in physicalism everything that is visually perceivable has a physical location.
I'm going to nit-pick you on use of language, here. Because wishy-washy, imprecise terminology ruins this debate.
Materialism (I prefer the term) just says that existence is defined by having mass*, a location, velocity, etc... When I say that Mars exists, there is a shared understanding between us of what I mean. I mean that the planet Mars is made of matter, it has a location in the universe, a velocity.
So it's abundantly clear that the statement "Everything that is visually perceivable has a physical location" is not true. "The perception itself" is merely a thought, an electrochemical process. So sure that has a location. But what the thought is "about" obviously does not.
In short: When you think of a pink unicorn, the thought has a location. The unicorn does not. Because the unicorn doesn't exist.
- What I said is that it doesn't apply because a human mind visually perceives a mental image, a computer doesn't. A computer has the data, and then projects it physically onto a screen. There is no point in the process where a computer visually perceives the image, before it is physically projected on a screen. In fact a computer can't visually perceive anything, because it doesn't have a brain with sense perception. So the example has no relevance.
Who's to say that a computer doesn't "perceive" things? Try defining "perceive" in a way that doesn't make you beg the question. You're asserting that a human brain can do something which a computer cannot. But what gives the brain that special capacity? I've been asking this question over and over with no answer.
It sure sounds like you're saying: "The human brain has a non-physical mind controlling it" therefore it can do things a computer cannot. That sure would be begging the question.
A computer does a lot of processing on data before it can be represented on screen. You can study GPUs and graphics algorithms for years and not have a firm handle on how it all works. (Again, I remind you that I'm a computer engineer)
The brain, while complex, is nothing more than a Turing Machine. (
https://secure.wikimedia.org/wikipedia/en/wiki/Turing_machine) It accepts input, processes the data, then produces output. It is bound by the same computational limits that any machine is.
Again: How exactly does Free Will work? Some gland, or chemical that violates physical law? And is it just humans? What about monkeys, dogs, cats, mice, flies, mites, bacteria, viruses, rocks? What causes the line to be drawn where it is?
What would happen if you made an exact, atom-for-atom duplicate of a person? Should we expect them to drop down dead because the copy has no "mind"?
Free Will is a binary proposition. You can either have it or not. There's no in-between. So, then at what point in the human development cycle does Free Will occur? Clearly, the mass of a few dozen cells shortly after conception doesn't have Free Will. But a grown adult does? So at what exact developmental period does Free Will occur? And what causes it to?
And even if you grant the existence+ of non-physical minds, any interactions between these worlds violate causality. If causality is not violated, then that means there's a set of physical laws governing the interactions. And then this "mind world" is just another corner of out everyday universe, and not "non-physical" at all.
From the very beginning of this debate, I've been trying to press for a definition of the term Free Will. Because you soon realize that violating causality isn't just a necessary consequence of Free Will, it is exactly what defines Free Will.
Free Will is nothing more than the belief that humans can violate physical law, because we think we're special.
*= There can theoretically be massless particles. But you get the point.
+= Again, though, it's not clear what "existence" even means when not talking about physical objects.