The way we see things is more complicated (复杂的) than we imagine. Our eyes give us information all the time. But our brains decide what is 1 to us. For example, if you 2 a crowded street, you will see many faces. But you will probably not really notice them. But if you see someone you know, you will 3 him immediately. From this example we can see that your brain chooses the visual information which is 4 to you, and rejects the information which it does not need. The way your brain explains that information depends on the knowledge you have about the world. And all this happens in 5 a second.