Hi,
I understand the temptation but please don't. Running a FX analysis is effectively like concatenating when getting it right (i.e. as if there were no issues wrt voxel-wise means and shifts thereof). If you try to do this explicitly with fslmerge then you will enter additional bits of variability in the data (e.g. as now the pre-processing will not work well) and therefore you will likely reduce sensitivity to detecting an effect.
hth
Christian
On 16 Mar 2011, at 22:06, Lara Foland-Ross wrote:
> Hi there,
>
> I am running an fmri experiment in which each subject has 3 separate fmri scan sessions. Each scan session has unique timing/stimuli onsets.
>
> To combine intra-subject runs, what I've done in the past is:
>
> 1. Analyze each session separately for each subject (including registration).
> 2. Use a higher-level analysis to combine a subject’s sessions. I've done this using the fixed-effects stats option, selecting GROUP MEAN model (single EV, with all 1’s in that EV and a single contrast with a single “1” in it), making sure that inputs are lower level FEAT’s.
> 3. Once I have #1 and #2 completed for each subject, I then run a separate higher-level analysis to look at effects at the group level. For this, I select the option “Inputs are 3D cope images” in the “Data” tab. For the input, I select the [subject].gfeat/cope[n].feat/stats/cope1 image. The rest of the higher-level settings I leave as normal...
>
> But now I'm wondering if I can simply combine multiple scan runs for each subject by concatenating the niftii files for the 3 scan sessions? That is, can I just use the "fslmerge" utility to concatenate session 1's niftii file with session 2's and session 3's? This way, I will have only on lower-level analysis for each subject.
>
> Please let me know if this is possible.
>
> Many thanks for your expert advice in advance,
> Lara
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