The document presents a study investigating the perceptual reversal of bi-stable ambiguous figures in different gravitational environments, specifically upright and supine positions. The research, conducted by a team including professionals from various institutions, aimed to determine how gravity influences the perception of these figures through a series of trials with volunteers. Results indicated that subjects experienced fewer perceptual shifts when supine, highlighting the central nervous system's reliance on gravitational cues for interpreting 3D information.

1. Perceptual Reversal of Bi-Stable Ambiguous Figures
Bi Stable
in the Upright and Supine Positions
Sonny Kohli, MD FRCPC (Internal Medicine, Critical Care), Flight Surgery, ISU SSP 2008
on behalf of the IRIS team investigators: Dawn Lim, Michael Demel, and Gilles Clément
Nov 21, 2009
CSS Summit
Kingston, Ontario

2. Perceptual Reversal of Bi-Stable Ambiguous Figures
in the Upright and Supine Positions
Dawn Lim, University of Toronto, Division of Emergency Medicine, Toronto, Canada
Michael Demel, International Space University, Strasbourg, France
Sonny Kohli, Oakville Trafalgar Memorial Hospital, ISUSSP 2008 Alumnus
Gilles Clément, Centre National de la Recherche Scientifique, Toulouse, France

3. Ambiguous Figures
• Perceptual Instability
• evoked by binocular rivalry
• evoked by ambiguous figures
• Perceptual Reversal
• transitions from one percept to its alternative
• (Bi St bl ) Ambiguous Fi
(Bi-Stable) A bi Figures
• are bi-stable because in the real world they could potentially
exist in one of two different configurations
• are not true illusions because no false perception occurs
• allow for more than one perceptual interpretation, each of
which is accurate
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 3

4. “Iris” Experiment
Iris
• International Space University (ISU) Life Science Project
p y( ) j
• Objective:
j
• investigate whether perception (of perspective-reversible figures)
is altered by gravity
Environments:
E i
• 1 g – supine versus upright (ie tilted to gravity)
• 0 g - parabolic flight (ESA 50th Parabolic Flight Campaign)
• Micro g orbital flight (ISS Increments 19/20)
g-
• Supported by CSA, CNRS, UTSI, CNES, ESA, NASA
pp y , , , , ,
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 4

5. Iris Software
• Series of 10 perspective reversible figures
• Each figure displayed for 60 seconds
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 5

7. 3

9. Method
• Test subject inclusion criteria
• between 18-60 years of age
18 60
• no uncorrectable ocular-vestibular pathology
• ability to concentrate on a computer screen for approximately
ten minutes at a time
• able t commit to completing all three coupled trials over a
bl to it t l ti ll th l dt i l
two-week period
• 14 volunteers
• 8 males, 6 females
l f l
• aged 28-36 years (mean: 32.2 years)
• normal or corrected-to-normal visual acuity
• Studies performed in accordance with the ethical
d f d d h h h l
standards laid down in the Declaration of Helsinki
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 9

10. Conditions
Upright Supine
Photo Credit: D. Lim
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 10

11. Procedure
• Three coupled trials spaced one week apart
• 7 subjects randomly chosen to be tested in upright p
j y p g position first
for each coupled trial
• remaining 7 subjects to be tested in supine position first for each
coupled trial
• randomization used to counterbalance for any possible learning
a do a o u d o ou ba a o a y po b a g
effects gained with the repetition of the experiment
• For each trial:
• presentation of all 10 figures in each of the upright and supine
positions
• test subjects were allowed to rest their eyes as needed in between
each figure.
• For
F each figure:
h fi
• user was prompted to specify via predefined keystrokes ('F' or 'J')
which percept he or she visualized first, then every subsequent
change in perception until 60 seconds passed
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 11

12. Data Analysis
• Measurements:
• the time for the first percept, i.e., the time from stimulus
onset to the first percept report
• the first percept seen ('F' or 'J’)
• the time from the first percept report to the first perceptual
h f h f h f l
reversal
• the mean duration of perceptual reversals
• Perceptual reversal rate:
• calculated as the time from the first percept report to the end
of the trial divided by the mean percept duration
12/12/2009 Perceptual Reversal of Bi-Stable Ambiguous Figures in the Upright and Supine Positions 12

13. Results—Effect of Trials
p < 0.05
p < 0.05
p < 0.05

14. Results—Effect of Body Position
p < 0.05

15. Conclusions
• when supine, subjects shift perspectives less frequently
• gravitational cues are used by the CNS for interpretation of
ambiguous figures
• the decrease in perceptual instability when supine confirms
the importance of a gravitational reference in 3 D
3-D
information processing
• these observations emphasize the role of the vestibular
(otolith) system and a gravitational reference for 3D
p
perception
p

16. Strengths
• Simple study design
• Student driven process is novel
• Easily reproducible in multiple environments: Zero gravity
and Microgravity
Limitations
• Should be performed in micro- and zero-gravity
• Do our findings apply to more complex, realistic tasks?

17. Thank you for your attention
attention.
Figure Credits (Slide 4):
Fi C dit (Slid 4)
(A) E. Mach; (B) L. A. Necker; (C) J.-M. Hupé; (D) L. Fagerlie; (E) G. Clément; (F) N.
Kayahara; (G) unkown; (H) NASA; (I) Y. Bonneh; (J) M. C. Escher