But the perceptual system is not co

But the perceptual system is not concerned with determining an object’s image on the retina. It starts with the image on the retina, and its job is to determine what object “out there” created the image. The task of determining the object responsible for a particular image on the retina is called the inverse projection problem, because it involves starting with the retinal image and extending rays out from the eye. When we do this, as shown by extending the lines in Figure 3.7 out from the eye, we see that the retinal image created by the rectangular page could have also been created by a number of other objects, including a tilted trapezoid, a much larger rectangle, and an infinite number of other objects, located at different distances. When we consider that a particular image on the retina can be created by many different objects in the environment, it is easy to see why we say that the image on the retina is ambiguous. Nonetheless, humans typically solve the inverse projection problem easily, even though it still poses serious challenges to computer-vision systems.