> From: "Cozins, J.L." <jlc495@soton.ac.uk>
> Date: Wed, 22 May 1996 21:46:08 +0100 (BST)
>
> When we do something consciously we do it deliberately or knowingly,
> but to do something automatically or without having to think about it,
> is to do it unconsciously.
>
> Libet devised an experiment to demonstate the relationship between
> consciousness and cause. He asked a subject to stop a clock within
> sixty seconds. Lets say he did this after 25; thus t=25. He then asked
> the subject at what time he made the decision to stop the clock at 25
> secs past. He said after 23; thus d=23. Therefore it would be decision
> (d) before the time he stopped the clock (t) or to work out the
> reaction time, t-d. But the motor action-m (the actual physical
> stopping of the clock) also had to be considered.
The motor potential is not the stopping of the clock, it is the
event-related potential that precedes a movement; the brain "trigger" of
the movement.
> Logically the
> decision to stop the clock would be made before the motor action
> (d>m>t). However, this is where the experiment becomes problematic. The
> motor action had already begun before the decision had been made.
It's not the motor action that started before the decision, it is the
motor potential, an electrical event in the brain.
> But
> how could he have started to stop the clock before making the decision
> to do so? Could it be due to the evoke potentials of the decision and
> of the motor action -the signals sent from the brain and the build-up?
This sentence is not at all clear; I really cannot tell whether you
understand what you are saying -- and kid-sib certainly couldn't come to
an understanding about it based on what you just said.
> If this is the case, then the equation would alter and would now read
> DEP>MEP>D>M>P. Therefore if the DEP caused the Decision and the MEP
> caused the Motor action, then both of the evoke potential processes
> would be unconscious ones, as you don't consciously decide to do
> something. The action of stopping a clock should theoretically be the
> result of a conscious decision, but the DEP and MEP must come first,
> thus making it an unconscious one and also explaining the problem of
> consciousness as a cause.
Libet did not measure a DEP, just a MEP. He talked about vetoing a
decision after it was made, which we feel we can do, but that was not
actually tested (how could it be?).
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