Hello I have just carried out my first fMRI study and am now in the process
of trying to analyse the data. However as I am new to fMRI and FSL and have
some questions I hoped someone could clarify.
1. I have a block design with 6 different conditions (doors, shapes, angry
face, fear face, neutral face and happy face blocks) – to represent this in
the model I have set up each of the conditions as a separate EV and used the
3 column option to specify the shape. In the 3 column timing files I have
put the onset time of the block, the duration of the block (i.e., 24 sec)
and a weight of 1 – I have done this for each of the EVs
i.e., 29.5 24 1
239 24 1
I am not quite sure how FSL interprets this as a block design given that my
design is not a simple ON/OFF design. The only difference I can see between
my timing files and those for an event related design is the block length.
Does this matter?
2. I am also not sure which convolution option to specify. I am thinking I
should go for the double gamma option as this would model a canonical HRF
but the fact that gamma is the default is making me have doubts. Any
suggestions?
3. When setting up my EVs is it the case the the positive and the negative
should equal 1? i.e.,
1 1 -1 -1 = wrong
0.5 0.5 -0.5 -0.5 = right
Thanks very much for any advice/suggestions in advance.
Jess
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