Thanks for your response. What is the way to ask for activations > 0 or
check for them?
Thanks!
tEugene Duff wrote:
> Hi Vina,
>
> 2009/5/18 Vina Goghari <[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
>
> --
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