We can measure the angular velocity of mental objects, and it appears to increase linearly with the degree of rotation relative to a reference. See Shepard, R.

We can measure the angular velocity of mental objects, and it appears to increase linearly with the degree of rotation relative to a reference. See Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171(3972), 701–703. https://psycnet.apa.org/record/1971-28060-001 https://psycnet.apa.org/record/1971-28060-001