Dissociating viewpoint costs in mental rotation and object recognition

Abstract

In mental rotation, participants must determine whether two stimuli match when one undergoes a rotation in 3D space relative to the other. The key evidence for mental rotation is the finding of a linear increase in response times as objects are rotated further apart. This signature increase in response times is also found in recognition of rotated objects, which has led many theorists to postulate mental rotation as a key transformational procedure in object recognition. A number of recent studies, however, have reported inconsistencies between performance on mental rotation and object recognition tasks. These results led us to reexamine the similarity of viewpoint costs in mental rotation and object recognition. Following Gauthier et al. (2002), we conducted tasks which were identical except that mental rotation required a judgment of object handedness (whether it was mirror-reflected before rotation) whereas object recognition required an identity judgment. In each task, two stimuli were shown in succession, and might be rotated in depth by up to 165°. Mental rotation costs increased linearly with rotation, but object recognition costs increased only over small rotations, and then were reduced as rotations approached 165°. These results show that viewpoint costs can be dissociated between mental rotation and object recognition. When taken in conjunction with the brain-imaging results of Gauthier et al. (2002), our results suggest that whereas mental rotation requires internal 3-D rotations, object recognition requires feature matching of view-specific representations.