help > RE: Contrasts selection for timeseries extraction
Feb 22, 2021  10:02 PM | Donald McLaren
RE: Contrasts selection for timeseries extraction
Hi Kitty,

In any PPI, you are extracting the timeseries for the entire functional run. The difference between different extractions is often how the timeseries is adjusted. In gPPI, it is recommended to only adjust for variables of no interest (e.g. motion parameters). To do this, one uses the omnibus F-contrast. P.Contrast='Omnibus F-test for PPI Analyses'. This is the default behavior.

The gPPI scripts will extract the timeseries and then generate the gPPI model for you. There is no need to extract the timeseries separately.

Originally posted by kitty zhu:
Dear gPPI experts,
I have some questions about the contrast selections for timeseries extraction before running the gPPI script.
In the sPPI tutorial(the attention example), they use the motion contrast (include attention and non-attention conditions) to extract timeseries for following attention-modulated connectivity analysis. In gPPI, all conditions and corresponding PPI items are modeled in the GLM, so I wondered whether I need to extract timeseries including all conditions in gPPI GLM model . For example, in above attention example, using function spm_region, I should extract timeseries from F contrast(1 0 0 ;0 1 0;0 0 1) incuding all conditions rather than just attention effect(0 -1 1) contrast, is that right?

kind regards,

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kitty zhu Feb 18, 2021
RE: Contrasts selection for timeseries extraction
Donald McLaren Feb 22, 2021
kitty zhu Feb 25, 2021