Visual space orientation and representational gravity: Contextual orientation visual cues modulate the perceptual extrapolation of motion.

Abstract

The perceived offset of a moving target is usually displaced forward, in the direction of motion (representational momentum), and downward, in the direction of gravity (representational gravity). In what refers to the latter, the meaning of "downward in the direction of gravity" is ill-defined, for it is known that the perceived direction of gravity ("downward") results from the interaction of vestibular signals, sensitive to the gravito-inertial vector, an aprioristic tendency to assume that it aligns with the body's main axis (idiotropic vector) and visual cues. The present work aims to disclose what effects visual cues have on representational gravity. Participants performed a spatial localization task as well as a subjective visual vertical (SVV) and an oriented character recognition task (OCHART), with stimuli superimposed on a realistic background either aligned with earth's vertical or tilted rightward or leftward. Outcomes disclosed significant and lawful effects of the orientation of the visual context on spatial localization judgements. Specifically, forward displacement along the target's motion direction was bigger for targets moving along the "horizontal" direction implied by the background scene. These trends were furthermore found to be correlated, at an individual level, with the magnitude of SVV, but not with the perceptual upright (as measured with OCHART). These findings show that features of the spatial localization judgements specifically index the visually induced spatial orientation, thus offering the prospect to expand available tools for inquiries concerning human spatial orientation, besides clarifying the multisensorial nature and significantly expanding the notion of representational gravity. Public Significance StatementThis study reveals that the orientation of the visual context affects the spatial localization of moving targets, in accordance with the hypothesized role of an internal model of gravity. The found outcomes, besides adding to the current knowledge on the visual representation of gravity and human spatial orientation, offer tentative prospects for clinical assessment tools and human factors insights.

Representational horizon and visual space orientation: An investigation into the role of visual contextual cues on spatial mislocalisations

“…The coefficient a 2 is typically found to be significant, reflecting an increase in forward displacement for horizontally moving targets-Representational Horizon. Importantly, it has been previously reported (Freitas & De Sá Teixeira, 2021) that the orientation of the visual context is accompanied by a modulation of coefficient b 2 such that the orientation of Representational Horizon is biased toward the horizon implied by the visual context (see Fig. 3, third inset line).…”

“…In this vein, the present study has as its primary objective to replicate the results of Freitas and De Sá Teixeira (2021), specifically in what refers to the effect of visual context orientation on the second harmonic present in M-displacements-which we coin Representational Horizon-and to extend that finding for a variety of scenes, beyond the one used in that previous study. As a secondary goal, we set forth to ascertain to what degree Representational Horizon is determined by the presence of the visual context during the spatial localisation response or if it only requires that the inducing moving stimuli is shown embedded in it.…”

“…Coefficients a 1 and b 1 , taken together, reflect an increased displacement towards one preferred direction; in previous studies (De Sá Teixeira, 2016b;Freitas & De Sá Teixeira, 2021), a 1 was found to be null and a negative b 1 is commonly found, which translates as a greater displacement downward, towards the participants' feet and, thus, taken as a measure of Representational Gravity (see Fig. 3, second inset line).…”

“…Based on the reported magnitude of the effect of visual context orientation (partial η 2 = 0.21, for the coefficient b 2 ) in Freitas and De Sá Teixeira ( 2021 ), a power analysis reveals that a minimum sample size of 12 participants would be required. To strengthen the robustness of statistical inference, forty participants (29 females; 11 males) were recruited for the experiment in exchange for partial course credits.…”

“…The relevance of this latter harmonic component has only recently been ascertained, though. Freitas and De Sá Teixeira ( 2021 ) conducted a study where M-displacement was measured for targets moving along 16 possible directions (leftward, rightward, downward, upward, and varying degrees of diagonal trajectories in between) while overlaid on a background image depicting the interior view of the Harmony module of the International Space Station, which could be either on an upright orientation or tilted leftwards or rightwards by 22.5º. The second harmonic’s orientation was found to be biased towards the horizon implied by the visual context—that is, targets moving along the horizontal line implied by the background scene (irrespective of its misalignment with the actual horizontal) led to increased M-displacements.…”