Dear David,
Thanks so much for your help. I was able to get the correct version to then
apply the correct "zeroing" options.
Would you mind telling me if my PPI set up is coorect: For EV1, I have the
task, set up as a 3 column entry, with 0 for fixation (baseline), 1 for
fear and -1 for neutral, to hopefully allow me to look at fear minus
neutral in this EV. For EV2, I have the timecourse. For EV3, I have the
interaction. I have no filtering on any of these EVs, but I do have the
task EV convolved with the "gamma" otpion. I have no additional EV
regressors (not sure what these would be for my study design), and for the
contrasts I have:
EV1 EV2 EV3
1 0 0
0 1 0
0 0 1
Should I be adding an additional regressor to take out the global signal?
Anything else I'm doing wrong here?
Thanks very much for your guidance in my probably very rudimentary
questions.
-Katie
On May 3 2010, David V. Smith wrote:
>Hi Kathryn,
>
> 1) Which version of FSL are you using? You should have three 'zeroing'
> options (min, centre, mean). They are not the same (see
> http://www.fmrib.ox.ac.uk/Members/joreilly/the-zero-ing-options-in-ppi).
> If your GUI display doesn't look like the ones on Jill O'Reilley's PPI
> pages, then you may need to grab the latest version of FSL.
>
> 2) Assuming you're just contrasting the face conditions and leaving the
> fixation unmodeled (it's your baseline, right?), then you should be able
> to combine the two regressors into one by putting 1s and -1s in the 3rd
> column of the regressor. See
> http://www.fmrib.ox.ac.uk/Members/joreilly/frequently-asked-questions-ppi
> for more information.
>
>Hope this helps,
>
>David
>
>
>
>On May 3, 2010, at 6:52 PM, Kathryn Cullen wrote:
>
>> Hello, I am trying out a PPI analysis using FEAT for the first time and
>> have run into 2 questions:
>>
>> (1) In the instructions that I have seen, there is an option for "make
>> zero" on the stats set up where you choose "interaction" for the 3rd EV,
>> but in my fsl gui there is only the option to check "demean". Is it OK
>> to check demean for both EV1 and EV2, and will it mean the same as
>> what's described in the on-line presentation (Centre for EV1 and mean
>> for EV2).
>>
>> (2) The task for this experiment involves 3 conditions, which are
>> viewing fixation, viewing neutral faces, and viewing fear faces. I'm not
>> sure how to set up the contrasts in FEAT since the examples are usually
>> for on-off paradigms. This is a problem that I also am running into as I
>> try to run the traditional analysis of activation between conditions and
>> between patient groups.
>>
>> Thanks, Katie
>>
>> Kathryn R. Cullen, M.D.
>> Assistant Professor
>> University of Minnesota Medical School
>> 2450 Riverside Avenue Minneapolis, MN 55454
>
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