Hello, I am struggling to set up my analysis for a face viewing fmri study.
In this block-design experiment, we had 13 blocks lasting 24 seconds as
follows:
fixation 24
fear 24
neutral 24
fixation 24
fear 24
neutral 24
fixation 24
fear 24
neutral 24
fixation 24
fear 24
neutral 24
fixation 24
I am trying to figure out how to best set up the first level analysis. I
initially tried to enter each condition as a separate EV, assigning 1 to
the blocks for that EV and 0 to all others. This led to an error, I bleieve
because I have 3 items instead of 2. (The error goes away when I only
include 2 EVs).
I then tried using the 3 column format to incorporate all conditions into
one EV, in which I assigned fear=1, neutral=-1, and fixation=0, similar to
that described in the frequently asked questions
(http://www.fmrib.ox.ac.uk/Members/joreilly/frequently-asked-questions-ppi).
Here is how my 3 column ev looked:
0 24 0
24 24 1
48 24 -1
72 24 0
96 24 1
120 24 -1
144 24 0
168 24 1
192 24 -1
216 24 0
240 24 1
264 24 -1
288 24 0
The problem is that this makes a wave form where BOLD is highest for fear
and lowest for neutral, and fixation is in the middle. So I haven't taken
fixation out of the model, it's being considered a middle-of the road
activator which I don't want. Could you advise me on how to set up my
analysis?
Thanks, Katie
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