Mental rotation is the cognitive act of rotating a mental representation of an object—imagining how it would look from a different angle, or comparing two shapes to determine whether they are the same or mirror images. The classic study (Shepard & Metzler, 1971) showed that reaction time to compare two 3D shapes increases linearly with the angle of rotation, suggesting people perform an analog mental transformation.
Mental rotation is a spatial reasoning ability, related to but distinct from visual imagery vividness. Some people with aphantasia perform normally on mental rotation tasks despite reporting no internal pictures—suggesting that spatial representation and conscious visual experience are partly separable systems. Mental rotation is widely used in cognitive psychology and STEM education research, and is often tested separately from imagery questionnaires like the VVIQ. Imagination Index does not measure mental rotation directly but covers visual imagery vividness across multiple subcategories.