Jesse, how do you access the everything list?  I ask because I have not 
recieved my own posts in my inbox, nor have others such as Bruno replied.  I 
use yahoo email.  I may need to use a different method to prevent my posts from 
getting lost.  They do seem to show up on Google groups though.  There was 
never a problem until recently, so I'll see if this one works.

--- On Mon, 2/22/10, Jesse Mazer <laserma...@hotmail.com> wrote:
> Hi Jack, to me the idea that counterfactuals would be essential to defining 
> what counts as an "implementation" has always seemed counterintuitive for 
> reasons separate from the Olympia or movie-graph argument. The 
> thought-experiment I'd like to consider is one where some device is implanted 
> in my brain that passively monitors the activity of a large group of neurons, 
> and only if it finds them firing in some precise prespecified sequence does 
> it activate and stimulate my brain in some way, causing a change in brain 
> activity; otherwise it remains causally inert
> According to the counterfactual definition of implementations, would the mere 
> presence of this device change my qualia from what they'd be if it wasn't 
> present, even if the neurons required to activate it never actually fire in 
> the correct sequence and the device remains completely inert? That would seem 
> to divorce qualia from behavior in a pretty significant way...

The link between qualia and computations is, of course, hard to know anything 
about.  But it seems to me quite likely that qualia would be insensitive to the 
sort of changes in computations that you are talking about.  Such modified 
computations could give rise to the same (or nearly the same) set of qualia for 
the 'inert device' runs as unmodified ones would have.  I am not saying that 
this must always be the case, since if you take it too far you could run into 
Maudlin-type problems, but in many cases it would make sense.

> If you have time, perhaps you could take a look at my post
> http://www.mail-archive.com/everything-list@googlegroups.com/msg16244.html
> where I discussed a vague idea for how one might define isomorphic "causal 
> structures" that could be used to address the implementation problem, in a 
> way that wouldn't depend on counterfactuals at all

You do need counterfactuals to define implementations.

Consider the computation c(t+1) = a(t) AND b(t), where a,b,c, are bits.  
Suppose that a(t),b(t),and c(t) are all true.  Without counterfactuals, how 
would you distinguish the above from another computation such as c(t+1) = a(t)?

Even worse, suppose that c(t+1) is true no matter what.  a(t) and b(t) happen 
to be true.  Is the above computation implemented?

This gets even worse when you allow time-dependent mappings, which make a lot 
of intuitive sense in many practical cases.  Now c=1 can mean "c is true" at 
time t+1, but so can c=0 under a different mapping.

All of these problems go away when you require correct counterfactual behavior.

You might wonder about time dependent mappings.  If a(t)=1, b(t)=1, and c(t+1) 
= 0, can that implement the computation, considering a,b as true and c=0 as "c 
is true"?  Only if c(t+1) _would have been 1_ (thus, "c is false") if a(t) or 
b(t) had been zero.

Clearly, due to the various and time-dependent mappings, there are a lot of 
computations that end up equivalent.  But the point is that real distinctions 
remain.  No matter what mappings you choose, as long as counterfactual 
behaviors are required, there is NO mapping that would make "a AND b" 
equivalent to "a XOR b".  If you drop the counterfactual requirement, that is 
no longer the case.

--- On Mon, 2/22/10, Brent Meeker <meeke...@dslextreme.com> wrote:
> It seems that these thought experiments inevitably lead to considering a 
> digital simulation of the brain in a virtual environment.  This is usually 
> brushed over as an inessential aspect, but I'm coming to the opinion that it 
> is essential.

It's not essential, just convenient for thought experiments.

> Once you have encapsulated the whole thought experiment in a closed virtual 
> environment in a digital computer you have the paradox of the rock that 
> computes everything.

No. Input/output is not the solution for that; restrictions on mappings is.  
See my MCI paper:  http://arxiv.org/abs/0709.0544




      

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