Dear Kathleen,
This is just a GUI display thing - you can verify the content of the
contrast vector by double-clicking on the plot; it will be displayed in
the MATLAB window.
Otherwise, 8 subjects only? What about using the one-way anova within
subject option? Main effect of time will be an F-contrast [1 -1 0 0 0
0;0 1 -1 0 0 0;0 0 1 -1 0 0;0 0 0 1 -1 0;0 0 0 0 1 -1].
Best regards,
Guillaume.
On 10/04/18 17:26, Hupfeld,Kathleen E wrote:
> Dear SPM experts,
>
>
> I had a question about contrast values. Here, I just want to see whether
> there is a main effect of a task across six time points. I want to look
> at both the positive (+1; "activation") and negative
> (-1; "deactivation") contrasts here. I have three people who are missing
> the sixth time point.
>
>
> In contrast manager, when I enter six _*+1's*_ (for each time point), it
> looks like this; in the contrast(s) display on the right, it looks like
> I have entered a negative number?
>
>
>
> When I enter all _*-1's*_, it looks like this; in the contrast(s)
> display on the right, it looks like I have entered a positive number?
>
>
>
> However, if I exclude, for instance, the first time point, and enter 0 1
> 1 1 1 1, the positive contrast with five +1's looks positive:
>
>
>
> and the negative contrast with five -1's looks negative:
>
>
>
> _*So, my two questions are*_:
>
> 1) Am I doing something wrong here? Either is it inappropriate to run
> the [1 1 1 1 1 1] and [-1 -1 -1 -1 -1 -1] contrasts, or am I entering
> them incorrectly?
>
>
> 2) --or rather, is the way the contrasts display on the right-hand side
> of Contrast Manager just a facet of how the GUI works, and I am doing
> this correctly/it is testing the appropriate contrasts?
>
>
> Best regards,
> Kathleen
>
>
> Kathleen Hupfeld
>
> PhD Student, Biobehavioral Science
> Neuromotor Behavior Lab
> Department of Applied Physiology & Kinesiology
> University of Florida
> 80 Florida Gym | 1864 Stadium Rd.
> Gainesville, FL 32611
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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