Regularity of Symmetry Verticality Guides Perceptual Judgments of Objects

Abstract

Previous research indicated that most salient, real-world objects possess natural regularities that observers commonly assume in perceptual judgments of figural orientation and interpretation. Regularities include 3-dimensionality, bilateral symmetry, and the tendency for object tops to possess more salient information than bottoms. Thus, when observers interpret randomly shaped figures, they reliably impose volume, bilateral symmetry, and top and front orientation directions, even when figures are 2-dimensional and asymmetric. We confirmed generalizability for observers to assume these regularities with stimuli that vary in complexity, and we found evidence supporting another regularity, that of symmetry verticality (symmetry about a vertical axis). Findings support use of a family of perceptual heuristics corresponding to natural regularities that constrain stimulus indeterminacy and help guide judgment of object orientation and interpretation.

Shape, Gravity, and the Perception of the Right Angle

“…Thus, when rotated, Mach's square becomes a diamond, a form whose figural axis, like the page vertical, bisects two of its angles. Schiano et al (2008) have similarly demonstrated that observers tend to impose bilateral symmetry on 2-D figures interpreted as having 3-D volume, and that the axis of perceived symmetry is preferentially selected to correspond with the frame/visual field vertical (the two coincide in this study). This`attraction' of the figural axis to the frame vertical accounts for the observation that symmetry around the frame vertical is more easily perceived than symmetry around the horizontal (Goldmeier 1972).…”

“…According to Attneave, it possesses a``vertical-like quality'', while Rock and Leaman refer to it as the figure's``phenomenal vertical''. Rock and Leaman (1963) and Schiano et al (2008) also demonstrate that the perceived`top' and bottom' of a form tend to be perceived as lying along this axis.…”

The Perception of Symmetry in Depth: Effect of Symmetry Plane Orientation

“…Observers were better at discriminating symmetric and asymmetric depth when this plane was vertical-the y-z plane-than other orientations tested, either the horizontal x-z plane or oblique planes with intermediate orientations. A preference for 3-D symmetry about the vertical is also found when observers give interpretations to random 2-D figures [35]. The frontoparallel symmetry of the stimuli used in the study-that is, the symmetry of the disks' x-y values-is not implicated in this, for the advantage was specific to the even depth symmetry tested in Experiment 1 and did not appear for discrimination of depth repetition or depth gradients, despite the frontoparallel symmetry of all the stimuli.…”

Children and adults exhibit a common vertical attention bias for object tops and scene bottoms.

“…The upper portion of objects tends to be more visible than the lower part resting on the ground, and in the case of animals, their heads and the parts of their bodies that most clearly indicate intentionality are typically near their top. Other natural regularities are present, with most organisms and other objects of interest displaying 3D symmetry and orientations that are generally vertically upright (McBeath et al, 1997; Schiano et al, 2008). Motion patterns exhibit natural regularities like tendencies for forward-facing and axis-aligned motion, especially the motion patterns associated with living organisms and human artifacts (Dolgov et al, 2009; McBeath, et al, 1992), and it follows that observers exhibit a bias to attend to these nonarbitrary more meaningful motion patterns (Wallis & Bulthoff, 2000).…”