title: Long-Duration Spaceflight Increases Depth Ambiguity of Reversible Perspective Figures.
abstract: The objective of this study was to investigate depth perception in astronauts during and after spaceflight by studying their sensitivity to reversible perspective figures in which two-dimensional images could elicit two possible depth representations. Other ambiguous figures that did not give rise to a perception of illusory depth were used as controls. Six astronauts and 14 subjects were tested in the laboratory during three sessions for evaluating the variability of their responses in normal gravity. The six astronauts were then tested during four sessions while on board the International Space Station for 5-6 months. They were finally tested immediately after return to Earth and up to one week later. The reaction time decreased throughout the sessions, thus indicating a learning effect. However, the time to first percept reversal and the number of reversals were not different in orbit and after the flight compared to before the flight. On Earth, when watching depth-ambiguous perspective figures, all subjects reported seeing one three-dimensional interpretation more often than the other, i.e. a ratio of about 70-30%. In weightlessness this asymmetry gradually disappeared and after 3 months in orbit both interpretations were seen for the same duration. These results indicate that the perception of "illusory" depth is altered in astronauts during spaceflight. This increased depth ambiguity is attributed to the lack of the gravitational reference and the eye-ground elevation for interpreting perspective depth cues.
authors.affiliation: Lyon Neuroscience Research Center, Bron, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Clément
authors.affiliation: Pennsylvania State University, University Park, Pennsylvania, United States of America.
authors.forename: Heather C M
authors.initials: HC
authors.lastname: Allaway
authors.affiliation: International Space University, Strasbourg, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Demel
authors.affiliation: International Space University, Strasbourg, France.
authors.forename: Adrianos
authors.initials: A
authors.lastname: Golemis
authors.affiliation: McGill University, Montreal, Canada.
authors.forename: Alexandra N
authors.initials: AN
authors.lastname: Kindrat
authors.affiliation: Western University, London, Ontario, Canada.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Melinyshyn
authors.affiliation: OrbitOne Consulting, Calgary, Canada.
authors.forename: Tahir
authors.initials: T
authors.lastname: Merali
authors.affiliation: University of Calgary, Calgary, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Thirsk
mesh_terms: D000328:Adult; D018480:Astronauts; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009949:Orientation / Q000502:physiology; D010775:Photic Stimulation; D013026:Space Flight; D055815:Young Adult