Effects of supine body position and low radial accelerations on the visually perceived apparent zenith

Effect of low gravitational stimulation on the perception of target elevation: Role of spatial expertise

“…Basically, we replicated the experiments of Raphel and Barraud (1994;VPEL) and Raphel et al (2001;VPAZ).The VPEL experiment was conducted under five experimental conditions corresponding to five angular velocities: 0 (motionless), 10, 20, 50, and 105º/sec. The VPAZ experiment was conducted under six experimental conditions corresponding to the angular velocities of 0º (motionless), 60º, 80º, 100º, 120º, and 140º/sec.…”

“…Moreover, the perception of the eye level corresponded to a logarithmic psychophysical function, but the theoretical thresholds of sensitivity to radial accelerations were different from those already described in the literature for similar experimental conditions. The theoretical threshold-that is, the radial acceleration of centrifugation observed when the deviation of the subjective reference was null (i.e., γ r for dγ r ϭ 0)-was higher in the upright position (0.02 m/sec 2 vs. 0.0006 m/sec 2 ; Raphel & Barraud, 1994) whereas it was lower in the supine position (0.11 m/sec 2 vs. 0.38 m/sec 2 ; Raphel et al, 2001). These differences could be connected to the interindividual variability, which is the main purpose of the present work.…”

“…In the range of very low gravitational-inertial stimulation, errors were also reported in the perceived elevation of a visual target that is viewed by an observer in a supine position (Raphel, Cian, Barraud, & Micheyl, 2001). When the body and head axes are perpendicular to the direction of gravity (i.e., in the supine position), the subjective perception of the eye level corresponds to the plane as being parallel to the direction of gravity (visually perceived apparent zenith: VPAZ).…”

“…This difference may be related to a difference in sense organ stimulation. Considering the spatial position of the otolithic system-that is, the orientation of the utricular membrane close to the horizontal plane when the head is held erect whereas the saccular maculae is oriented globally nearly vertically (Citek & Ebenholtz, 1996;Curthoys et al, 1999;Kelly, 1991)-and the shearing force acting on it, it has been assumed that the utricular membrane is involved in the eye level lowering in the upright position (Raphel & Barraud, 1994) and in the saccular maculae in the supine position (Raphel et al, 2001). Within an ecological framework of sensory signals processing, the relevance and the processing of the utricular and saccular signals may depend on the conditions under which these sensory organs are usually stimulated.…”

“…The principal aim of this study was to understand how the relation that the subject maintains with the spatial environment-that is, the knowledge acquired through accumulated experience-modifies the processing of sensory information and the perceptive construction resulting from it. To achieve this goal, we replicated the experiments of Raphel and Barraud (1994) and Raphel et al (2001)-that is, their studies of low gravitational-inertial stimulation applied to subjects in the upright and in the supine positions, respectively-with two different populations: (1) subjects without sports expertise and (2) highlevel acrobats (trampolinists). More precisely, we investigated to which extent the spatial expertise modifies the influence of low gravitational-inertial disturbances on the eye level.…”