From a point of view within the cognitive domain of science, we appear as organisms which are a product of natural selection. The outcome of the grand game of survival holds over us the power of life and death. The mind's experience of the playing field of that game as meaningful and real is unconscious recognition of this fact. The realness and significance of experience, in other words, arise ultimately from the fact of embodiment. That we apprehend the environment as a self-existent world derives from the fact that events around us (and sometimes far away) do indeed matter. As far as the Mind-Body Problem is concerned, the central point of embodiment is not that we are protoplasm, but that we are players in the game. It is the world in which we play that is the primary domain of our experience, the beginning point and end product of complex cognitive processes. Our brains are streamlined to exclude these processes themselves from cognition, just as the workings and controls of a well-designed aircraft are transparent, allowing the pilot's attention to dwell in air space. This is only possible because the aircraft itself embodies a great reserve of knowledge about aerodynamics, mechanical engineering, and so forth, which may be taken for granted.
The organisms that exist are those that have survived by taking reality seriously. We are committed to this game. Were it not so-- if we led a ghostly disembodied life unaffecting and unaffected by the world-- would we be compelled to regard experience as anything more than a dream? If indeed, in such a condition, we could experience anything at all! For consciousness itself is surely a motivated strategy in the game. Were we indifferent to the state of our tissues (or lacking them altogether), pains would not hurt nor would pleasures feel good. If we did not identify with the physicality, welfare, and purposes of the body, there would be little reason to take reality seriously enough to bother to represent it in perception. There would be no basis for experience.
The bridge between the domain of the organism, as a self-contained closed system, and that of the environment, is the organism's intentional mapping between these domains. Experience always informs the creature of its relationship to the world. This is obvious in the case of spatial relations: objects are perceived as distant or near in relation to the body. The fact that something tastes "good" is cellular knowledge, so to speak, of its chemical relation to that substance. Sometimes, of course, this knowledge is inaccurate or incomplete (there are poisons that do not taste bad, or bad enough to steer us clear of them!) The fact that an object looks near or far, or tastes good or bad, is an aspect of the creature's knowledge of what to expect from it and how to conduct itself in regard to it. All perception, in other words, is imbued with the priorities of the organism.
The most alien creature from outer space would probably share our elementary response patterns merely by virtue of being, as we are, a product of natural selection. Such is not (yet) the case for machines, but the issue of intentionality, and the role of embodiment that underlies it, is crucial to understanding what constitutes life and mind. In particular, it poses the question of whether, and under what circumstances, artificial life and artificial minds are possible.
The information processing model of mind assumes an input and an output, a formal system linking them, and a programmer-observer who intentionally defines the system in his own cognitive domain. The organic model of mind assumes a physical body, as part of a larger causal system, developing through natural selection in the course of long genetic histories. A cognitive domain belonging to the creature itself is thereby established. The information processing model has (erroneously) assumed that an organism or its brain can be exhaustively codified. A formal system can be completely specified because it is an intentional creation of the human mind. It contains exactly what was put into it by its creators. But a biological system is not the invention of its investigators, but part of the world-in-itself. Biological systems conform to our descriptions only in the way that the real business world conforms to the game of Monopoly.
The domain of information supplied to the computer, its operational guidelines, and its output alike have meaning only in the cognitive domain of the user. The desktop computer has no cognitive domain of its own because someone else has determined the relation between input and output, between its states and the world to which those states refer. Nor has it any motivation or basis on which to specify such a relationship itself. The basis for an organism's intentionality is its bodily insertion in the world, which provides the values, axioms or guidelines on which it makes its decisions and constructs its representations of the world. Consider the computer "Hal" in the film 2001. Hal was, in effect, embodied. The entire spaceship was Hal's body, and the humans on board were mere parasites initially tolerated because of their symbiotic relationship with the host. When the humans began to pose a threat, Hal acted in his own interest, and in what "he" believed to be the greater interest of the mission. The present day computer, we may be glad, has no body and no stake in the world. The current generation of digital computer is a tool of human purposes, not an imitation organism.
It is sometimes said that the computer has only "derived" intentionality and not the "original" intentionality of organisms. This distinction parallels that between third and first person points of view, respectively. But original intentionality is the only kind there actually is. The confusing notion of derived intentionality arises in linguistic analysis (where an intentional statement is a type of sentence rather than a type of action denoting the state of an agent). But if intentionality is rather a defining property of an agent, then no linguistic expression has intentionality-- derived or original-- since no linguistic expression is an agent. A book (or a statement) could only be intentional if it were itself an agent-- if, for example, it could write itself and read itself.
Descartes was probably the first to see the possibility of a mechanistic explanation of consciousness. By means of the coordinate system that bears his name, he discovered that geometrical figures could be expressed as equations, and vice-versa. The equivalence of geometry with algebra, of visible shapes with abstract formal operations, had escaped the Greeks in spite of their fascination with number and form. But this insight was the clue that illumined Descartes' search for the nature of mind as mechanism. Just as geometrical figures are generated by algebraic operations, so are the shapes and colors we experience in vision, for instance, generated by logical operations represented by physical events in the brain. The intuition of Descartes the mathematician was to see the relationship between brain and mind as like that between algebra and geometry-- a relationship above all intentional. 
The language of experience is as conventional as the language of numbers or words. In the meaning of each symbol we find nothing necessary in itself, but only whatever the mind has agreed to. The redness of the color red, the hurtfulness of pain, the spaciousness of space, the solidity of objects, the realness and externality of the world--all are conventions the mind has accepted as given. Cognition is like an interpreted formal system, one pressed into representational service. Other interpretations could be possible for a given system, and other systems could map the same territory. The subjectively experienced suchness and realness of experience derives from accepting the premises of one's cognitive system, in much the way that logical conclusions derive from accepted axioms, expressing the mind's irreducible intentionality-- its "animal faith" in its own cognitive axioms. This faith is underwritten by, and ultimately refers to, the fact that organisms in possession of such a system survive. We are here because we are just what we are, and the world is just as it is in our experience for the same reason.
Descartes sets out first to reduce physics to the mathematics of space. For him, extension in space is the only objective quality of matter, and space is in turn reducible to number through the coordinate system. Physical "movements" in the brain could thus embody logical or numerical operations, which in turn could represent spatial relations-- and hence exterior reality. The mechanisms which served as Descartes' model were unsophisticated-- clocks, windmills, programmed waterworks, etc. But even lacking the modern concept of information, Descartes understood that these were devices capable of representing, transforming and transmitting numerical operations-- in short, computers. He grasped that the brain is the organ of perception, and that the afferent nerves relay a display of signals, not a copy of the world.
Descartes had studied the optics of vision by dissecting an eye in such a way as to actually observe, from behind, the image projected upon the retina. Long before the invention of photography, the camera metaphor was suggestive-- and also misleading. For in no way does the mere transmission of an optical image in the eye explain the process of vision. If it did, we might as well imagine that television sets can see. Vision is rather an intentional process of interpreting the image. To the brain, an image is a pattern of signs to be given meaning rather than a copy of the world. This points to another way in which the camera metaphor is misleading. In looking at an object and at a picture or image of that object, we can see that they are isomorphic, and that there is an analogy between the lens of the camera and that of the eye. But this tells us nothing of intentional mappings, represented by neural transformations in the brain, as opposed to optical transformations taking place in the eye. We cannot conclude, on the grounds of the camera metaphor, that there is an isomorphism between our experience of the object and the object itself. To do so is to confuse the optical image with the experience that is somehow generated in the brain on the basis of that image.