What the Neocortex Does

Gary Forbis GaryForbis at email.msn.com
Thu Aug 3 23:49:55 EST 2000

"Kevin K." <KK at _._> wrote in message news:3989AC71.7969B1CA at _._...
> Harry Erwin wrote:
> > You're missing my point. Symbols are signs. They belong to a countable
> > set. Wind-tunnel models can vary continuously (or discontinuously). That
> > matters--there are some applications (for example in hydraulic analysis)
> > where symbolic modeling encounters an intractable problem, but analog
> > modeling works fine.
> Intractability is a an issue relating to computational efficiency --
> i.e. the time or space required to perform the calculation. It has no
> bearing on Church's thesis. A Turing machine can be written to solve the
> hydraulic problem to any desired degree of accuracy because the TM has
> an infinite supply of time and space. It may take a while, but that's
> okay, because Church's thesis concerns computability in principle, not
> in practice.

I hate "in principle" arguments applied to real objects.  As you state
Church's thesis it does not apply to bats since they are real objects
performing in time and taking space.  You might as well be talking
about "in principle" angles dancing on the head of a pin.

> > Why do I care? Disambiguating an acoustic scene
> > based on multisensor data is very difficult because of all the ghosts
> > that have to be eliminated _sequentially_. Bats do it in real time. How?
> Real time has no bearing on Church's thesis. The issue is whether a bat
> can perform a calculation which a TM cannot, not whether a bat can
> calculate faster than a TM. (After all, TM's are the most inefficient
> machines ever conceived!)

In addition to applying an "in principle" argument to a real object you've
ignored your own in principle argument where you talk about "to any
degree of accuracy" which is not the same as "the same."  Church's
thesis doesn't address the very issue you say is the issue, which is,
"whether a bat can perform a calculation which a TM cannot."  I'd
think the issue is whether or not the bat is performing calculations at
all when it does what it does.  Is a rock performing calculations when
it falls?

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