Long-Duration Spaceflight Increases Depth Ambiguity of Reversible Perspective Figures.
Bottom Line: 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.These results indicate that the perception of "illusory" depth is altered in astronauts during spaceflight.
Affiliation: Lyon Neuroscience Research Center, Bron, France.
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.
No MeSH data available.
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Mentions: The percentage of time for seeing each interpretation was not significantly different between the control subjects and the astronauts for both the silhouettes [F (1,119) = 2.52, p = 0.115] and the perspective figures [F (1,239) = 0.855, p = 0.356]. However, there was a clear difference in the duration for seeing each interpretation between the silhouettes and the perspective figures for both the control subjects [F (1,251) = 66.8, p < 0.001] and the astronauts [F (1,107) = 65.2, p < 0.001]. When averaged across all 20 subjects the mean percentage of time for seeing the old woman and the golfer in the silhouettes was 50.5% (SD 11.9), i.e. close to chance. However, there was a 67%-33% asymmetry for seeing the perspective figures. The interpretations corresponding to the low inserts in Fig 1 were the most often seen. The mean percentage of time for seeing the Necker cube from above was 63.2% (SD 12.0%), the structure center popping out 65.8% (SD 12.3%), the large parallelograms in the foreground 66.8% (SD 14.3%), and the chair seat pointing toward the observer 71.2% (SD 14.3%). The interpretations that were seen for the longest duration were also the first interpretations that were seen on each trial (r2 = 0.74). Repeated measures ANOVA yielded no significant difference in the duration for seeing each interpretation across the 3 pre-flight sessions and the 6 figures for the control subjects, but a significant difference across the perspective figures for the astronauts [F (3,71) = 4.96, p = 0.004] (Fig 7).
No MeSH data available.