Astronauts have reported episodes of disorientation relatively frequently in
microgravity and on return to Earth. Such episodes have the
potential to interfere with an astronaut's performance and
to jeopardize safety. The OVAR Laboratory is primarily concerned
with understanding the mechanisms by which judgments of orientation
are made in order to understand the causes of the episodes
of disorientation and hopefully to provide ways of eliminating
such episodes. The laboratory uses oculomotor and perceptual
tasks to measure where astronauts feel themselves to be in
three-dimensional space and in which direction they are moving
or facing. This subjective location is called the egocenter
and its location and direction is determined by both otolith
and somatosensory inputs. Experiments on Earth which modify
these inputs alter people's judgments of where they are and
which direction they are facing. Vestibular disorders affect
orientation perception and it seems that, corresponding with
the recovery process, over time the balance  between vestibular and somatosensory input in determining
orientation is altered. It is anticipated that similar changes
will take place during prolonged microgravity and then again
another re-balancing between vestibular and somatosensory
input will occur on return to a 1-g environment. This laboratory
is the only laboratory that has initiated a direct investigation
of the changes in the straight-ahead direction in astronauts.
We measure the subjective straight-ahead by psychophysical tests requiring verbal
responses and oculomotor responses. In a typical psychophysical
test the subjects is asked to indicate when a spot crosses
their perceived straight-ahead or to return the gaze to the
straight-ahead position from various off-center positions.
In a typical oculomotor task the subject will be required
to look straight ahead during a period of darkness in order
to determine where gaze shifts, and eye position will be
measured using videooculography.
Image right: Off Vertical
Rotation - Measurement of Perception and Video Recording
of Eye Movements
The Off-Vertical Axis Rotator allows
investigators to study eye movements and motion perception
while continuously changing the orientation of the subject
relative to gravity. This device is currently being used
to examine adaptive changes in otolith-mediated responses
following short-duration Shuttle flights (DSO 499), as well
as examining vestibular-autonomic interactions.
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