Geometric visual illusions in microgravity during parabolic flight

Abstract

This investigation explores whether the absence of gravitational information in a microgravity environment affects the perception of several classical visual illusions based on the arrangement of horizontal and vertical lines. Because the perception of horizontal and vertical orientation changes in microgravity, our prediction was that the strength of visual illusions based on the arrangement of horizontal and vertical lines would be altered when study participants were free-floating during parabolic flight. The frequency of appearance of reversed-T, Müller-Lyer, Ponzo, and Hering illusions substantially decreased when observers were free-floating, whereas the Zöllner and the Poggendorff illusions were not affected. Because the former illusions rely more heavily on perspective cues for generating inaccurate judgments of depth and size, these results suggest an alteration in the role of linear perspective for three-dimensional vision in microgravity. They also confirm that the visual system normally relies on otolith and somatosensory information for providing accurate judgments about the size and distance of objects when presented with planar presentations of geometric figures.

Balancing awareness: Vestibular signals modulate visual consciousness in the absence of awareness

“…Visual and vestibular information are combined in many centers of the brain in order to allow accurate self-motion perception (Berthoz, Pavard, & Young, 1975;Bremmer, Kubischik, Pekel, Lappe, & Hoffmann, 1999;Siegler, Viaud-Delmon, Israël, & Berthoz, 2000), postural control (Dichgans & Brandt, 1978;Horak, Shupert, Dietz, & Horstmann, 1994) spatial orientation (Clement, Fraysse, & Deguine, 2009;Ferrè, Longo, Fiori, & Haggard, 2013;Villard, Garcia-Moreno, Peter, & Clément, 2005), and have recently also been associated with bodily self-consciousness (Lenggenhager, Smith, & Blanke, 2006;Lopez, Lenggenhager, & Blanke, 2010;Pfeiffer et al, 2013). During self-motion under natural conditions visual and vestibular information are typically congruent, meaning that full-field optic flow on the retina moves in the direction opposite to the movement of the head/body.…”

Mental representation of space in vestibular patients with otolithic or rotatory vertigo

“…The overestimation of the vertical dimension could be because of the anisotropy of the visual field, which is flattish or elliptical in the horizontal direction [18]. However, this theory is in disagreement with the results obtained during parabolic flight showing that the occurrence of geometric illusions decreases in zerogravity, whereas the retinal images are the same [9]. Most likely, gravity is taken as a reference for the judgment of horizontal, vertical, and oblique line directions, which is then used for perception of the perspective.…”

“…In normal participants, a consistent, universal, and unidirectional discrepancy is obtained between judgments of the length or direction of the lines and actual physical measurements of these lines and orientations. In previous studies, we observed that the occurrence of geometric illusions was reduced in patients tilted relative to gravity on the Earth compared with upright [8] or placed in microgravity during parabolic flight [9]. This decrease was presumably because of an influence of the gravitational (otolith) input on the mental representation of the vertical dimension.…”

“…[9]. This noninvasive experiment was performed with good clinical practice as a complementary psychological examination.…”

“…A nonparametric test (Fisher) for comparing the frequency of observations in two unpaired groups (patients vs. healthy participants; OTO vs. ROT) was then applied [9].…”