You want to adjust the data to remove non-neuronal sources in the BOLD signal. SPM does this by using the F-contrast across your conditions of interest and then removing the null-space.

The f-contrast should include ALL conditions, not the ones for the comparison with PPI or DCM and should the f-contrast testing whether any condition is different than 0.
For 2 conditions: [1 0; 0 1]
For 3 conditions: [1 0 0; 0 1 0; 0 0 1]
etc.


Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Mon, Dec 16, 2013 at 11:51 AM, André Schmidt <[log in to unmask]> wrote:
Dear list,

I intend to extract time series from my VOI's for later DCMs (obtained from a t-test, i.e emotional greater than neutral material). In several papers, they often use an appropriate F-contrast and adjust it for eigenvariate extraction (by the effect of interest) - how can I adjust the emotional vs neutral t contrast (if needed)?

In general, should one use t or F contrasts for time series extraction and is adjusting always recommended?

Many thanks for your help
AS