Hi Kent,
Thanks for the advice about modelling sessions separately.
Regarding the realignment procedure, I'm not sure I understand why it's
better to realign each session separately compared with realigning the
images as if they all came from a single long session. In either case,
aren't all of the images just realigned to the first image acquired?
Thanks,
Daniel Weissman
> Hi Daniel,
> I would tend to enter each session separately and not to concatenate
> into one long session per subject.
> I can think of a few reasons for this, primarily b/c the event-related
> response do not overlap across sessions. Using this procedure one can still
> create a subject specific contrast for random effects analyses. I would use
> the default settings for the high pass filter. Low pass filtering is a
> little different story - I believe it is recommended to use the hrf, but we
> typically filter our data outside spm b/c we (and others) have noticed high
> frequency noise can be prevalent in some scanners. I also would realign
> each of the sessions separately.
> Other groups may have different opinions.
>
> Best regards,
> Kent
> ______________________________
> Kent A. Kiehl, Ph.D.
> 2255 Wesbrook Mall
> Departments of Psychology and Psychiatry
> University of British Columbia
> Vancouver, B.C., Canada, V6T 2A1
> http://www.psychiatry.ubc.ca/sz/nilab/personnel/kiehl/
> Office 604-822-0777; Lab 604-822-7128; Fax: 604-822-7756
>
> ----- Original Message -----
> From: Daniel Weissman <[log in to unmask]>
> To: spm <[log in to unmask]>
> Cc: <[log in to unmask]>
> Sent: Monday, March 13, 2000 12:30 PM
> Subject: Number of Sessions per subject
>
>
> > Hi,
> > I've just run an event-related fMRI study that in which I
> > collected 8 "blocks" of data for each subject. Each block was a 6-minute
> > long scan. I'm wondering whether it is better to enter each "block" as a
> > separate session in the analysis (i.e., 8 sessions per subject), or to
> > "pool" all 8 blocks from each subject into one huge session (i.e., one
> session
> > per subject).
> >
> > In the discussion list, some have recommended "pooling"
> > multiple sessions into one big session for each subject (9/22/98),
> > but others have argued that such pooling might not be a good idea
> > (10/15/99).
> >
> > I'd appreciate any advice and, if it is possible to perform the
> > analysis in both ways, I'd be interested to know whether and how the
> > high- and low-pass filters should be set in each case.
> >
> > Thanks,
> > Daniel Weissman
>
>
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