Visual Orientation in Unifamiliar Gravito-Intertial Environments
Principal Investigator: Charles M. Oman, Ph.D.
PROJECT OVERVIEW
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 ?
Our understanding of the underlying physiology - for example
how the human sense of direction is neurally coded in weightlessness
- is incomplete. We will experimentally determine what visual
cues are critical for orientation, navigation, visual search
and 3D spatial memory in "agravic" visual environments,
study underlying neural mechanisms in an animal head direction
cell model in 1-G and parabolic flight, and develop a prototype
VR based space station visual orientation trainer. Five different
studies are underway:
|
Visual Orientation in Static Real Environments (Dr. Howard) |
|
Visual Search & Spatial Memory Training (Drs. Shebilske and Oman) |
|
Visual Orientation in Virtual Environments (Drs. Shebilske, Oman, and Beall) |
|
Rat Head Direction Cell Model for Visual Orientation in altered G. (Drs. Taube and Oman) |
|
Space Station Visual Orientation Trainer (Drs. Oman and Beall) |
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.
Supine
subjects looking at visual scene through a 45 deg. tilted mirror
.
Subjects often feel as if they are standing erect.
TAMU Visual Search and Spatial Memory
Experiment (Click on this picture to view and enlarged
version).
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.
Prototype
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
INTRODUCTORY BOOKS
Howard I.P.(1982) Human Visual Orientation, Wiley, Toronto
Pinker, S. (1997) How the Mind Works. Chapter 4; W.H. Norton, New York.
Cooper, H.S. (1976) A House In Space, Holt, Rinehart & Winston, New York. [First description of visual illusions encountered in space stations]
JOURNAL ARTICLES
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