You don't have to poke yourself in the eye or do anything gruesome or painful.
In one of his marvellous books, Richard Dawkins explains how the brain makes a difference between the two different ways of looking to one side (say your left): (a) turning your head and (b) swivelling your eyes while keeping your head still. In both cases, of course, the scene in front of you sweeps across the retina. In the first case the brain allows this and the scene moves rapidly to the right as it would in a pan from a movie camera. In the second case the brain keeps the scene still while your eyes move across it. (cont)