I have a question. I will start with explaining what I have and what I
know and then follow with what I would like to know.
First:
The fmri experiment consists of simple on-off paradigms.
off (32s) on (32s) off(32s) on(32s) off(32s)
We are using SPM99b.
Second:
The design matrix can be modelled with this session containing one
or two conditions. I realize that modelling on and off seperately is
redundant, and the degrees of freedom are slightly different between the
two models.
I accept that the following is true:
One session
one condition model with a contrast=[1] is equal to two condition
model with a contrast=[-1 1] (-1 -> off and 1 -> on).
likewise [-1] is equal to [1 -1].
Two sessions
(each with the above on-off paradigm) I accept the following to
be true:
one condition model with a contrast=[-1 1] is the same as the two
condition model with contrast=[1 -1 -1 1] ( 1 -> session1 off, -1
->session1 on, -1 -> session2 off, 1 -> session2 on)
Third
My question.
With one session, on and off modelled as seperate conditions, what
does the contrast=[0 1] (0-> off, 1-> on) show?
Also with two sessions, on and off modelled as seperate conditions
what doe sthe contrast=[0 -1 0 1] (0 ->session1 off, -1 ->session1 on, 0
->session2 off, 1 ->session2 on) show?
I hope that I explained myself well,
Thank you,
Jason.
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