Dear Li/Mike:
At 06:52 AM 4/27/2005, you wrote:
>Dear Darren Gitelman:
>
> I don't really understand "combine into one session". Since sessions
> are determined when the exp.
>conducted, how could i combine them after the exp?? Do you mean build
>sessions in one fMRI model?
Sorry I wasn't clearer. Yes what you have above is exactly right. Rather
than modeling the experiment as different sessions, model them as if there
was one long session. You will have conditions for A, B, C, and D that span
both sessions. Be careful when you set up the onset/duration vectors not to
extend the last block of session 1 right to the end, since convolution will
then make it trail off into session 2, which is not correct. In addition,
you should include as user defined vectors columns of ones corresponding to
each session effect. For example if we had 4 scans in each session these
vectors would be
1 0
1 0
1 0
1 0
0 1
0 1
0 1
0 1
The second column above is probably redundant (by the way) since it would
be modeled by the session one effect and the mean column at the end of the
design. In any case I have never seen this make any great difference in the
stat results- whether you include these columns or not, but perhaps this is
because I'm careful with the onsets. The t-values at the individual may
drop by a few hundredths since you use up a degree of freedom. In addition,
the results from this method and the individual session method are usually
very close. Once you set up the design this way It's easy to extract the
data and setup the driving and modulatory inputs for DCM.
Darren
>--- Darren Gitelman <[log in to unmask]>
>wrote:
> > Dear Li:
> >
> >
> > At 03:41 AM 4/26/2005, Li Bei wrote:
> > >Dear Darren Gitelman:
> > >
> > > I have some questions about DCM:
> > >
> > > Now i have 1 subject and 2 sessions(C for
> > >Control),
> > > Session1 : ACBCACBC
> > > Session1 : ACDCACDC
> >
> > I assume you mean Session1: ACBCACBC
> > Session2: ACDCACDC
> >
> > > 1,Now i want to build a DCM model with stimuli
> > >A,B,D. Is this possible? if yes, can you tell me
> > how
> > >to define VOI?
> >
> > DCM requires that the sessions be combined into one
> > session. This is also
> > necessary for extracting the VOI for DCM.
> >
> > > 2,Can i use VOIs exported from different
> > sessions
> > >to compose a DCM model??
> >
> > No. you need to combine into one session in your
> > design.
> >
> > Darren
> >
> >
> > > Thank you very much!
> > >
> > >
> > >Li Bei
> > >
> > >
> > >
> > >
> > >Bei Li
> > >Institute of Neuroinformatics
> > >Dalian University of Technology
> > >2 Ling Gong Rd, Dalian 116023, China
> > >Email:[log in to unmask]
> > >
> >
> >_________________________________________________________
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> >
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> >
> >
> >
>-------------------------------------------------------------------------
> > Darren R. Gitelman, M.D.
> > Cognitive Neurology and Alzheimer箂 Disease Center
> > Northwestern Univ., 320 E. Superior St., Searle
> > 11-470, Chicago, IL 60611
> > Voice: (312) 908-9023 Fax: (312) 908-8789
> >
>-------------------------------------------------------------------------
> >
> >
>
>Bei Li
>Institute of Neuroinformatics
>Dalian University of Technology
>2 Ling Gong Rd, Dalian 116023, China
>Email:[log in to unmask]
>
>_________________________________________________________
>Do You Yahoo!?
>注册世界一流品质的雅虎免费电邮
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-------------------------------------------------------------------------
Darren R. Gitelman, M.D.
Cognitive Neurology and Alzheimer箂 Disease Center
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
Voice: (312) 908-9023 Fax: (312) 908-8789
-------------------------------------------------------------------------
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