‘What you see isn’t necessarily what you get’ is a good way of summing up the difference between seeing and perception. The eye sees because it responds to varying light input. However, what we perceive is a combination of the sensory input into the eye and what we already know or expect. Anyone who has changed from wearing spectacles with ordinary lenses to those with varifocal lenses is aware of this interaction. With the change of sensory input brought about by varifocal lenses the user has to relearn, to a certain extent, to see things ‘properly’. More extreme cases are evident when individuals who have been blind have their sight restored. They often find it very difficult to ‘see’ because they have not learned how to interpret visual input. In extreme cases they are so distressed, because they cannot ‘make sense’ of what they are ‘seeing’, that they wish they were blind once again. Because perception is not the same as seeing, we can therefore see an incomplete figure, yet percei