Perception of the upright with tilted and rotating distractors in the fore- and background.

Abstract

To perceive orientation relative to gravity, we combine sensory information with weights proportional to each cue's reliability. However, reliability alone does not fully determine a cue's weight. When asking observers to orient a visual rod parallel to the orientation of gravity in the presence of a static (tilted frame) or dynamic (rotating disc) distractor, some make much larger deviations into the direction of the distractor than others. This idiosyncratic weighting of cues for the perception of verticality has been explained by an individual trait: visual field dependence. However, it can be questioned whether the static and dynamic distractor effects are based on the same mechanism. If they are, changing the depth position of the distractor should induce a similar change in the weighting of static and dynamic visual cues for judging verticality. To test this, we placed the distractors at a different depth than the rod and reversed their depth order while keeping their retinal extent constant. This change influenced the two distractor effects differently: the effect of the disc was considerably larger when it was in the background, whereas the effect of the frame reduced. Furthermore, the effect of depth order did not show a significant correlation between the two distractors. Our findings thus suggest that static and dynamic distractor effects are based on at least partly different mechanisms, implying that there is not a single visual dependence.