Hi,
I'm a little confused as to what the controls group is for - what's
the difference between controls and group2-pre ? Isn't the main
contrast of interest just a paired t-test in group 2 post-pre?
Cheers.
On 9 Mar 2009, at 09:54, Rebecca wrote:
> Dear All,
>
> I am having some difficulties with my analyses and was wondering if
> anybody
> could offer some advice or reassurance, as I am a newcomer to fMRI
> analysis
> of any kind.
> I have read both the FEAT manual and other posts from the archives,
> but still
> remain confused.
>
> I have two groups:
> Group1 = controls (scanned once)
> Group2 = experimental group (scanned pre and post training).
>
> My paradigm was separated into 2 consecutive sessions which I have
> separately analysed at first level and then combined using a fixed
> effects
> higher level analysis.
>
> For between group analysis, for the main effects I have performed Two-
> sample unpaired T-Tests for my Controls vs Pre and then again for my
> Controls vs Post.
> I have them performed a Repeated Measures analysis on the Pre vs
> Post data.
> Is this correct?
>
> I now want to look at contrasts between my groups and it is here
> that I am
> getting really confused. I understand that I have to use contrast
> masking to
> allow for better interpretation of my findings, but remain unsure
> about how to
> do this.
>
> For example I want to look at Pre (Left > Right) Vs Post (Left >
> Right). I
> therefore want to know where the Pre group had greater activation
> than the
> post group when looking at Left vs Right. However, my analyses are
> being
> performed on cope files from my second level g.feat directories and
> therefore
> only contain the (left vs right) data and not the left data and the
> right data
> separately.
>
> Therefore what do I use to contrast the analysis with? And do I
> contrast Left
>> Right only with Left, and my Right > Left analysis only with right,
>> or do I
> have to contrast both???
>
> Sorry if these seem like basic questions, but any advice will be
> appreciated.
> Please keep responses as basic as possible :)
> Thanks Again
>
> Rebecca
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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