Are you absolutely certain that what you see is what is really there? Actually, the world you see is not necessarily the actual world in front of you. In other words, what you are seeing is not the world as it really is. The brain function of ‘seeing’ is rather subjective. In part this is because each eye really does have a ‘blind spot.’ There is no retina at the point opposite the pupil of your eye where the fibers of the optic nerve bunch together. This means there is no ‘seeing’ at this spot on the retina. Most people do not notice this because the brain tends to fill in what you cannot see. This natural phenomenon is believed to contribute to your brain’s perception of both optical illusions and trompe l’oeil—believed to reflect slightly different types of human visual perception. How do optical illusions and trompe l'oeil differ? More tomorrow.