Please see inline responses below.
On Tue, Oct 16, 2012 at 2:22 PM, Annchen Knodt <[log in to unmask]> wrote:
> Hello All,
>
> I would like to model a physio-physiological interaction in SPM 8
> (interaction of time series from 2 separate ROIS), however I would like to
> determine if that interaction is dependent on the psychological condition
> determined by the experimental design. Stated differently, I want to test if
> the physio-physiological interaction during condition A is significantly
> different than the same interaction in condition B. My first concern is to
> make sure I am modeling this question properly. The second issue regards
> implementation.
>
> 1) If I understand the SPM8 manual properly, in order to test this
> question I should enter the following predictors into the design matrix: 1)
> a regressor representing the convolved time series from ROI 1; 2) a
> regressor representing the convolved time series from ROI 2; 3) a condition
> representing the experimental design; 4) a regressor representing the
> convolved time series from ROI 1 multiplied by the experimental design; 5) a
> regressor representing the convolved time series from ROI 2 multiplied by
> the experimental design; 6) a regressor representing the convolved time
> series from ROI 1 multiplied by the convolved time series from ROI 2; 7) a
> regressor representing the convolved time series from ROI 1 multiplied by
> the convolved time series from ROI 2 and the experimental design (the three
> way interaction term).
>
> Is this correct?
>>> Almost. You want the following regressors:
(1) timeseries from ROI1 (BOLD signal extracted from the ROI)
(2) timeseries from ROI2 (BOLD signal extracted from the ROI)
(3) Your task design matrix (one column for each task)
(4) the convolution of (the deconvolved timeseries in ROI1 * task) -->
1 column for each task
(5) the convolution of (the deconvolved timeseries in ROI2 * task) -->
1 column for each task
(6) the convolution of (the deconvolved timeseries in ROI1 * the
deconvolved timeseries in ROI2)
(7) the convolution of (the deconvolved timeseries in ROI1 * the
deconvolved timeseries in ROI2 * task) --> one column for each task
This can be done automatically with the gPPI toolbox; however, nothing
has been published on the three-way interaction as far as I know. I
also think you will need a number of trials in your task to get the
models to estimate the effects accurately to avoid collinearity in
your design.
>
> 2) Finally, does anyone know if this can be implemented in SPM8 using
> the Batch function? Additionally any other advice about implementation would
> be appreciated.
Use the gPPI toolbox available through NITRC (www.nitrc.org/projects/gppi)
>
> Thanks in advance for any help.
>
>
> Annchen Knodt
>
>
> ~~~~~~~~~~~~
> Annchen Knodt, M.S.
> Research Associate
> Laboratory of Neurogenetics
> 919.684.1039
> Duke University
>
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