[From Bill Powers (2007.01.05.0930 MST)]
Gary Cziko 2007.01.05 09:10 CST –
In the Libet experiments, the
subject agreeing to take part in the experiment is similar to driving the
car. The subject cannot just sit there and do nothing while watching the
clock as that would cause a higher-level error to the controlled
perception of being a cooperative subject. So the higher system regularly
changes the reference level of the subject’s hand position to move which
is recorded by Libet as the “readiness potential.” The fact
that there is no conscious awareness of this higher-level activity is
interesting, although it doesn’t make it impossible for the subject to
decide for whatever reason that he or she no longer wants to
participate in the experiment and do no more wrist flicking.
I agree, pretty much. But who says that the initiation of the readiness.
potential is unconscious? The way I see it is this. The person
deliberately, and consciously changes the reference level for the
state of the finger or wrist. That starts the voluntary action. Then the
person switches attention to the clock and waits for his/her finger or
hand to start moving, which takes a small fraction of a second, and
finally notes the clock reading at the moment when the first movement is
sensed. The clock reading is now considerably later than it was when the
act was initiated. Then the person has time to interrupt the act or
change it before it finishes. All actions have a beginning, a middle, and
an end, even when we perceive them as single “events.”
The question that will be raised is “How can the experimenter tell
when the initial conscious willing takes place?” Of course the
answer to that is that the experimenter can’t tell. Only the subject is
in a position to know that. But the experimenter can measure the initial
readiness potential, and then ask the subject if there was a moment
before the action when the subject willed the action and the action had
not yet actually occurred. We don’t usually notice that lag, but once
attention is called to it, it is definitely there – isn’t it?
A variation on the experiment might help. Suppose that sometimes, the
apparatus that detects the readiness potential triggers a flash of light
or a beep as soon as the potential occurs. Since this is a good third of
a second before the movement actually begins, the subject should be able
to say when the flash or beep occurred in relation to the initial act of
willing and the subsequent result of a perceived movement. I think a
third of a second is long enough for a discrimination to occur at that
level of perception.
Best,
Bill P.
···
If functional neuroimaging ever
develops to the point where there is very fine spatial and temporal
resolution, it may be possible to see HPC in action, with cascading
changes in references levels caused by error signals at higher levels. In
the meantime, I wonder if there aren’t experimental techniques like Libet
has used that can give us better insight into how HPC works and what it
means for issues like free will.–Gary
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