References
- Gregory , R. L. 1970 . The Intelligent Eye , London : Weidenfeld and Nicholson .
- Gregory , R. L. 1971 . Multistability and perception . Scientific American , December : 63 – 71 .
- Gregory , R. L. 1978 . Eye and Brain—the Psychology of Seeing , 3rd edn , London : Weidenfeld and Nicholson .
- Ittleson , W. H. 1952 . The Ames Demonstrations in Perception , London : Oxford University Press .
- Penrose , L. S. and Penrose , R. 1958 . Impossible objects: a special type of illusion . British Journal of Psychology , 49 : 31