help
help > RE: Task conditions to include in gPPI model
Oct 20, 2021 10:10 PM | Alfonso Nieto-Castanon - Boston University
RE: Task conditions to include in gPPI model
Dear Lillian,
In gPPI analyses the effect-of-interest (the measures that you are computing separately for each subject and each condition and taking to your second-level analyses) characterize the unique increase/decrease in connectivity associated with each individual condition (only computed for those conditions entered in the model) when compared to the implicit baseline/reference connectivity (covering everything else that is not explicitly entered into the gPPI model). In this case I would probably recommend not including the "instruction period" condition in your gPPI analyses, unless of course you would prefer to explicitly control for potential connectivity differences between the "instruction period" and the "fixation" conditions. When not including "instruction period", you will get five connectivity measures (one for each of the four "tasks" and another for "fixation"; all of the individually represented with respect to the same baseline) and then you should define the appropriate contrasts (e.g. taskA - fixation, or taskA - taskB) in your second-level analyses (and you could also perhaps look there at the individual "fixation" effect to evaluate whether that was different from the common "instruction period" implicit baseline).
Hope this helps
Alfonso
Originally posted by omaomae:
In gPPI analyses the effect-of-interest (the measures that you are computing separately for each subject and each condition and taking to your second-level analyses) characterize the unique increase/decrease in connectivity associated with each individual condition (only computed for those conditions entered in the model) when compared to the implicit baseline/reference connectivity (covering everything else that is not explicitly entered into the gPPI model). In this case I would probably recommend not including the "instruction period" condition in your gPPI analyses, unless of course you would prefer to explicitly control for potential connectivity differences between the "instruction period" and the "fixation" conditions. When not including "instruction period", you will get five connectivity measures (one for each of the four "tasks" and another for "fixation"; all of the individually represented with respect to the same baseline) and then you should define the appropriate contrasts (e.g. taskA - fixation, or taskA - taskB) in your second-level analyses (and you could also perhaps look there at the individual "fixation" effect to evaluate whether that was different from the common "instruction period" implicit baseline).
Hope this helps
Alfonso
Originally posted by omaomae:
Dear CONN community,
I am still trying to fully understand how gPPI task-based connectivity analyses work. While CONN's GUI instructions mention only including task conditions of interest when creating the gPPI model in the first level analyses, I do not understand the significance of including conditions of non-interest (that don't relate to a baseline condition) in the model or not.
To be specific, my event-related experiment has three conditions imported from SPM.mat files: task stimulus conditions (which are actually 4 different kinds of conditions that I merged into one for CONN), fixation, and instruction periods. My conditions of interest would be the stimulus conditions and fixation (as an explicit baseline). My question is whether I should include the "instruction period" condition in the gPPI model or not, and how I should properly interpret the different result I get if I include or exclude it.
Thank you,
Lillian
I am still trying to fully understand how gPPI task-based connectivity analyses work. While CONN's GUI instructions mention only including task conditions of interest when creating the gPPI model in the first level analyses, I do not understand the significance of including conditions of non-interest (that don't relate to a baseline condition) in the model or not.
To be specific, my event-related experiment has three conditions imported from SPM.mat files: task stimulus conditions (which are actually 4 different kinds of conditions that I merged into one for CONN), fixation, and instruction periods. My conditions of interest would be the stimulus conditions and fixation (as an explicit baseline). My question is whether I should include the "instruction period" condition in the gPPI model or not, and how I should properly interpret the different result I get if I include or exclude it.
Thank you,
Lillian
Threaded View
| Title | Author | Date |
|---|---|---|
| omaomae | Oct 20, 2021 | |
| Alfonso Nieto-Castanon | Oct 20, 2021 | |
| omaomae | Oct 21, 2021 | |
| Alfonso Nieto-Castanon | Oct 21, 2021 | |