Aphantasia is the inability to voluntarily imagine vivid imagery in your mind's eye. It is estimated that ~2% of the population have aphantasia cannot imagine any visual imagery in this way. However, each person has a different level of visualization ability ranging seeing nothing in their mind's eye to being able not only to produce extremely vivid mental images but – at its extreme – also being able to superimpose imagined objects into their visual field almost indistinguishable from reality.