LLN, le 20/03/07
Hi!
Here is what I suggest - if I got you correctly:
(1) tell SPM that your sessions are not replications and enter the
appropriate vector of onsets for each session/subject, then compute
all your 1-level contrasts (e.g., [cond1-cond2]) for each subject
individually,
(2) port the corresponding con_* files to 2-level analyses using:
- 1-sample t-tests with a contrast set at [1] if you wanna look at
each group separately;
- 2-sample t-tests with your two groups and contrasts set at [1 -1]
(or [-1 1] depending on what you're looking at).
(At this point, it does no longer matter if the onset vectors are
different across subjects.)
Another option is to use a two-factorial ANOVA (factors "group" and
"task", each with two levels), but I'm less familiar with this
approach and leave it to real experts to comment on it.
>only there is one task/condition in every sesson's design matrix)
What do you mean exactly? Pay attention to the fact that comparing
directly 2 conditions from 2 sessions is not recommended. Your onset
vector suggests that there are at least 2 conditions per session,
right? Perhaps, condition 1 vs. some baseline (fixation/rest)? If
this is what you have, simply set your first-level constrast to [1].
Hope this helps,
Mauro.
>Dear SPMers,
>recently, I encountered a problem: I want to do a group analysis on
>2 groups data, presumed as X group, has 10 sessions/subjects ,and Y
>group has 10 too. all the sessions have the same time points. it
>would be a simple question that can be deal with SPM/BASIC MODEL if
>the design paradigms(of each session) were identical. In fact, the
>design martrix of each session is not the same and irregular.(for
>examle, stimulus time of A1 is 5 55 100 136 158 190, and the A2 may
>be 10 75 120 160, only there is one task/condition in every sesson's
>design matrix). I don't know whether I can use SPM/BASIC MODEL to do
>group analysis. if not, anyone who can give me some advice? Thank
>you very much!
>
>Zhiqiang Zhang
>Lab. of functional Neuroimage
>Dept. of Med. Img., Jinling Hospital.
>Nanjing University, Nanjing, China.
>
>
>
><http://cn.mail.yahoo.com/> '-" -3.5Ge C20M
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Mauro PESENTI
Research Associate, National Fund for Scientific Research (Belgium)
Unite de Neurosciences Cognitives
Departement de Psychologie
Universite Catholique de Louvain
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