Michaelsen, E.E.MichaelsenMeidow, J.J.Meidow2022-03-062022-03-062019https://publica.fraunhofer.de/handle/publica/26654410.1007/978-3-030-04040-6_72-s2.0-85060179654For the time being, this chapter is quite short. We are not aware of any elaborated theory of illusion. After a short review about what has been proposed in the literature, our main idea is presented, i.e., deriving illusion from top-down search procedures. A competing alternative approach emanates from the main function of illusion, i.e., a means to counter occlusion.en004670book article