Visual Orientation in Unifamiliar Gravito-Intertial Environments
Principal Investigator: Charles M. Oman, Ph.D.
Background: Astronauts working in 0-G must rely much more on vision to maintain their spatial orientation, since inner ear cues no longer signal the direction of "down". Fortunately, crew members who remained seated in the relatively small Soyuz, Mercury, Gemini, and Apollo capsules rarely encountered orientation problems. However crews of the larger Skylab and Shuttle reported occasional disorientation, particularly when they left their seats, and worked in unpracticed, visually unfamiliar orientations. The problem occurred both inside the spacecraft, and also outside, as when performing Extra Vehicular Activity (EVA). Part of the difficulty was due to the natural tendency to assume that the surface seen beneath your feet is the floor. When working "upside down" in the spacecraft, the walls, ceiling, and floors frequently exchanged subjective identities. Also, when viewing another crew member floating upside down in the spacecraft, you often suddenly felt upside down yourself, because of the subconscious assumption carried over from life on Earth that people are normally upright. Fluid shift and gravireceptor bias also contribute, and make some crew members feel continuously inverted, regardless of their actual orientation in the spacecraft. At first it was thought that these striking "inversion" and "visual reorientation illusions" (VRIs) were benign. However, as operational experience accumulated, it became clear that inversion illusions and VRIs could trigger attacks of space motion sickness during the first several days in weightlessness. Though space sickness susceptibility eventually subsides, crew members on long duration flights say VRI episodes continue to occur. Shuttle EVE crewmembers occasionally feel uncomfortable when working upside down in the Shuttle payload bay when it faces the Earth, even though they know they will not "fall" out. Orientation ambiguity also contributes to navigation difficulties, which become particularly apparent to crew members traversing between modules in a large space station such as MIR. Each module provides a local visual frame of reference for those working inside. The modules on MIR are connected at 90 degree angles, so not all the local frames of reference are coaligned. The modules connect together through a central node, with hatches located in the six cardinal directions. Visiting astronauts touring MIR () say it is sometimes difficult to remain oriented, particularly when traversing the node. Even after living aboard for several months, it is reportedly difficult to visualize the 3 dimensional spatial relationships among the modules, and traverse the node instinctively without using memorized landmarks. Crew members learn routes, but most do not develop 3D "survey" knowledge of the station. One crew member says that despite it's three dimensional structure, MIR seemed somehow like a single story house. Visual orientation may be even more of a challenge on the International Space Station, since it has four nodes and numerous modules, many connected at 90 degrees. Many modules have equipment mounted not only on the walls, but also on ceiling and floor. This uses rack space efficiently, but potentially creates dual visual verticals, potentially making VRIs more likely. Disorientation and navigation difficulties are an operational concern in case an emergency evacuation is required in the event of of a depressurization, fire, or power loss. Astronauts say visual experience gained working in unfamiliar orientations during preflight neutral buoyancy and virtual reality (VR) training helps maintain spatial orientation. Our research team has studied VRIs and orientation in astronauts on the 2 week Neurolab mission, using virtual reality stimuli. We plan to study term adaptation effects on the International Space Station. However , no techniques have been developed to quantify individual differences in orientation and navigation abilities, or to assess the effectiveness of spacecraft specific or generic preflight visual orientation training in simulators or virtual reality devices.
Experiments: Our project team is carrying
out an integrated set of experiments, each the responsibility
of a lead investigator. Our goal is to provide a rationale
and validated methodologies for a scientifically based
preflight visual orientation training countermeasure. Why
are some people are more susceptible to disorientation and illusions
? What kinds of visual training strategies are effective ?
York University 8ft. Tumbling Room.
The York Tumbling Room interior furnishings convey visual information on the direction of "down". The scene is sufficiently compelling that a large percentage of gravitationally supine subjects feel upright when the visual vertical is aligned with their body axis (Click on this picture to view and enlarged version).
Subjects gravitational orientation in the York room can be independently controlled.
We are studying the relationship between scene orientation and subject orientation with respect to gravity in experiments in both the York Tumbling room, and a similar virtual tumbling room at MIT.
subjects looking at visual scene through a 45 deg. tilted mirror
Subjects learn to visualize and predict the location of objects presented on video monitors around as when in a variety of different body orientations. Parallel experiments are being conducted in a real environment at TAMU, and a virtual one at MIT.
VR Orientation/Navigation Trainer at MIT. Subjects wearing
VR head mounted display view the interior of a simulated space
station. In navigation experiments, subjects traverse a
route through several modules and nodes, and then indicate the
the direction home. Try
this experiment yourself. ()
How is our sense of direction coded neurally in the brain ? Studies show that animals construct an internal spatial representation of their environment and use this for spatial orientation and navigation. Some of this neural circuitry involves the limbic system. Animals and humans with hippocampal damage are impaired on a variety of visual memory, spatial and navigational tasks. Previous studies have shown that two types of spatial cells in the limbic system code exocentric spatial information. "Place cells" have a response component related to the animal's location in the environment. "Head direction" (HD) cells discharge as a function of the animal's head direction in an earth horizontal plane. (Click on the diagram below to see a clearer version).
Panel A above shows a typical response of a head direction cell in the rat hippocampus. The direction of maximum response ("preferred direction") lies in a fixed direction relative to the visual environment, and varies from cell to cell. The range of firing is typically about 90°, and decreases away from the preferred direction. Rotating visual landmarks around the animal shifts the preferred direction by a corresponding amount. Response is independent of pitch and roll of the animal's head. We are quantifying the three dimensional response characteristics of rats which have been trained to crawl walls, floor and ceiling of special test chambers, such as the one shown in Panel B .
It has remained an open question whether and how place cells and HD cells respond in 3 dimensions in 0-G. To better understand the physiologic basis of 0-G spatial orientation illusions, we are studying HD cell responses during 15-20 second periods of weightlessness aboard NASA's parabolic flight aircraft. Our goal is to see whether and how directional tuning is maintained during both the weightless and hypergravic phases of flight.
Animals are tested in a rectangular plexiglas chamber, gridded on the floor, ceiling, and one wall so the animals can walk in 0-G. If plane of sensitivity remains aligned with the 1-G/1.8G "floor" of the chamber, even when the animal climbs a "wall" in 0-G, it indicates that the plane of sensitivity is determined by the animal's cognitive reference frame, and not simply by the plane of its locomotion. When animals crawl on the "ceiling" of the chamber in 0-G, we look for a reversal in the preferred direction, suggesting that the animal -like an astronaut - has experienced a VRI (Click on the picture to view an enlarged version).
PROJECT 2 REFERENCES
Howard I.P.(1982) Human Visual Orientation, Wiley, Toronto
Pinker, S. (1997) How the Mind Works. Chapter 4; W.H. Norton, New York.
Howard IP, Bergstrom SS, Ohmi M. (1990) Shape from shading in different frames of reference. Perception 19:523-530.
Howard, I. P. and L. Childerson (1994). The contribution of motion, the visual frame, and visual polarity to sensations of body tilt. Perception 23: 753-762.
Mitelstaedt, H. (1989) Spatial Displays and Spatial Instruments, Ch 42 in: Pictorial Communication in Virtual and Real Environments, Ellis, SR. ed.Taylor & Francis, Lond
Oman, C.M. (1990) Motion sickness: a synthesis and evaluation of the sensory conflict theory, Canadian Journal of Physiology and Pharmacology, 68:294-303, 1990
Oman, C.M., Lichtenberg, B.K. & Money, K.E. Space motion sickness monitoring experiment: Spacelab 1", chapter 12, Motion and Space Sickness, 217-246, Crampton, G.H., ed., CRC Press, Boca Raton, Florida, 1990
Oman, C.M., Lichtenberg, B.K., Money, K.E. & McCoy, R.K. MIT/Canadian vestibular experiments on the Spacelab-1 mission: 4. Space motion sickness: symptoms, stimuli, and predictability", Experimental Brain Research 64:316-334, 1986 [Describes VRIs encountered on STS-9]
Young, L.R., Oman, C.M., Watt, D.G.D., Money, K.E. & Lichtenberg, B.K. "Spatial orientation in weightlessness and readaptation to earth's gravity, Science 225(4658):205-208, AGARD Conference, Istanbul, September,1984
Young, LR, Mendoza, JC, Groleau, N. and Wojcik,
PW (1996) Tactile influences on astronaut visual spatial
orientation: human neurovestibular studies on SLS-2. J.
Appl. Physiol. 81(1):44-49