Researchers infer that the longer the infant takes to habituate to a new stimulus, the more it violates his or her expectations of physical phenomena. When an adult observes an optical illusion that seems physically impossible, he or she will attend to it until it makes sense. Until recently, psychologists believed that our understanding of physical laws emerges strictly from experience. But research shows that infants, who do not yet have such expansive knowledge of the world, have the same extended reaction to events that defy what is physically possible. Such studies conclude that all people are born with an innate ability to understand the physical world.