IUBio

Toward a Science of Consciousness 1998

Neil Rickert rickert at cs.niu.edu
Sat Apr 25 17:30:02 EST 1998


modlin at concentric.net writes:

>In <6htajh$rq2 at ux.cs.niu.edu>, rickert at cs.niu.edu (Neil Rickert) writes:
> [snip]

>>You seem to have entirely missed a point I made.  Namely, there might
>>be a completely different way of describing the internal operations
>>of a computer, such that under this different internal description the
>>computer is executing a completely different algorithm.  If it is
>>the abstract computation that matters, then I am suggesting that the
>>abstract computation being performed is not determined by what happens
>>in the machine, in the sense that there are completely different
>>ways of assigning algorithmic descriptions to what happens physically.

>Let's focus on this point very closely.

>Consider a very simple computer.   It's called an "OR gate".   It has 
>two external inputs, and one external output.

Is this an abstract Turing OR gate (if there is such a thing).

Let's instead consider a real OR gate.  To keep it simple, lets suppose it
uses CMOS with a +5v voltage supply.  What it does, is it produces a voltage
output depending on two voltage inputs.

>The function it computes is "logical OR".   If either of the inputs is 
>active, the output is active.  If both inputs are inactive, the output 
>is inactive.

You are quite mistaken.  Of course it computes AND.  We assign TRUE
to voltages near 0, and FALSE to voltages near +5v.  Using this
assignment of TRUE and FALSE to generate a truth table, you can
easily see that it computes AND.  But, of course, we are
oversimplifying.  We are ignoring one of its inputs, the input
connected directly to the power supply.  If we take that input as
part of the data being processed, then it is computing a rather more
complex function.

>I say that the function it computes is determined by whatever is inside 
>the black box of the computer, and will remain the same no matter how 
>you choose to describe it.

And I say that what it computes depends on how we describe it.  I
have just demonstrated this by describing it such that it computes
AND.  Nevertheless the causal operations remain unaffected by the
choice of description.




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