Perception of Egocentric Distance during Gravitational Changes in Parabolic Flight

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.

Horizontal and Vertical Distance Perception in Altered Gravity

“…www.nature.com/scientificreports www.nature.com/scientificreports/ Horizontal distance judgments were symmetrical in 1 g, and changes in the gravity level did not alter this symmetry during either blind pulling or verbal reporting. However, overall horizontal distance judgments were underestimated in 0 g compared to 1 g. This result is in agreement with our previous study where sitting subjects judged the distance of targets presented straight-ahead and were blind pulling in the forward direction 15 . In this previous study, distances were also underestimated in 0 g compared to 1 g during blind pulling, and to a lesser degree in verbal reports.…”

“…The rail was attached to the aircraft's seat tracks, along the x-direction of the aircraft, using supporting beams and nut fittings. The subjects moved along the rail by pulling on a rope that was tensioned with turnbuckles to vertical beams attached at both ends of the rail above the subjects' head 15 . For horizontal distance judgments, the subjects were seated upright and translated sideways to the right or left (Fig.…”

“…At no point during the test did the subjects receive a feedback on their distance estimate performance. Two video cameras recorded the experiment in its entirety 15 .…”

“…The fact that it is forbidden for test subjects to walk during the 1.8 g pull-ups and pull-outs of parabolic flights for safety reasons coupled with the impossibility for subjects to walk during in 0 g (their feet don't contact the floor in free-fall) drove our decision to use blind pulling. Previous experiments have shown that the responses from blind pulling correlate strongly with those of blind walking 14,15 . Both blind pulling and blind walking are open-loop processes based on one initial visual input that the brain processes to estimate the distance to be traveled.…”

Modality-independent effect of gravity in shaping the internal representation of 3D space

“…For example, tilting the body with respect to gravity affects objects recognition (Leone 1998, Barnett-Cowan et al 2015, orientation and distance perception (Marendaz et al 1993, Harris andMander 2014) and other phenomena as the tilted frame illusion (Goodenough et al 1981, Howard 1982, the oblique effect (Lipshits and McIntyre 1999, Luyat and Gentaz 2002, McIntyre and Lipshits 2008 and some geometric illusions (Prinzmetal andBeck 2001, Clément andEckardt 2005). Furthermore, weightlessness significantly alters the perception of stimulus size and shape, especially in tasks involving depth, during both short-term (Villard et al 2005, Clément and Bukley 2008, Harris et al 2010, Clément and Demel 2012, Clément et al 2016, Bourrelly et al 2016) and long-term , De Saedeleer et al 2013, Bourrelly et al 2015 exposure. One hypothesis to explain gravity-related changes in visual perception is that gravity affects both the eye movements underlying visual exploration (Clément et al 1986, Reschke et al 2017 and eye positioning that contribute to the estimation of the visual eye-height, a key reference within the visual scene (Goltz et al 1997, Bourrelly et al 2016).…”