Mental Rotation in Left-Right and Mirror-Image Discrimination

Abstract

The orientation effects in left-right (LR) and mirror-image (MI) judgments were examined in four experiments. Experiment 1 directly compared LR and MI judgments. Subjects either decided whether an asterisk appeared on the left or the right side of a rotated letter (LR task) or whether the Letter was in its normal or backwards form (MI task). Estimated rotation rates were slightly faster for the LR task. Experiment 2 measured the effect of the orientation of the previous stimulus on LR and MI judgments. LR or MI judgments were made about a pair of sequential stimuli. The second stimulus could either appear at 0 degrees or at an angle identical to the first stimulus. LR judgments were affected by the orientation of the previous stimulus, but MI judgments were not. Experiment 3 compared the frame of reference employed in LR and MI judgments under headtilt conditions. No difference was found between the reference frames employed in these judgments. Experiment 4 examined whether the transformation rates for LR and MI judgments could be discriminated at the level of subjective strategies that are associated with the mental transformation of the viewer’s own body (kinesthetic) and the mental transformation of objects (kinematic). The transformation rates of these strategies were not different. It was concluded that although orientation effects in LR and MI judgments differed in a number of respects, the differences were task- and stimulus-related, and the underlying transformation process for the two kinds of judgments was actually the same: they both involved mental rotation. Experiment 5 examined the transformation rates for the environmental axes X and Z in an MI task. Consistent with the findings of Experiment 4, no rate difference was found. The results of these experiments were contrasted with those of past studies and were discussed in terms of stimulus and strategy considerations in the measurement of mental rotation rates.