Postural configuration affects the perception of earth-based space during pitch tilt

Abstract

This study investigates the relative contribution of body parts in the elaboration of a whole-body egocentric attraction phenomenon previously observed during earth-based judgments. This was addressed through a particular earth-based task requiring estimating the possibility of passing under a projected line, imagining a forward horizontal displacement. Different postural configurations were tested, involving whole-body tilt, trunk tilt alone or head tilt alone. Two legs positions relative to the trunk were manipulated. Results showed systematic deviations of the subjective "passability" toward the tilt, linearly related to the tilt magnitude. For each postural configuration, the egocentric influence appeared to be highly dependent on the position of trunk and head axes, whereas the legs position appeared not relevant. When compared to the whole-body tilt condition, tilting the trunk alone consistently reduced the amount of the deviation toward the tilt, whereas tilting the head alone consistently increased it. Our results suggest that several specific effects from multiple body parts can account for the global deviation of the estimates observed during whole-body tilt. Most importantly, we support that the relative contribution of the body segments could mainly depend on a reweighting process, probably based on the reliability of sensory information available for a particular postural set.

To Pass or not to Pass: More a Question of Body Orientation than Visual Cues

“…A comparable linear relationship was subsequently observed when judging objects' elevation and the possibility of passing under them, suggesting that the two estimations shared common processes, intimately linked to the perceived horizontal direction (Bringoux, Robic, Gauthier, & Vercher, 2008). The origin of this body tilt effect observed in darkness upon judgements of passability was recently investigated, demonstrating that several body parts could jointly intervene in this phenomenon (Bourrelly, Bringoux, & Vercher, 2009;Bourrelly, Vercher, & Bringoux, 2011). For instance, we previously highlighted the influence of postural configurations, by manipulating whole-body tilt, trunk tilt alone, and head tilt alone (Bourrelly et al, 2011).…”

“…The present study investigated whether orientational visual cues from optic flow may help to reduce the influence of body tilt previously observed in darkness on estimating the passability under a barrier when imagining a forward horizontal displacement (Bourrelly et al, 2009(Bourrelly et al, , 2011Bringoux et al, 2008). The underlying issues were to better understand how spatial references could interact for the perception of space.…”

“…The origin of this body tilt effect observed in darkness upon judgements of passability was recently investigated, demonstrating that several body parts could jointly intervene in this phenomenon (Bourrelly, Bringoux, & Vercher, 2009;Bourrelly, Vercher, & Bringoux, 2011). For instance, we previously highlighted the influence of postural configurations, by manipulating whole-body tilt, trunk tilt alone, and head tilt alone (Bourrelly et al, 2011). Specifically, when compared to the influence of whole-body orientation, the subjective passability was found to be mainly dependent on the orientation of the head (0.77 cm.deg −1 ) and trunk (0.27 cm.deg −1 ) but not on legs orientation.…”

“…The question arises as to whether visual cuesnamely, those issued from a radial optic flow inducing a forward-horizontal self-motion-may help reduce or even cancel the formerly observed body tilt influence on the subjective passability under obstacles in darkness (Bourrelly et al, 2011;Bringoux et al, 2008). Specifically, if such visual cues provide relevant information congruent with the task requirement (i.e., estimating a horizontal direction), one could expect a reduced influence of body orientation upon subjective passability.…”