Mental rotation of compound stimuli: the effects of task demands, practice, and figural goodness.

Four experiments examined whether or not mental rotation of compound stimuli is a holistic process. Large letters (global aspect) composed of small letters (local aspect) were presented, and the format (normal vs. reflected) of each aspect was manipulated independently. In Experiment 1, the rate of mental rotation was compared under divided- and focused-attention instructions. The overall rate of mental rotation was faster under focused-attention instructions than under divided-attention instructions. Also, contrary to previous findings, in the divided-attention task, the slope of the rotation function was smaller when the stimulus configurations contained aspects with congruent formats (both aspects were normal or mirror-reversed letters) than when they contained aspects with incongruent formats (one normal and one mirror-reversed letter). This pattern of results is unlikely to be caused by the subjects' level of familiarity with the divided-attention task (Experiment 2), by postrotation processes (Experiment 3), or by stimulus attributes (figural goodness) confounded with the format-congruency variable (Experiment 4). The implications of these results for models of mental rotation of compound stimuli are discussed.