Hi
I am working on fMRI data of bilingual children. I want to do
comparisons between groups (one way anova's) Presently I am working
on a verb generation from a block design, 3 trials: drawings (1),
nonsense words (2), and verb generation from visual noun (3) .
contrast of interest here is (-1 0 1) on individual level.
I read that some people use a main effect mask when building the
model when performing group comparisons. Indeed it sounds clever to
only include differences in activation from the activations seen in
the overall group/ the task. Therefore, the idea is to produce the
effect of the whole group (bilingual and monolingual, L1 and L2,
...), which is then used as a "main effect" mask for later inter
group analysis.
So, I started playing around and found in the list that you can use
the con.img of the relevant contrast of all sessions, main effect, as
mask. although there is also a mask.img file or I could use the SPM_T
map and calculate (via Imcalc) for instance i1>3 to include only
areas with activations that are higher than 3
1- is it best to use the SPM_T map calculated at threshold >3 (for instance)?
2- can i use the con.img? because that are not 1 and 0 values but
numerical data, so what am I really doing then? (because it does work)
3- do i simply use the mask.img generated after performing the single
group analysis of all sessions? if yes, what is then the threshold
used to generate the mask.img? and can I change that and how?
4- all group comparisons are of course RFX analyses. should i use the
RFX 1 sampled T test of all sessions as base for main effect or can I
use the FXD analysis?
thanks very much for the help!!
Katrien
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Katrien Mondt
Prospective Research for Brussels
BHG - RBC
Vakgroep Taal- en Letterkunde
Faculteit Letteren & Wijsbegeerte
Vrije Universiteit Brussel
Pleinlaan 2
1050 Brussel
tel: 00 32 2 629 2668
fax: 00 32 2 629 3684
[log in to unmask]
www.vub.ac.be/DITO
www.vub.ac.be/SGER
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