Optical illusion
Essentially, the ideas of Helmholz, Gregory and Changizi are similar. We do not mechanically turn sense data into a picture of the world, as some had thought. What we do is use our brains to work out what it is we are looking at. This involves the use of memory and logic, though at a fast rate. The process is very good, but not foolproof. When it fails we get an illusion.