation is one of the systems most affected by gravity.
- Understanding changes in the crewmember’s balance-sensing organs will help scientists assess balance disorders as well as describe readjustments involved with respect to being exposed to a microgravity environment.
The Eye Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight (OVAR) is a Detailed Supplementary Objective (DSO). A DSO is a medical investigation supplementary to the primary investigation performed voluntarily by the crewmembers. DSOs are designed to require minimal crew time, power and stowage; and are focused on studying adaptation to microgravity.
The objective of OVAR is to assess the changes in otolith (small particles found in the inner ear which aid in balance) information processing following adaptation to microgravity by comparing eye movements and the process of the brain by which we understand and interpret the information we receive through the eyes before and after space flight.
The inner ear contains two balance-sensing organs; the semicircular canals (fluid-filled tubes located inside of the ear that control balance) which sense rotation, and the otoliths which sense both translation and position of the head relative to gravity. During rotation at a constant velocity (speed of an object in a certain direction) about an axis (the center around which something rotates) tilted relative to gravity, only the otolith organs are stimulated by the change in head position relative to gravity. Movements of the eye during OVAR will accurately reflect processing of the otolith signals by the brain.
This study will allow for better understanding of normal balance and suggest causes for abnormal balance related to microgravity exposure. In particular, space flight will provide knowledge and understanding of the vestibular system (sensory system that contributes to balance and sense of orientation), which is one of the systems most affected by gravity.
This study will allow for better understanding of normal balance and suggest causes for abnormal balance in patients on Earth. If OVAR, associated with a 3-D eye movement measuring system, proves that reliable information about otolith organs can be obtained, then this test has obvious clinical value to assess vestibular disorders.
OVAR has no inflight requirements.
Eye movements and motion perception will be recorded during OVAR clockwise and counterclockwise at various angles and speeds. Three preflight sessions will occur at three, two, and one month before launch; followed by five sessions postflight on landing day, R+1, R+2, R+4, and R+8 days.
OVAR has the advantage of generating cyclic testing control of OCR, allowing averaged measurements over several cycles, presumably improving measurement accuracy over static head tilt tests. Results show there was no significant difference in OCR during OVAR immediately after landing compared to preflight. However, the perceived degree of the roll tilt during OVAR was significantly larger immediately postflight, and then returned to control values in the following days. Since the OCR response is mainly due to the shearing force exerted on the otoliths by tilt relative to gravity, the absence of change in OCR postflight suggests that the peripheral otolith organs function normally after short-term spaceflight. However, the increased sense of roll tilt indicates an adaptation in the central neural processing of gravitational input, supposedly related to a re-weighting of the internal model of gravity, or lack thereof, as an adaptation to microgravity.
These results suggest a separation between otolith-driven eye movement and orientation perception during passive vestibular stimulation by inertial motion after space flight, and support the conclusion that otolith-driven compensatory eye movement and orientation perception are controlled by different neural mechanisms. OCR is primarily a direct response of otolith activation by low-frequency linear acceleration along the axis between the ears, whereas perception of tilt is primarily governed by the integration of otolith inputs, as well as bodily sensations such as position of limbs and pressure on the skin and internal organs. Apparently, the peripheral vestibular organ showed little or no changes after 10-13 days space flight, thus otolith-driven eye movements appear relatively unaffected by short-term exposure to microgravity. However, the central processing of orientation relative to gravity is likely to be affected and suggests why perceptual and oculomotor responses dependent on central vestibular processing can be greatly disrupted (Clement 2007, 2012).
Clement G, Wood SJ, Wood SJ, Wood SJ. Eye movements and motion perception during off-vertical axis rotation after spaceflight. Journal of Vestibular Research. 2013 January 1; 23(1): 13-22.
Clement G, Denise P, Reschke MF, Reschke MF, Wood SJ, Wood SJ, Wood SJ. Human ocular counter-rolling and roll tilt perception during off-vertical axis rotation after spaceflight. Journal of Vestibular Research. 2007; 17(5-6): 209-215. PMID: 18626132.
Ground Based Results Publications
Wada Y. Why and how we perceive tilt perception in space-an experimental plan during long-term space life in the international space station. Equilibrium Research. 2011; 70(2): 115-121. [Japanese]