X-Message-Number: 13009
Date: Mon, 27 Dec 1999 14:27:55 -0500
From: Daniel Crevier <>
Subject: The downloading thought experiment
References: <>

Subject : the downloading thought experiment.

My revival of the downloading thought experiment two weeks ago has 
elicited many comments. Among them was a long discussion involving 
mostly Robert Ettinger and Mike Perry as to whether a mere simulation 
can be "as good as"  the real thing. Needless to say, I am on Mike's 
side and my answer is yes.

In fact I think the downloading thought experiment, if we look at it a 
little more closely, provides a convincing argument to this effect.

First, let us review our premisses carefully. They are :

- consciousness can be explained, understood and accounted for in terms 
of purely physical phenomena. "Self circuits", "standing waves" or any 
other phenomena deemed necessary to generate consciousness must be 
physical in nature, and therefore describable in quantitative terms. 
This implies that they can be simulated by a digital computer, to any 
desired degree of accuracy.  If they can't, then we are back to 
mysticism, and I won't follow anyone on these grounds.

- This being the case, then it is possible to carry out a simulation of 
all or part of the brain that would have the same input-output 
properties as the original organ.  Input and output do not have to be 
electrical: for example, the simulation could be connected to a 
biological neuron through an artificial half of a synapse, the other, 
original half  residing on the biological neuron. The artificial half 
would emit or absorb neurotransmitters in just the right way to 
interface correctly with the biological half. If other kinds of signals 
(such as electromagnetic) are eventually discovered to play a role in 
communication between different parts of  the brain, the simulation will 
also generate them just as  the biological tissue did.

Suppose now that we are partway throught the downloading of a human 
subject. The part of his brain that processes images from his left eye 
has been turned into a simulation performed by a digital computer 
(either sequential or parallel, it doesn't matter as long as it is fast 
and accurate enough). This simulation has the same input-output 
properties as the original tissue, and is connected to the rest of the 
brain and to the eye as described above. The rest of the brain, which 
includes the higher-level decision centers and the speech centers, is 
entirely unaffected. In particular, images coming from the right eye are 
still processed by the original tissue, and the subject can compare what 
he sees through his left eye to what he sees throught the other eye. We 
now show to the subject's left eye, invisible to the right eye, the 
image of a luscious red tomato in green foliage, and ask him what he 
sees. What will he answer? Let's try different possibilities.

First pass: no information, no qualia.  Some will say: "Since a 
computer simulation of a thuderstorm is not a thunderstorm and has never 
made anyone wet, the artificial brain part is of absolutely no use to 
the subject, who will answer that he is blind in his left eye and cannot 
tell us what he sees." But that's difficult to swallow because the rest 
of his brain is still getting exactly the same signals as before from 
the artificial part. These signals encode a description of the contents 
of the image, and the subject should at least be able to inform us of 
these contents. So:

Second pass: information but no qualia. "All right", says the 
opposition, "the subject will be able to describe the image to us, but 
I'll be damned if mere bit-flipping in a digital computer can generate 
qualia. Describing an seeing an image are two very different things. Our 
subject will therefore behave as so-called blind sighted patients, who 
have suffered damage to the visual centers of their brains. They 'feel' 
blind  but, due to some residual visual processing ability, perform 
better than chance when asked to describe what they should see. Our 
subject would therefore tell us that he still feels blind in his left 
eye, but that somehow, when we ask him what he sees, the answer 
assembles itself of its own in his mind".  My answer to this is that 
such an outcome is impossible because it contradicts our premisses.  But 
first, a short aside. Notice that the subject performs a lot better than 
blindsighted patients because, since he is getting *all* the visual 
signals of his former biological visual centers,  he can describe the 
tomato in as much detail as we want. He can tell us the shape and number 
of the leaves surrounding the tomato, and whether it is completely ripe 
or still has some green in it. If he has any talent, he can even draw
the tomato. If this is the case, are you seriously suggesting that he is 
not forming  a mental image of the tomato?  I claim that he is because 
the representation of the tomato in the computer simulation, and the 
signals describing it to the rest of the brain, *are* the mental image. 
Which leads us to my main argument. 

Remember (again) that the simulation has the same input-output 
properties as the original brain tissue it replaces. The remaining, 
unaffected, biological tissue, of course has the same input-output 
properties  as before. Further, the simulation and the remaining 
biological part of the brain are interconnected exactly as the original 
biological tissues were. Therefore the overall system, made of the 
simulation and the remaining biological brain, has the same global 
input-output properties as the original, biological brain. If the input 
is the tomato image and our question as to what the subject sees, the 
output, which is the subject's verbal answer, should be the same as 
before. Therefore, the subject should not only describe the tomato, but 
report that his perception of it is unaffected, and that he sees as well 
throught his left eye as through his right eye.  Which leads us to our

Third pass: information but "false" qualia. "Well," replies the 
opposition, "this just shows that we can't believe what the subject is 
saying. He has been already partly  transformed into a zombie by the 
experiment, and his sayings do not reflect the true contents of his 
consciousness." Again, this cannot be: the subject's decision and speech 
centers have been left unaffected, and I don't see how the simulation of 
the visual centers can control them. Therefore if the subject reports 
that he still perceives the qualia of red and green from his left eye, 
it is because he really and truly perceives them.  Which demonstrates  
that "mere" bit flipping in a digital computer can generate qualia. 

QED, I think.

Happy millenium to all, 

Daniel Crevier

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