Correction and retraction re: Nature isn't so sloppy

From: Phil Goetz (
Date: Fri Sep 09 2005 - 12:54:36 MDT

--- Phil Goetz <> wrote:

> Making this mapping onto output states consistent, clear, and
> error-free requires a lot of engineering overkill. A neuron
> operates at a few millivolts, and its output, as a result, is
> "wrong" about 10% of the time. A silicon chip operates with
> about a 10-volt difference between its two states, in order to
> be almost error-free. We humans have gone from a reliability
> of .9 to 1-10^-14 or whatever - about a 10% improvement - in
> exchange for an increase in power requirements of 4 orders of
> magnitude.

I spoke of power but gave numbers in volts. Sorry.
A head dissipates about 25 watts, and has about 10^10 neurons.
A CPU uses, what, 35 watts or so, and can do roughly one
instruction at a time, but each one is much faster, about
one billionth of a second, whereas a neuron operation is around
1/200th of a second.

Calculated this way, and discounting a factor of 100 for
neuron redundancy, the neuron comes in just about 1 order
of magnitude ahead of the CPU. Remarkable. A further
discounting of the fact that we're comparing single pulses
to 1/10th of a floating-point operations would probably
make them come in even. (A Pentium IV takes about 10 cycles
per floating-point operation, averaged over time so that this
is factoring in pipelining and such.)

- Phil

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