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Chris,

You might want to consider using FIR modeling, then you could have a 2xN ANOVA and you could do post-hoc tests at each timepoint after the block begins.

Alternatively, have you considered that this finding is what Steve Petersen's group has reported (e.g. dual network approach to top-down control) or block transients (Fox et al. 2005)? You could try modelling an instantaneous event and a block duration event and compare the responses of these two timecourses in ROI analyses. This could be a bit better as you have a reason to look at the 2 elements of the task. Using 3 time periods is not really an objective way to capture the response unless you think the first part lasts for 6 seconds.


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 Tue, Jul 16, 2013 at 4:41 AM, Paret, Christian <[log in to unmask]> wrote:

Hi,

 

I have a  design including several conditions with 18 seconds blocks of stimulus presentation. In one condition, we observed differential BOLD signal time courses in 2 ROIs which we’d like to corroborate by post-hoc  tests. In detail, we observed one region with a response at the onset of the trial and a quick decrease to baseline, while the other ROI activates throughout the duration of stimulus presentation. We want to do a post-hoc statistical test showing an interaction of time courses between these ROIs.

 

A first idea was to model each trial as three conditions comprising the thirds of the trial duration (i.e. 1:6,7:12,13:18) and calculate a factorial analysis with spm. Another idea is to do a split of trials as indicated above and build the area under the curve of the single-subject time courses (and calculate a 2x3 ANOVA).

 

I’m not sure whether the first approach would be a valid statistical test and whether there would be other ideas more suited to solve my problem.

 

Appreciate your help!

 

Chris