The human brain has phenomenal power in its ability to understand written language even when letters are out of order, as long as the first and last letters are in the right place. The brain does not read each letter individually but perceives words as a whole. Various optical illusions demonstrate how the brain can perceive images that are not really present or can be tricked into seeing motion where there is none. Some illusions appear to show that different people may use different hemispheres of the brain for certain tasks like determining the direction of rotation for an image.