Yes that makes complete sense. However, it does not work for how I've
set up my contrasts and the effects I'm looking for - are there any
other ways?
Thanks!!
Eugene Duff wrote:
> If you want to limit you results to regions where, say, the first
> regressor was associated with a positive response, you can use
> contrast masking.
> Select contrast masking in the post-stats section and input the
> contrast where you tested for a positive response in that condition
> (e.g. the 1 0 contrast). Selecting "Mask using z>0.. " makes the
> masking less severe, showing regions where the fit of the regressor
> was positive, but not necessarily significant.
> I hope that makes some sense!
> Eugene
>
> 2009/5/18 Vina Goghari <[log in to unmask] <mailto:[log in to unmask]>>
>
> Thanks for your response. What is the way to ask for activations > 0?
>
> Thanks!
>
> tEugene Duff wrote:
>
> Hi Vina,
>
> 2009/5/18 Vina Goghari <[log in to unmask]
> <mailto:[log in to unmask]> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>>>
>
>
> Hi,
> A couple of quick questions about when setting up contrasts:
>
> (1) If you have two regressors that at a lower level you
> set up:
> R1 0 1
> R2 1 0
>
> And then you contrast: -1 1. Do you still have to be
> worried that
> the contrast could stem from a difference that is below
> zero for
> both regressors?
>
> If I understand you correctly, then yes, this contrasts would
> identify differences in responses even if they are all
> negative responses (deactivations).
> (2) When you have three groups can you set up your higher level
> contrast this way to sum 0 (1 1 -2)?
>
> This contrast will find regions where the responses modelled
> by the first two evs are significantly greater than those
> modelled by the third EV. These regions may not necessarily
> remain signficant when only one of the first two evs is
> contrasted with the third.
> Best
> Eugene
>
> Thanks!
>
>
>
>
> --
>
> Eugene Duff
>
> FMRIB Centre,
> University of Oxford
> John Radcliffe Hospital, Headington OX3 9DU Oxford UK
>
> Ph: +44 (0) 1865 222 739 Fax: +44 (0) 1865 222 717
>
> --
>
>
>
>
> --
>
> Eugene Duff
>
> FMRIB Centre,
> University of Oxford
> John Radcliffe Hospital, Headington OX3 9DU Oxford UK
>
> Ph: +44 (0) 1865 222 739 Fax: +44 (0) 1865 222 717
>
> --
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