Object's symmetry alters spatial perspective-taking processes.

Spatial perspective-taking (SPT) refers to one's ability to identify or understand the location of a target relative to another viewpoint, which could be specified by a human-like agent or a reference object (e.g., a chair). Previous studies have shown that SPT is characterized by different processes depending on whether one is required to make a left/right or front/behind judgment. An object's shape, however, may also account for the different processes, as previous studies typically used reference objects that were left-right symmetrical and front-back asymmetrical (e.g., human figures, dolls, or chairs), thus confounding effects of judgment direction and effects of objects' shape. To address this issue, we manipulated objects' shape (symmetrical or asymmetrical about front-back or left-right) independently of judgment direction (i.e., left/right or front/behind) and compared participants' efficacy of such judgments. Our results showed that egocentric transformations were used more frequently for judgments orthogonal to the object's symmetry plane than for judgments orthogonal to the object's asymmetry plane, whereas the inverse was true for mental scanning. Notably, these tendencies were observed regardless of whether the judgment was about left/right or front/behind. Nonetheless, egocentric transformations were found to be more difficult to apply to the front/behind judgments than to the left/right judgments. We also found that this difficulty was alleviated by rich imagination. Furthermore, we found that participants tended to erroneously perceive a front-back symmetrical human-like object as facing them, even when it was actually facing away from them (facing bias). This in turn forced the participants to conduct unnecessary egocentric transformations. Overall, our findings demonstrated that objects' symmetry dramatically influenced SPT processes.