Greg,
For your EEG problem, there are "30 measures" taken across a five minute
interval, but you don't say how many leads per subject. Are you using a
standard 19-lead EEG configuration? How many active leads per subject?
You say you can't equate the order in which the measures are taken for
one subject with the order in which they are taken for another. Have I
got that right? If so, then you can't compare across subjects, can you?
You say there is a temporal window of 2 seconds, within which analysis
occurs. I take that to mean you sample 2 sec. of EEG from each lead
(simultaneously? in succession?). So within a five minute period, for
each lead there are 30 samples, each one about 2 sec. long. Correct?
Since you don't say otherwise, I assume that during the five minutes of
EEG collection your subjects are just sitting there. I.e., during the
five minutes, there's no reason to think they switch from one type of
mental processing to another, is there? (or any such switching is random,
since the Ss are just asked to sit there, or whatever...). There are
task-dependent shifts in EEG frequency, both between L/R hemispheres and
posterior-frontal, which is why I ask.
If all this is reasonably accurate, then it seems to me that each *lead*
is the unit of measurement. You want to know that the error of
measurement per lead is relatively stable, before you proceed to do
cross-lead (but within one subject) comparisons. The cross-lead
comparisons are what will eventually yeild up the information as to
whether or not there is one (or a few) brain locus from which the alpha
frequency is generated, or at least pulsed, timed, or turned on/off.
Brains, like faces show individual differences. So whether or not a
"central locus" for individual one is in the exact same spot as the locus
for individual two is irrelevant. What I mean is, the *group* average
locus is less interesting than the fact that you can (eventually) pinpoint
a locus for an individual person with reasonable accuracy.
This isn't "the answer" yet, and I'm sure others on this list will have
more sophisticated suggestions than I, but I thought it would help to
clear away some of the underbrush & facilitate the discussion.
Mike
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* Michael Wogan, Ph.D., J.D. Department of Psychology *
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