My aplogies to Dretske, after writing this I discovered that Dretske has heard of Russell's causal theory, but he remains blythly impervious to that argument, and remains a staunch defender of naive realism.

Dretske F. (1990) Seeing, Believing, and Knowing. In: D. N. Osherson, S. M. Kosslyn, & J. M. Hollerbach (Eds.) Visual Cognition and Action: An invitation to cognitive science. 129-148.

p. 136

"Our sense perception of objects is itself direct and unmediated. In other words, we may come to know (see) that [a perceived object] is a cat (a fact) by the way it appears, but what we see (the object) is the cat itself, not its appearance."

Dretske discusses the choice between Direct (Naive) Realism, and Representative Realism (also called the Causal Theory of Perception) as follows:

p. 137

"Indirect Realists maintain that we are directly aware of mental objects - images - in hallucinations and dreams. Aside from the cause of the experience, though, there is no reason to distinguish between these illusory experiences and our ordinary veridical perception of (physical) objects. In both cases we are directly aware of the internal mental representation. When we speak, as we commonly do, of seeing an ordinary object (like a cat), we are, if we speak truly, being caused to experience some catlike image by a real cat (a real cat that we do not directly perceive). When we hallucinate or dream of a cat, there is no such external cause - hence, we speak of these experiences as illusory. In all cases, though, it is the image that we directly experience. Only the cause of the experience is different.

So Dretske is fully aware of the representationalist position and Russell's causal theory of perception, and he characterizes it accurately. But now hear how he dismisses it.

p. 137 (continued from above)

"Direct Realists try to counter this, and related arguments, by insisting that although sensory perception of real objects requires the having (and thereby the existence) of internal representations, and though such representations in fact determine the way these objects look or appear to us, there is no reason to suppose we perceive these representations themselves. We perceive a cat by (internally) representing a cat, not by perceiving an internal representation of a cat." (my emphasis)

Wow! Incredible! Does Dretske really not see the contradiction in these statements?

There is a very good reason to suppose that we perceive the representations themselves, because in the illusory case there is no cat anywhere to be found, and therefore the three-dimensional volumetric colored image that we hallucinate is itself the representation of the cat. Now whether you choose to describe this process as "internally representing a cat" or "perceiving an internal representation of a cat", is just a matter of semantics. But in any case it is clear that your brain constructs SOMETHING in the illusory case, and that something is three-dimensional, volumetric, and colored and shaped like a cat. In fact the cat you believe you are seeing in your hallucination is itself the representation constructed by your brain.

The only way I can stretch my mind around Dretske's explanation is by assuming that the volumetric image of a cat "supervenes" on a non-spatial symbolic representation of a cat in your brain, which means that you can have volumetric spatial experiences with greater information content than that encoded in the corresponding neurophysiological representation.

But of course that just pushes the mystery on to the meaning of "supervenience", which might be defined as "information content that is experienced, but is not explicitly represented in any physical medium or mechanism." Until someone can demonstrate the principle of supervenience in a simple artificial sensory system, this "explanation" is as mysterious as the property of consciousness it is supposed to explain. For example, show me a computational device that can "report on" or provide output of data or information which is not actually encoded in that machine. Information theory shows that this is impossible in principle, because information cannot exist without a physical medium or carrier to code that information.

When Dretske says "there is no reason to suppose we perceive these representations themselves. We perceive a cat by (internally) representing a cat, not by perceiving an internal representation of a cat." he is professing the same kind of magical explanation as Descartes proposed when he claimed that the soul in the pineal gland does not even "see" the images transmitted to it from the sensory organs, but rather, as soon as the image arrives at the pineal gland, the soul immediately experiences not the image itself, but the external world directly.

In the words of Bertrand Russell, "So long as we adhere to the conventional notions of mind and matter, we are condemned to a view of perception which is miraculous. We suppose that a physical process starts from a visible object, travels to the eye, there changes into another physical process, causes yet another physical process in the optic nerve, finally produces some effect in the brain, simultaneously with which we see the object from which the process started, the seeing being something 'mental', totally different in character from the physical processes which precede and accompany it. This view is so queer that metaphysicians have invented all sorts of theories designed to substitute something less incredible. But nobody notices an elementary confusion". (Russell 1927, p. 137 - 143)

But what is most remarkable about these absurd contradictions is that nobody is going to call Dretske on this because they are all naive realists so they can't even see the contradiction!