Home

About

Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network
FAQHELPSITE MAPCONTACT US


  Advanced Search  

 
1 Introduction Gravity is the most pervasive force that we encounter in our daily lives. Proper orientation
 

Summary: 1 Introduction
Gravity is the most pervasive force that we encounter in our daily lives. Proper orientation
of our bodies with respect to gravity is crucial for balance and motor coordination.
Normally, congruent visual, vestibular (predominantly utricular), and somatosensory
inputs are integrated to obtain a reliable estimate of orientation with respect to the
gravity vector (see Howard 1982, for a review). In some circumstances, such as the
microgravity of space or the artificial worlds of a virtual reality simulation, sensory
information from the otoliths and the visual system can conflict. Discordant visual and
vestibular sensory information has been associated with motion sickness and the similar
nausea that sometimes accompanies a session in a flight simulator (simulator sickness).
The brain uses at least three visual cues in order to make a judgment about the
direction of gravity (Howard and Childerson 1994): visual frame, visual polarity, and
motion of the visual scene. The visual frame refers to sets of distinct horizontal and verti-
cal lines and surfaces. In our environment, these are objects such as walls and ceilings,
which are typically aligned with or perpendicular to gravity. Since the frame is normally
aligned with gravity, tilt of the visual frame suggests a tilt of the gravity vector in the
direction of the tilt of the frame. Perception of the true vertical is more accurate in
the presence of a gravitationally aligned visual frame (Asch and Witkin 1948; Witkin
and Asch 1948a). These authors found that when observers viewed a stationary tilted
frame a vertical rod appeared tilted in the opposite direction. This was interpreted as

  

Source: Allison, Robert - Department of Computer Science, York University (Toronto)

 

Collections: Computer Technologies and Information Sciences; Biology and Medicine