Dear Haiteng,
The first thing I'd try is to compare the conditions directly without
subtracting anything. You can gain higher statistical power by putting
all your conditions in the same design (you can also put the control
conditions there) and doing your comparisons as contrasts in that
design.
If you are doing a paired t-test then subtracting the control
condition won't have any effect because it'll cancel out later anyway.
Vladimir
2010/4/6 Haiteng Jiang <[log in to unmask]>:
> Dear SPMers
> I am working with sources reconstruction on MEG evoked fields and have
> converted the results into images.I have some questions to improve my study.
> I am working on a paradigm with 5 conditions(4 experimental conditions and 1
> control condition) and would like to compare the sources creating the evoked
> fields.
> I have two possibilities:
> 1) first subtract control condition images from each experimental condition
> and then run 2 sample t-test.
> 2) first substract baseline images (pre -100ms-0ms) of all five
> conditons,then subtract 'pure' control condition images from each 'pure'
> experimental condition and at last run 2 sample t-test.
> I wonder which approach is more accurate in terms of extracting active brain
> areas?
> Thanks very much for your help!
>
> --
> Haiteng Jiang
> Brain Imaging Lab
> Research Center for Learning Science,
> Southeast University
> 2 Si Pai Lou , Nanjing, 210096, P.R.China
> Email: [log in to unmask]
>
>
>
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