"“Continuously Updated Virtual Reality” is the idea that every brain constructs a virtual reality model of the world through which the animal is moving. The virtual reality software is continuously updated in the sense that, although it might theoretically be capable of simulating scenes of wildest fantasy (as in dreams), it is in practice constrained by data flowing from the sense organs. What the animal perceives is a virtual reality rendering of objects in the real world. Visual illusions such as Necker cubes and other alternating figures are best interpreted in these terms. The data sent to the brain by the retina are equally compatible with two virtual models of a cube. Having no basis to choose, the brain alternates. The virtual world that our brain constructs is, no doubt, very different from that of a squirrel, a mole, or a whale. Each species will construct virtual models that are useful for its particular way of life."