Mental rotation with egocentric and object-based transformations.

Two experiments were conducted to address methodological issues with past studies investigating the influence of egocentric and object-based transformations on performance and sex differences in mental rotation. In previous work, the egocentric and object-based mental rotation tasks confounded the stimulus type (embodied vs. non-embodied) and transformation task (egocentric vs. object-based). In both experiments presented here, the same stimuli were used regardless of the type of transformation but task instructions were modified to induce either egocentric (left-right judgment) or object-based (same-different judgment) processing. Experiment 1 used pairs of letters whereas Experiment 2 presented pairs of line-drawings of human hands. For both experiments, it was hypothesized that the mental rotation slope for response time would be steeper for object-based than for egocentric transformations. This hypothesis was verified in both experiments. Furthermore, Experiment 2 showed a reduced male advantage for egocentric compared to object-based rotations, whereas this pattern was reversed for Experiment 1. In conclusion, the present study showed that the influence of the type of transformation involved in mental rotation can be examined with the same set of stimuli simply by modifying task instructions.