Consider, first, that all your five senses are differing forms of one basic sense—something like touch. Seeing is highly sensitive touching. The eyes touch, or feel, light waves and so enable us to touch things out of reach of our hands. Similarly, the ears touch sound waves in the air, and the nose tiny particles of dust and gas. But the complex patterns and chains of neurons which constitute these senses are composed of neuron units which are capable of changing between just two states: on or off.
