Turning shapes inside your head
Deciding if a turned shape is the same shape takes longer the further it is turned, as if you rotate it in your mind at a steady speed.
You form a picture of the shape in your head.
You turn that picture smoothly, and bigger turns take measurably longer.
That inner turning is spatial thinking: maps, mirrors, geometry, parking.
Then and now
The 1971 chronometry held up: scanners later watched the parietal cortex doing the turning the reaction times predicted.
Shepard, R. N. and Metzler, J. (1971)
Where it began“Mental rotation of three-dimensional objects”
Science, 171, 701-703
Time to judge rotated objects rises linearly with the rotation angle: evidence of genuine mental rotation.
Zacks, J. M. (2008)
State of the art“Neuroimaging studies of mental rotation: A meta-analysis and review”
Journal of Cognitive Neuroscience, 20(1), 1-19
Brain imaging confirms it: mental rotation engages parietal circuits and behaves like a genuinely analog inner rotation.
What we do and do not claim
Rotation speed improves with practice in the task. We show that improvement, and only that.