Dear SPMers,
I have some questions about stimulus duration and contrasts
The first question is that when I set an event-related model using the
hrf with derivatives, what is the meaning of the stimulus-duration?
Based on SPM manual, durations should be 0 for event-related design.
But I'm confusing.
For example, it would be reasonable for simple tasks (ie, perceptual
or attention tasks), but I'm not sure whether or not I have to use
stimulus duration for complex tasks (ie, WM task using four letters
and locations).
In my thought, if I enter 2, for example, for the durations, it would
be sensitive to detect BOLD, but It cannot be interpreted as a pure
BOLD estimation. Is this correct?
The second question is that if I have 3 conditions including two
experimental (let's say A and B) and a control conditions, the t-maps
for all conditions would be calculated by using simple t-test at the
individual analysis. And then, I can specify "A>control" and
"B>control" at the group level.
But, in different way, I can make "A>control" and "B>control" using
two-sample t-test at the individual level then I can run simple t-test
for "A>B" or "B>A" as well as "A>control" and "B>control".
In other words, at the following table,
the first way the second way
1st level A, B & control (simple t-test) [A>control] & [B>control]
2nd level A>control & B>control [(A>control)>0],
[(B>control)>0], [A>B] & [B>A]
[A>control] in the first way and [(A>control)>0] are same?
I appreciate your help in advance.
Sincerely,
Chobok
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Chobok Kim
e-mail: [log in to unmask]
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