Two abstract shapes appear side by side. Sometimes they’re the same shape rotated to a different angle. Sometimes one is a mirror image of the other. Your brain has to rotate them internally and compare. The bigger the rotation, the harder the task.
The Science: Mental rotation, the seminal spatial cognition experiment (Shepard & Metzler, 1971). Reaction time increases linearly with the angle of rotation — the classic evidence that mental imagery uses spatial computation.
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