The term "representation" is a very slippery one in philosophy. The U.S. philosopher H. P. Grice ( some info can be found at http://www.artsci.wustl.edu/~philos/MindDict/grice.html ) distinguished two sense of the word "meaning," but his distinction has relevance to contemporary talk about "representation".

Grice asks us to reflect on the difference between sentences like these two.

1 -- Those spots mean measles

2 -- The "occupied" sign means that someone is using the lavatory.

He points out that if sentence 1 is true, then the occurrence of spots entails the existence of measles. Equivalently, if the occurrence of spots doesn't entail the existence of measles, then it's not correct to say that the spots mean measles. If, for example, the same sorts of spots can be produced by an allergic reaction to penicillin, then one should have said, "those spots mean either measles or an allergic reaction to penicillin."

On the other hand, the truth of sentence 2 doesn't entail that if the "occupied" sign is present, then someone is in the lavatory. "Occupied" means occupied, even if some practical joker has managed to trigger the sign on an empty toilet.

Grice calls the first kind of meaning "natural meaning," indicating that it's the sort of relation that exists when there is a natural connection between the sign and the thing signified, when it's a matter of natural law that the appearance of the sign is, as a matter of natural law, dependent on what the sign stands for. Because we have such relations in nature -- because smoke means fire, and bear scat means bear -- we can and do speak of "natural signs".

In the second case, however, the relation between the sign and the thing it stands for is not determined by any natural law. In fact, it was quite up to us human beings which sign -- which representation, which set of symbols -- to use to represent occupied-ness. We could have all used the sign the French chose -- "occupe" (with an accent). That is, the relation between "occupied" and being occupied is conventional -- a matter of social agreement, rather than natural law.

Now a really interesting question (to me, anyway) at the intersection of philosophy of language and philosophy of mind is this: is convention the only way to get non-natural meaning/representation? Because if it is, then we have a problem ab9out thoughts. The problem is this. Thoughts seem to be kinds of representations. When I think about Paris, I am representing the city of Paris in my mind. And when I think that Paris is lovely in the spring, I'm representing the situation of Paris's being lovely in the spring. But these representations have to be non-natural in Grice's sense. Why? Because it's perfectly possible for me to think about Paris even if Paris (alas!) isn't there, before me, in all its splendor. My Paris thought does not indicate the presence of Paris, in the way the spots indicate the presence of Paris.

But on the other hand, it can't be that the relation between my thought about Paris and the city itself is conventional -- it can't be like the relation between the English word, "Paris" and the city. Why not? Because to set up a convention, one needs to have thoughts that already have representational content. Suppose I want to use a certain neurological state as my personal symbol for Paris. To make that policy for myself, I'd have to form the intention to use that state to refer to Paris. But in order to form such an intention, I'd have to already have a way of representing Paris to myself -- and we're back where we started: with a representational state that can't have natural meaning, but that can't be conventional, either. The project of explaining how there could be this sort of in-between case -- a case of non-natural, but non-conventional meaning, or represntation, is one that has absorbed the energies of a number of prominent philosophers of mind, including Jerry Fodor, Fred Dretske, and Ruth Millikan. These philosophers all have theories purporting to show how a relation of non-natural, but non-conventional meaning could arise out of a natural world filled with merely natural signs.

Many philosophers want to reserve the term "representation" for items that have non-natural meaning. Some want to reserve the term "intentionality" (which in its broadest sense just means "aboutness") for the same purpose. Now the way in which the specialized neurons you speak of "represent" some specific orientation of a bar sounds to me like "natural" representation -- the firing of the specialized neuron is a natural sign of the presence of a bar oriented in that particular way. If that's right, then the philosophers alluded to above will balk at calling the neuronal firing a "representation" at all. But you don't have to argue with these philosophers about how to use words. Just ask them this: can non-natural mental representations (like my current thought about a bar oriented plumb to the plane of the earth) be somehow explained in terms of the neurological natural signs with which you are familiar?

I believe there has been a fair bit of discussion of mental health in the so-called "continental" tradition. One classic in that tradition is Foucault's Madness and Civilization. You might also want to look into the work of R.D. Laing, for example, The Politics of Experience, and the early work of Thomas Szasz, such as The Myth of Mental Illness. These are pretty radical viewpoints, and I'm not saying I agree with them, but both Laing's work and Szasz's early work are worth reading.

There is a piece on mental illness in the Stanford Encyclopedia.

Let's assume that had she not been given the amnesic medicine, we would agree that she experienced terror when the scalpel approached her eye. The question then becomes: why should the administration of the amnesic medicine change our view? Given your description of the medicine, it does not cause her not to have an experience; it just causes her to forget her experience. So, to answer your question, yes, she was terrified. She had an experience of terror, and she is now unable to recall that prior experience of terror.

You seem to be assuming that we must be able to remember an experience in order for it to have been truly experienced. I am inclined to deny this assumption. To help see why we should deny the assumption, consider a slightly different case. Suppose someone has an instant of terror and then dies. Would you want to deny that she experienced the terror, even though (due to her death) she never was able to form a memory of the terror?

I concur with Amy. We suppose that the eye operation itself took place, even th0ugh the patient forgot about it afterwards. It is natural to suppose that normally, in these cases, the experience of terror takes place at a specific time during the operation. So it is natural to suppose that the experience took place and was forgotten, just as the operation itself took place and was forgotten.

One unlikely alternative would be to allow for some sort of weird backward causation, whereby events that occur at one time can be undone by later events. Another, slightly less whacky, alternative would be to suppose that the properties of a person's experience at a given time are not fully determined by events that take place at that time, but rather are partly determined by their place in the overall pattern of the person's life.

How do any of us know that we haven't been similarly terrified? In typical cases in which an amnesic drug is administered, the subject will remember enough about previous and subsequent events to know that that had happened. However there might be exceptions. So I guess you'd only know for sure if you had a very detailed knowledge of your history.

I am due to have part of my right knee cap surgically removed, under general anaesthetic. There is a phenomenon called 'anaesthetic awareness', wherein the patient is paralysed but remains perfectly conscious. Apparently this is known to happen in about 1 in a 1000 cases. However I have heard it rumoured that amnesic drugs are standardly administered along with anaesthetics. So perhaps the incidence is higher. Should I be afraid?

'Water' is a natural-kind term, and the natural-kind that 'water' refers to turned out to be H2O. In every possible situation, 'water' refers only to quantities of H2O. Twin-water is of a different natural kind, say, XYZ. The idea is that physical natural-kinds are defined by what they are made up of. So, the stuff made up of XYZ (and not H2O) is not water.

The intuition that the XYZ-stuff on twin earth really is water may come from considerations like these: The XYZ-stuff on twin-earth looks and tastes just like water; it is used in the same way that we use water (brush teeth with it, wash clothes in it, etc.). But what determines the meaning of a physical natural-kind term (it is thought) is its physical make-up, not how it looks or what it's used for.

How it looks and what it's used for "fix the reference" of 'water:' The stuff that looks like *that* (pointing on earth to H2O) and is used for teeth-brushing, etc. is water. It turned out (centuries later) that that stuff is H2O--and it had been H2O all along. Twin-earthians fix the reference of their XYZ-term the same way: The stuff that looks like *that* (pointing on twin-earth to XYZ) and is used for teeth-brushing turned out to be XYZ. Because earthians and twin-earthians use the same descriptions to fix the reference of the relevant terms, it may seem that the Earthian and Twin-Earthian terms for the stuff that looks like water should be the same. But because the descriptions denote different kinds of stuff (H2O and XYZ), the words for the stuffs do not mean the same thing. Twin-Earthians may use a word that sounds like 'water', but it isn't 'water,' since it refers to XYZ.

Philosophers say, 'Water' "rigidly designates" water. That means that in every possible world 'water' refers to what is in fact water in the actual world--i.e., H2O. A world without H2O is a world without water.

It's perhaps worth saying here that there are philosophers whose intuitions are closer to those of the questioner. Gabriel Segal, a member of this panel, has written a nice book called A Slim Book About Narrow Content defending a view not that distant from the one mentioned.

That said, it's important to be clear about what the intuition is supposed to be. As Lynne said (hi, Lynne), the intuition is one about what the term "water" refers to. Or again, the intuition is supposed to be that, if Oscar says, "There's water on twin earth", he speaks falsely. One doesn't have to have that intuition. Some people don't. But before you decide whether you really do, it's worth thinking hard about the fact, mentioned by Lynne, that water is supposed to be a kind of stuff just like gold. Fool's gold isn't gold, no matter how much it looks like gold, and it wouldn't be gold even if it looked a whole lot more like gold, because fool's gold isn't the same kind of stuff that gold is. What we mean by a "kind of stuff" is a hard question, and it's particularly hard as concerns Oscar pre-1850. There are some nice papers by Mark Wilson, e.g. "Predicate Meets Property", on this issue.

The intuitions about the 'water' example that philosophers focus on are, as explained above, about reference. They are also about truth. It takes a little work to connect reference and truth to meaning. One line of thought goes as follows. Suppose that Oscar lands on Twin Earth. Both Oscar and Twin Oscar point to a sample of XYZ and say 'That is water'. What Twin Oscar says is true - he is speaking Twin English and Twin English speakers standardly call XYZ 'water'. But what Oscar says is false. He thinks that the stuff in front of him is water, the same kind of stuff he was familiar with on Earth. And that is the thought he is expressing when he says 'that's water'. But if what Twin Oscar says is true and what Oscar says is false, then their words must mean something different.

I concur with Deniz that non-philosophers often don't respond to the example in the way that many philosophers do - although as yet no seroious data on this have been gathered. Often they either don't share the intuitions about reference and truth or they do, but they remain convinced that what the Twins mean by their words is the same.

As Richard says (thanks for the mention, Richard), I am with the non-philosophers. I think that in 1750 the English word 'water' would have been true of XYZ as well as H2O.

For some discussion of how lay intuitions differ from those of philosophers' in respect of these matters, see my 'Reference, Causal Powers, Externalist Intutions and Unicorns' on my web page.

Most of these questions seem like empirical ones, and I'm not a neuro-scientist, so I'll skip them.

But let me ask a question back. Suppose Dr Jekyll performs an operation and, as a result, I seem to remember once sitting on a throne while some guy goes on about how, if I don't let his people go, there'll be plagues and pestilence and stuff. I don't see what that couldn't happen, as a matter of pure possibility. Would you want to say I remembered any of that? If all of us were born with that apparent memory, would it matter what we said to the previous question?