There are four main mechanisms involved in processing and learning a physical skill: input received via the senses, information processing in the brain, output produced by the muscles, and feedback. Individual ability to learn depends on factors like physical maturation, fitness, attention, motivation, feedback, memory, amount and type of practice, and perceptual ability. For example, when analyzing an incoming tennis ball, Lleyton Hewitt must process information on its flight, spin, and his opponent's position to determine the correct shot.