Hi, thanks for the explanation. That helped me out a lot.
What I described previously was essentially a block design task. We have
another paradigm which is jittered event related. Each event is described
below.
Rest: 3,6,9 seconds (average of 6)
Stimulus: 3 seconds
Anticipation: 3 seconds
Fedback: 3 seconds
Feedback contains several outcomes, events that are modeled as Win, NoWin,
Loss and NoLoss. In addition, the paradigm we are trying to replicate
compares each one of the four conditions to the "Rest" period. From what
you've described, their contrasts would be as follows
Win NoWin Loss NoLoss Rest
"Win" = Win-Rest 1 -1
"NoWin" = NoWin-Rest 1 -1
"Loss" = Loss-Rest 1 -1
"NoLoss" = NoLoss-Rest 1 -1
On top of that, there is an additional contrast, which is defined as
("Win" - "NoWin") - ("NoLoss" - "Loss"). For this contrast, I would think
the contrast would be defined as
Win NoWin Loss NoLoss Rest
1 -1 1 -1 0
This is a much more complicated design. So will the Rest period completely
cancel out? Or is there a different model to it?
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Going back to the original contrasts, I am still confused on the actual
meaning of what you said. I took a look at the contrasts you suggested.
Suppose I consider the "Context vs Rest" and "NoContext vs. Rest" contrasts,
which would be
1 0 (context > 0)
-1 0 (context < 0)
My understanding is that it is comparing times when the "Context" stimulus
is on with times when the "Context" stimulus is not on. The latter includes
true rest period and the "NoContext" stimulus period. If there is
significant activation in the "NoContext" stimulus period compared to the
true rest period, won't the signals get averaged out during the subtraction
causing a bias?
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