Abstract
Exposure to microgravity during spaceflight is known to elicit orientation illusions, errors in sensory localization, postural imbalance, changes in vestibulo-spinal and vestibulo-ocular reflexes, and space motion sickness. The objective of this experiment was to investigate whether an alteration in cognitive visual-spatial processing, such as the perception of distance and size of objects, is also taking place during prolonged exposure to microgravity. Our results show that astronauts on board the International Space Station exhibit biases in the perception of their environment. Objects’ heights and depths were perceived as taller and shallower, respectively, and distances were generally underestimated in orbit compared to Earth. These changes may occur because the perspective cues for depth are less salient in microgravity or the eye-height scaling of size is different when an observer is not standing on the ground. This finding has operational implications for human space exploration missions.
Highlights
Exposure to microgravity during spaceflight is known to elicit orientation illusions, errors in sensory localization, postural imbalance, changes in vestibulo-spinal and vestibulo-ocular reflexes, and space motion sickness [1]
In previous studies we have shown that the occurrence of geometric illusions based on perspective was less frequent in vestibular patients who presented central signs of otolith disorders [9], in healthy observers tilted relative to gravity on Earth [10], as well as in astronauts on board the International
When comparing the dimensions of the cube that the subjects had adjusted so that it looked normal to them, we found no significant difference between the data collected with the astronauts at L-90 days and with the 91 control participants (Figure 1)
Summary
Exposure to microgravity during spaceflight is known to elicit orientation illusions, errors in sensory localization, postural imbalance, changes in vestibulo-spinal and vestibulo-ocular reflexes, and space motion sickness [1]. In an earlier report on two astronauts, we observed that when drawing a Necker’s cube, i.e., a 2D image perceived as a 3D object, the height of the drawing was 9% shorter than its width in zero gravity (0G) [11]. This result suggests that an alteration in the mental representation of space is taking place during exposure to microgravity. Distance perception is the ability for estimating distances between objects in any and all directions relative to an observer’s eye. Depth is looking directly into a hole or tube and estimating forward distances
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