Have you ever asked yourself why you have two eyes instead of one, three, or even hundreds as some insects have? Have you wondered why your eyes are set close together on the front of your face rather than on the sides of your head, as on animals like rabbits, antelopes, and horses? The reasons are simple -- and important to the way you see the rest of your world.           Your eyes are like two small cameras. A camera catches an image of an object and records this image in miniature on a small piece of film. Similarly, when you look at something, each eye takes in what it sees and sends this image to the back of the eyeball. From each eye, an optic nerve then sends the image to the brain. Because your eyes are set close together, they view the world from about the same height but from slightly different angles. While your right eye sees an object a little to the right, your left eye sees the same object slightly to the left. Working as a team, the eyes send the images to the part of your brain called the cerebral cortex, which combines them into a single, centered image.          Seeing with two eyes working together is called stereoscopic vision. This allows you to view the world in three dimensions, or 3-D. These dimensions are height, width, and depth. Sensing depth allows you to judge the distance between you and the objects you see. It also helps you to adjust to the changing angle at which you see something as you move closer to or farther away from it. As you walk along a sidewalk, for example, seeing in stereo helps you to know how close you are to the street, how far you need to walk to arrive at a certain building, and how close you are to stepping on a rock or a piece of glass. As your body moves, your eyes give you a continual flow of information about where things are in relation to where you are.           If images are coming from only one eye, however, only two of these dimensions - height and width - can be sensed. A world seen with one eye is thus two-dimensional, as in a photograph. The sense of depth is lacking, making it more difficult to move around safely.           Now consider why your two eyes are located on the front of your face. Think of other animals with this same arrangement. Some examples are lions, wolves, and owls. What do these creatures have in common? They are all animals that hunt. These animals have eyes facing directly in front of them. This provides a field of vision that is about 180 degrees wide, like a half-circle. This kind of sight is called binocular vision.           On the other hand, animals that are hunted have eyes on the sides of the head. This provides nearly a 360-degree field of vision. Because these animals need to de ready to run at any moment in order to stay alive, they need to see things coming from the sides and from behind. However, without stereoscopic vision, these animals have a more difficult time determining how far away a threat is. This article would most likely be found in a   _  .
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