Abstract
We explored the effect of gravity on the perceived representation of the absolute distance of objects to the observers within the range from 1.5–6 m. Experiments were performed on board the CNES Airbus Zero-G during parabolic flights eliciting repeated exposures to short periods of microgravity (0 g), hypergravity (1.8 g), and normal gravity (1 g). Two methods for obtaining estimates of perceived egocentric distance were used: verbal reports and visually directed motion toward a memorized visual target. For the latter method, because normal walking is not possible in 0 g, blindfolded subjects translated toward the visual target by pulling on a rope with their arms. The results showed that distance estimates using both verbal reports and blind pulling were significantly different between normal gravity, microgravity, and hypergravity. Compared to the 1 g measurements, the estimates of perceived distance using blind pulling were shorter for all distances in 1.8 g, whereas in 0 g they were longer for distances up to 4 m and shorter for distances beyond. These findings suggest that gravity plays a role in both the sensorimotor system and the perceptual/cognitive system for estimating egocentric distance.
Highlights
Because of its constant presence throughout Earth’s history, terrestrial gravity (1 g) has influenced and shaped life
Testing individuals in altered gravity allows investigating its specific role in biological systems mechanisms such as those involved in visual space perception [1]
Verbal estimates of perceived distance were not significantly different [F (1, 160) = 3.7, p = 0.06] on the road and in the aircraft parked on the runway, so the results were averaged for both conditions
Summary
Because of its constant presence throughout Earth’s history, terrestrial gravity (1 g) has influenced and shaped life. Testing individuals in altered gravity allows investigating its specific role in biological systems mechanisms such as those involved in visual space perception [1]. The visually perceived space refers to a perceptual representation of the immediate physical environment. A major goal of vision research is to characterize the mapping from physical to visual (perceived) space under different conditions of information availability. To reach for an object, we need to know the absolute distance between this object and our body. Visual cues, including binocular disparity, relative motion parallax, angular declination, aerial perspective, linear perspective, and texture gradients, are known to contribute to distance perception [2]. When we move our finger along an object surface, the haptic cues help us to perceive the size and shape of the object, and to determine its distance from our body [3].
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