Hello Anders,
The expression you wrote is correct to remove the variability of the data explained by the registration parameters.
However, removing the effect prior to the GLM analysis is not equivalent to include them into the design matrix along with the experimental regressors and fit this model.
All best,
Cesar
On Aug 12, 2010, at 10:40 AM, Anders Eklund wrote:
> Thanks for your reply, but I want to do it without SPM. I thus want to know how the registration parameters are used to remove effects of head movement. Right now I do it like this (not sure that this is correct), registration parameters = RP
>
> % Remove best fit of registration parameters (GLM approach)
> beta = inv(RP'*RP)*RP'*timeseries;
> e = timeseries - beta'*RP;
>
> % Perform GLM on e, instead of on timeseries
>
> Is this correct?
>
> I've read somewhere that the registration parameters can be put directly into the design matrix to do this. If my original contrast vector is [1 -1], what should the contrast vector look like if I add the registration parameters?
>
> /Anders
>
> 2010-08-12 10:11, Karsten Specht skrev:
>> Dear Anders,
>>
>>
>>> I'm working on a new approach to remove the effects of head movement>(especially head movement that is highly correlated with the stimulus>paradigm) that is not removed by the registration. I want to compare my>approach to the one that can be used in SPM, to add the registration>parameters as regressors. I'm however not sure exactly how this is done>and I want to implement it myself in Matlab. Can anyone tell me in which>SPM file (and which line) this is done? I use a simple fMRI experiment>with activity and rest.
>>>
>> That's not done automatically in SPM. During the (manual) model specification, you go to the option 'multiple regressors' in the "Subject/Session" branch and select the 'rp_***.txt' file from the respective image directory.
>>
>> Good luck,
>>
>> Karsten
>>
>> -- -------------------------------------------------------------
>> Karsten Specht, PhD
>> Department of Biological and Medical Psychology& National Competence Centre for functional MRI
>> University of Bergen
>> Jonas Lies vei 91
>> 5009 Bergen
>> Norway
>> Tel.: +47-555-86279
>> Fax: +47-555-89872
>> [log in to unmask]
>> http://fmri.uib.no/
>>
>
> --
> --
> -----------------------------------------------------------------------
>
> Anders Eklund
> Phd student
>
> Medical Informatics, Department of Biomedical Engineering
> CMIV, Center for Medical Image Science and Visualization
>
> Tel: +46 73 6003790 mail: [log in to unmask]
> Fax: +46 13 101902 web: http://www.wanderineconsulting.com/
> -----------------------------------------------------------------------
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