Think for a moment about a baby's world. You give the baby a toy. How does he know whether this toy is a new one that he hasn't seen before or an old toy from his toy box?
He has to bring up his mental images of his toys and decide whether this toy in front of him matches the images of the toys he's already played with or not. Psychologists suggest that babies remember the features of their toys: color, shape, and specific features such as button eyes, floppy ears, or soft fuzzy texture.
What do babies' perceptions of toys have to do with you as an adult? You perform the same mental comparisons when you meet someone new. You may even think, "He looks familiar. Have I met this person before?" Or you may notice specific features such as his hair and think, "He reminds me of Uncle Jack, who has hair like that."