title: Disambiguation of mental rotation by spatial frames of reference.
abstract: Previous research has shown that our ability to imagine object rotations is limited and associated with spatial reference frames; performance is poor unless the axis of rotation is aligned with the object-intrinsic frame or with the environmental frame. Here, we report an active effect of these reference frames on the process of mental rotation: they can disambiguate object rotations when the axis of rotation is ambiguous. Using novel mental rotation stimuli, in which the rotational axes between pairs of objects can be defined with respect to multiple frames of reference, we demonstrate that the vertical axis is preferentially used for imagined object rotations over the object-intrinsic axis for an efficient minimum rotation. In contrast, the object-intrinsic axis can play a decisive role when the vertical axis is absent as a way of resolving the ambiguity of rotational motion. When interpreted in conjunction with recent advances in the Bayesian framework for motion perception, our results suggest that these spatial frames of reference are incorporated into an internal model of object rotations, thereby shaping our ability to imagine the transformation of an object's spatial structure.
authors.affiliation: Department of Intelligence Science and Technology, Graduate School of Informatics, Kyoto University, Yoshida-Hommachi, Sakyo-Ku, Kyoto, 606-8501, Japan; e-mail:  asakura@cog.ist.i.kyoto-u.ac.jp.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Asakura
authors.forename: Toshio
authors.initials: T
authors.lastname: Inui
keywords: internal model; mental rotation; reference frame