Which part of receptor (eye) in combination with signal interpreter (in this case the cerebrum) did I fail to clarify? — Barry Etheridge

The important part: their cause, which you explicitly omit:

"You don't see light. You respond to an electrical signal transmitted from a receptor in your eye which obviously isn't light at all." — Barry Etheridge

(..and obviously no-one claimed that light would somehow occur inside the nervous system.)

One photon is sufficient to cause a detectable signal and response, but without photons you'd see nothing. Instead you assume a "signal interpreter" fabricating mental "movies" with lights etc., of a world in the dark, which is as absurd as solipsism.

I didn't. You apparently have. I'll let you sort it out.

We do of course know that the visual cortex can and does operate without photons because we have visual dreams and hallucinations. We can also see pure black even though it releases no photons in our direction at all. What you seem reluctant to admit is that what we see is a construct bearing little or no resemblance to what is actually sending photons toward us. Why you should be so reluctant to accept what every neuro-scientist accepts as a matter of course, I have no idea.

You wish. But to also revolve around other things wont make 'The earth revolves around the sun' false. — jkop

It most certainly does. The earth revolves around its axis. It orbits the sun!

If Hoffman has arrived at his theory that reality is nothing like what we perceive, then upon what does he base this theory? It cannot be based on studies of the brain because that is only possible via the very perception that he claims does not show things to be anything like what "they really are". If this were true, then the brain he is studying could not be anything like the "real brain", and his theory refutes itself by undermining its own premise.

So reality must be like what we perceive? Except then his empirical studies are reliable, and so his conclusions justified. Therefore the theory that reality must be like what we perceive refutes itself.

Not at all; it just means his theory is mistaken. I mean, it's not as if it follows logically that, if empirical studies are reliable, any theoretical conclusions about them must be correct. His theory must be wrong since it invalidly relies upon the very thing it purports to refute.

So let's say I see a yellow shape on my computer screen. I look at it closer, say with a magnifying glass, and see that it's actually a mixture of red and green. I then conclude that what's really going on is different to what I ordinarily see. Are you saying that this methodology is flawed, and so my conclusion mistaken?

No, they are just two different aspects, in two different contexts, of what you see. Why must one be 'correct' and the other 'incorrect'?

If you want to say that what is seen is perception-independent then it seems that at least one of them must be incorrect. It can't be both an all-yellow colour and a red-green mix.

I don't know what you mean by "perception independent"; do you?

It's what realists argue for. It's what exists even when we're not looking.

I consider myself a realist but I wouldn't claim that colours exist apart from perception; only that (some of) the conditions for perceiving are not themselves perceived, but thought in different ways. But I don't think this translates as 'reality is different to what we perceive', either. There is no reality apart from what we perceive and think about what we perceive. The very idea is incoherent.

I don't see what's realist about that. Sounds more like idealism or phenomenalism or some other anti-realism.

It cannot be based on studies of the brain because that is only possible via the very perception that he claims does not show things to be anything like what "they really are". — John

There is a rational argument at the base of this. The brain evolves to represent the world in terms of our interests. And so our own interests get baked into our states of perception. We are not in the business of seeing things as they really are, but only as they really matter.

Everything we perceive is filtered through subjectivity. So, no matter how objective we want to become, there will always remain a remnant of subjectivity.

We do of course know that the visual cortex can and does operate without photons because we have visual dreams and hallucinations. — Barry Etheridge

Without photons your visual cortex "operates" only hallucinations, in which nothing is seen. That's why they are called 'hallucinations'.

. .what we see is a construct bearing little or no resemblance to what is actually sending photons toward us. — Barry Etheridge

And how could you see that it has a different construction than what we actually see? Divine vision? Or is it somehow implied by the trivial fact that we sometimes mistake the things we see for something else?

I think it is obviously true that what causes an object to appear rectangular is its real construction. The brain does not fabricate a rectangular picture of an object explained away as invisible.

"The world presented to us by our perceptions is nothing like reality".

This what Hoffman claims. But if our perceptions of the brain are nothing like the real brain, then we cannot base any theories about what reality is like or not like on them.

That is the only point I was making. Personally I don't think the notion of 'things as they really are' is intelligible in anything more than an empty formal sense, as a logical distinction from the idea of 'how things are for us'.

John can you in a simple way your feelings on what a logical idea of what things are for us?? just curios of ur thoughts

Sounds more like idealism or phenomenalism or some other anti-realism. — Michael

Idealism (subjective at least) proposes that reality is exhaustively constituted by ideas. I haven't said that, nor does anything I have said entail that. So my position is certainly not subjective idealism; although it's not too far from objective or absolute idealism. But that position is indistinguishable from realism.

And my position is not phenomenalism because i allow for real causation and conditions for the possibility of experience that are not themselves directly experienced.

As to anti-realism; I don't think that is even a coherently definable position; other than being a negatively reactive rejection of what all realists are (incorrectly) purported to be necessarily claiming.

Idealism (subjective at least) proposes that reality is exhaustively constituted by ideas. I haven't said that, nor does anything I have said entail that. So my position is certainly not subjective idealism; although it's not too far from objective or absolute idealism. But that position is indistinguishable from realism.

And my position is not phenomenalism because i allow for real causation and conditions for the possibility of experience that are not themselves directly experienced.

As to anti-realism; I don't think that is even a coherently definable position; other than being a negatively reactive rejection of what all realists are (incorrectly) purported to be necessarily claiming. — John

Realism, as explained here, specifically in the context of naïve realism, is the theory that the objects we see exist and retain the properties we perceive them to have even when they're not being perceived.

As explained here, realism is the theory that "a, b, and c and so on exist, and the fact that they exist and have properties such as F-ness, G-ness, and H-ness is (apart from mundane empirical dependencies of the sort sometimes encountered in everyday life [e.g. tables are man-made]) independent of anyone's beliefs, linguistic practices, conceptual schemes, and so on."

You don't seem to be arguing for any of this, which is why I don't see what's realist about your position. And regarding anti-realism, it is by-and-large simply a rejection of the above. If you agree that the above doesn't make sense then you're agreeing with anti-realism.

So my position is certainly not subjective idealism; although it's not too far from objective or absolute idealism. But that position is indistinguishable from realism. — John

Well, objective idealism "is an idealistic metaphysics that postulates that there is in an important sense only one perceiver, and that this perceiver is one with that which is perceived"¹ and absolute idealism "can generally be characterized as including the following principles: (1) the common everyday world of things and embodied minds is not the world as it really is [my emphasis] but merely as it appears in terms of uncriticized categories; (2) the best reflection of the world is not found in physical and mathematical categories but in terms of a self-conscious mind; and (3) thought is the relation of each particular experience with the infinite whole of which it is an expression, rather than the imposition of ready-made forms upon given material."²

Which is your view closest to? The second certainly doesn't sound anything like realism (well, maybe indirect realism), and quite explicitly supports Hoffman's (and apokrisis') claim, contra your own.

¹ https://en.wikipedia.org/wiki/Objective_idealism
¹ https://www.britannica.com/topic/Absolute-Idealism

The brain does not fabricate a rectangular picture of an object explained away as invisible. — jkop

Except that is exactly what happens in one of the most famous optical illusions. We simply do not see an exact map of the photons received at the retina. Apart from the fact that the very structure of the eye makes that impossible (not least because there's a hole in the retina) we know that the information sent to the visual cortex is heavily manipulated, most obviously in the resolving of two different images into a single one (you seem to have conveniently forgotten that we have two eyes in conflict at the reception end).

The famous yellow cast problem faced by photographers gives more than adequate evidence that the colours we see are adjusted constantly by the brain according to the time of day. We know that people whose languages do not distinguish particular colours cannot see those colours as distinct without considerable effort. Again from photography we know that parallax issues are straightened out. From the famous shrinking room illusion which is just as effective in 3D as in 2D we know that the apparent size of objects is often completely a matter of cognitive process.

The evidence is overwhelming that what we see is a heavily edited version of the images falling on our retinas and that our vision is impressionistic at best. It bears as much relation to reality as it needs to allow us to move around and manipulate objects without falling over too often and no more. The brain is always the dominant partner in the sensor, signal, display loop to the extent that it can literally make us see things that are not there. That is the inescapable conclusion of a vast wealth of experimental evidence, believe it or not!

One photon is sufficient to cause a detectable signal and response, but without photons you'd see nothing. — jkop

Only if you are a frog. Humans require several photons to stimulate a rod/cone. Have seen estimates from 3 to 7. But anyway, one is not enough.

Except that is exactly what happens in one of the most famous optical illusions. We simply do not see an exact map of the photons received at the retina. — Barry Etheridge

We certainly don't! This is my favourite optical illusion:

Everything we perceive is filtered through subjectivity. So, no matter how objective we want to become, there will always remain a remnant of subjectivity — saw038

So here's another usage of "objective," and I think it's a fairly common one: people can be objective. What exactly does it mean for a person to be objective?

To avoid cognitive biases, e.g. confirmation bias.

But to avoid confirmation bias, we usually take people out of the investigation altogether, don't we? Double-blind studies and such?

Is it really possible for a person to overcome, transcend, negate... whatever you'd call it.. their own biases?

There is no reality apart from what we perceive and think about what we perceive. — John

Or in other words, you're not at all a realist in the conventional sense of that term.

Except that is exactly what happens in one of the most famous optical illusions. We simply do not see an exact map of the photons received at the retina. . . . — Barry Etheridge

Don't you get it yet? There is no need for an exact map when we see objects directly. From illusions it does not follow that all we see would be illusions.

Also, in order to know that something is an illusion in the first place, you'd need to be able to know what it's really like in contradistinction to what you thought it was like.