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.

The perceived offset position of a moving target has been found to be displaced forward, in the direction of motion (Representational Momentum; RM), downward, in the direction of gravity (Representational Gravity; RG), and, recently, further displaced along the horizon implied by the visual context (Representational Horizon; RH). The latter, while still under-explored, offers the prospect to clarify the role of visual contextual cues in spatial orientation and in the perception of dynamic events. As such, the present work sets forth to ascertain the robustness of Representational Horizon across varying types of visual contexts, particularly between interior and exterior scenes, and to clarify up to what degree it reflects a perceptual or response phenomenon. To that end, participants were shown targets, moving along one out of several possible trajectories, overlaid on a randomly chosen background depicting either an interior or exterior scene rotated -22.5º, 0º or 22.5º in relation to the actual vertical. Upon the vanishing of the target, participants were required to indicate its last seen location with a computer mouse. For half the participants, the background vanished with the target while for the remaining it was kept visible until a response was provided. Spatial localizations were subjected to a discrete Fourier decomposition procedure to obtain independent estimates of RM, RG and RH. Outcomes showed that RH’s direction was biased towards the horizon implied by the visual context, but solely for exterior scenes, and irrespective of its presence or absence during the spatial localization response, supporting its perceptual/representational nature.