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From: markrose@spss.com (Mark Rosenfelder)
Subject: Re: When is a simulation of a Y a Y? (Was Bag the Turing
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References: <D2D0sM.55o@spss.com> <D2IDnI.1C1@cogsci.ed.ac.uk> <D2KLCv.C23@spss.com> <D2pzFL.L38@cogsci.ed.ac.uk>
Date: Tue, 24 Jan 1995 22:31:53 GMT
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In article <D2pzFL.L38@cogsci.ed.ac.uk>,
Jeff Dalton <jeff@aiai.ed.ac.uk> wrote:
>>>In article <D2D0sM.55o@spss.com> markrose@spss.com (Mark Rosenfelder) writes:
>>>>The fact that we are not aware of everything outside the fovea being a blur
>>>>does *not* show that we have a "detailed internal representation".  Dennett
>>>>shows (in _Consciousness Explained_) that the notion that the brain fills
>>>>in some detailed picture of what the eyes see, even neatly airbrushing over
>>>>the blind spot, is a fantasy, a relic of the Cartesian Theater.
>>>
>>>Does Dennett show (a) that anyone interesting actually holds the view
>>>that the brain fills in or (b) that this view _is_ a relic of the
>>>Cartesian Theatre?
>
>I've returned to this point in the thread because I've just gone back
>and read the sections of _Consciousness Explained_ that deal with
>blind spots and "filled in".  So this is about Dennett and blind
>spots.  I don't say anything about "everything outside the fovea being
>a blur", though I suppose similar considerations might apply.
>
>[...] I do not agree that (a) Dennett shows that anyone holds the
>view of "filling in" that he criticizes or (b) that Dennett has shown
>this is a relic of the Cartesian Theater.  Nor has he shown that they
>use scare quotes because they're embarrassed.  His claim that Hardin
>can't "bring himself to say" plaid is filled in is unsupported.

You're reading Dennett here over-literally, just as you accuse him of
doing below.  Of course he hasn't *proven* that Hardin "can't bring himself
to say" plaid.  How could one prove such a thing anyway?  Dennett is pointing
out that Hardin describes filling in the blind spot with blue, but not with 
plaid.  He finds this suggestive, and I do too: it seems a stronger claim
that the brain has some kind of filling-in process for plaid.  So we have
some skepticism about a plaid filling-in process; Dennett then invites us
to apply this same skepticism to any kind of filling in of the blind spot.

>Let me present a quote from a recent net article (by Andrzej Pindor): 
>
>  In another posting I have pointed out that we sometimes act not only
>  on what is in our peripheral vision, but even on objects in the
>  surrounding area which we do not see, but know from previous
>  inspection that they are there.  Hence we _do_ have a filled-in
>  picture of what is around us.
>
>To me, at least, this "filled-in" is a perfectly reasonable way
>to talk and doesn't owe anything to Cartesian Theatres.  So I offer
>it as an example.  It's possible to say "filled-in" without getting
>into trouble.

Certainly we know things about the world even with our eyes closed;
but we still find it useful to keep them open, even in our own bedrooms
with nothing changing.  So Andrzej's remarks do not show that the brain 
fills in details that the eyes do not see (because of the blind spot or the
lower resolution outside the fovea); on the contrary, with our eyes closed
we have an even lower information content than non-foveal vision offers.

>But what about those other guys, Hardin at al?  When someone talks
>about "filling-in" part of the visual field, it can sound rather
>like they have in mind an observer looking at something projected
>on a screen.  But it seems to me that all they're really saying is
>that we don't notice the blind spots  [...]

Then why don't they say that?  

Dennett's citations are not from Usenet; they're from textbooks or books of 
philosophy, whose authors should be careful about what they're saying.
Hardin's (excellent) book, for instance, is an introduction aimed at
philosophers to what is currently known about vision.  He should (and
normally does) carefully distinguish what is known about vision (e.g.
that the blind spot is not directly perceived) from theories about why
it is not ("filling in").  If he doesn't do that, how can his readers
build reasonable, well-informed theories of their own?

One of Dennett's major points is that we overstate what we know about our
own perception; we get the facts wrong, or don't distinguish the facts
from theorizing about the facts.  That we don't see the blind spot is a
fact.  That it gets filled in is a theory, and needs to be argued for,
not assumed, and certainly not enshrined as the usual, neutral way of
talking about the phenomenon.  

>Now, when someone talks about "filling-in", we can think about what
>they say in more than one way.  We might try to figure out what
>they're talking about, and, sure enough, we find that there is a 
>blind spot and that we're not normally aware of it.  We might then
>wonder whether "filling-in" is really the best way to describe this
>or just what this talk of filling-in really amounts to.  

Exactly.  That's just what Dennett is doing, IMHO: wondering whether
"filling in" is the best way to describe what's going on.  If he hadn't
read these authors "the wrong way", if he had just cut them some slack
and let them write sloppily, he wouldn't have stumbled on such an
interesting question.  

>Indeed, I find it difficult to determine just what view Dennett thinks
>Hardin and the others hold.  When Dennett tries to say what it amounts
>to, he comes up with something so ridiculous (see e.g. what he says about
>"figment") that I find it hard to believe that anyone holds such a view.

Sure, figment is ridiculous; also very amusing.  But it has a serious point:
if this talk of filling-in doesn't mean that, what does it mean?  Why
talk that way if there's a better way of talking?  Or if one doesn't
accept Dennett's alternative, why not?

>Perhaps Dennett thinks they don't hold _any_ clear view.
>But if so, he doesn't do much to show that either.

Is his task to give proofs that other authors hold particular views,
or to explain how consciousness works?
