The simplest way to describe an optical illusion is that it is a ‘trick’ that our eyes play on us. We seem to
see something that isn’t really so. Or we may be able to see the same object in two completely different
ways. If our eyes are working properly, and they are instructions for seeing exactly what is before
us, how can they play such tricks on us? This is because vision is not a physical process. It is not like
photography, for instance, which work mechanically. Vision is really a psychological experience, because
it is not the eyes that see, but our brain.