Ambiguous Tilt and Translation Motion Cues After Space Flight (Zag) - 06.20.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Ambiguous Tilt and Translation Motion Cues After Space Flight (Zag) investigates the exposure to combined tilt and translation motion profiles for space explorers who have experienced microgravity.
Science Results for Everyone
In space, the brain and inner ear adapt to conflicting input and a person’s inability to sense head tilt in ways that impair physical abilities post-flight. This investigation found that tilt perception and physical control recovered one week after short flights (additional research is needed on long flights). Results are consistent with assumptions that inner ear changes lead to these problems and suggest that the changes have consequences for space operations. A tactile prosthesis was sufficient to return landing-day performance to preflight levels, and with refinement, this prosthesis could serve as a countermeasure for inability to sense tilt, both for astronauts and people with orientation issues on Earth.

The following content was provided by Gilles Clément, Ph.D., and is maintained in a database by the ISS Program Science Office.
Information provided courtesy of the Erasmus Experiment Archive.
Experiment Details


Principal Investigator(s)
Gilles Clément, Ph.D., Lyon Neuroscience Research Center, Lyon, France

Pierre Denise, University of Caen Basse Normandie, Caen, France
Deborah L. Harm, Ph.D., Johnson Space Center, Houston, TX, United States
Millard F. Reschke, Ph.D., Johnson Space Center, Houston, TX, United States
A. Rupert, M.D., Naval Aviation Medical Research Laboratory, Pensacola, FL, United States
Scott J. Wood, Ph.D., Azusa Pacific University, Azusa, CA, United States

Centre National de la Recherche Scientifique, Toulouse, France
Naval Aviation Medical Research Laboratory, Pensacola, FL, United States

Sponsoring Space Agency
European Space Agency (ESA)

Sponsoring Organization
Information Pending

Research Benefits
Information Pending

ISS Expedition Duration
October 2007 - September 2011

Expeditions Assigned

Previous Missions
Zag was first operated on ISS Expedition 16.

^ back to top

Experiment Description

Research Overview

  • The balance system in the inner ear (otoliths) senses both head translation and head tilt relative to gravity. During space flight, head tilt is not sensed; the brain must therefore learn new ways of orienting oneself in weightlessness, which can then lead to disturbances in perceived motion and balance control upon return to Earth's gravity. The purpose of this research is to examine how the brain adapts to conflicting sensory conditions that may result in motion disturbances after space flight. Before and after space flight, subjects are exposed to a combination of body tilt and translation on a sled or a centrifuge. Changes in eye movements and awareness of position will serve to measure how the brain adapts to conflicting motion cues.

  • 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:

  • What adaptive changes occur in eye movements and perception in response to different combinations of tilt and translation motion?

  • Do adaptive changes in tilt-translation responses impair ability to manually control vehicle orientation?

  • 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.

^ back to top


Space Applications
Information Pending

Earth Applications
Information Pending

^ back to top


Operational Requirements and Protocols
ZAG consists of exposing seated upright subjects in darkness to combined tilt and translation motion during tilt and translation disturbances and to measure their eye movements, motion/orientation perception, and manual control performance during preflight and postflight sessions. During these sessions a Tilt-Translation System (TTS) and a Variable Radius Centrifuge (VRC) will be used. Eight subjects will participate in three preflight sessions (L-120, L-60 and L-30 days); the same subjects will participate in four postflight sessions (R+0, R+1, R+4 and R+8).

^ back to top

Decadal Survey Recommendations

Information Pending

^ back to top

Results/More Information

Information Pending

^ back to top

Results Publications

    Clement G, Wood SJ.  Eye movements and motion perception during off-vertical axis rotation after spaceflight. Journal of Vestibular Research - Equilibrium & Orientation. 2013 January 1; 23(1): 13-22. DOI: 10.3233/VES-130471. PMID: 23549051.

    Clement G, Wood SJ.  Motion perception during tilt and translation after space flight. Acta Astronautica. 2013 November; 92(1): 48-52. DOI: 10.1016/j.actaastro.2012.03.011.

    Reschke MF, Good EF, Clement G.  Neurovestibular symptoms in astronauts immediately after Space Shuttle and International Space Station missions  . OTO Open. 2017 October 1; 1(4): 2473974X17738767. DOI: 10.1177/2473974X17738767.

^ back to top

Ground Based Results Publications

^ back to top

ISS Patents

^ back to top

Related Publications

^ back to top

Related Websites
The information on this page is provided courtesy of the ESA Erasmus Experiment Archive.
Columbus Mission - European Experiment Programme

^ back to top


image Test subject in the Variable Radius Centrifuge which will be used during the Zag preflight and postflight sessions, image courtesy of ESA.
+ View Larger Image

image Test subject in the Variable Radius Centrifuge (VRC). Credit NASA
+ View Larger Image