Hi
It's identical, see the wiki description of GS, i.e. when using GS on
two vectors v1 and v2, the new vectors are v1 and v2-proj(v1,v2)
That is, you create the second vector by removing any correlation with
the first.
And yes, you don;t want to fully orthogonalise everything with
everythinge else - in fact if you simply add the nuisance regressors
then things will already be taken of.
hth
Christian
On 13 Aug 2009, at 17:22, Tal Herbsman wrote:
> A couple of of further questions, please forgive the ignorance/
> confusion, it's been a while
> since linear algebra:
>
> My understanding is that the GS de gives an orthonormal basis for
> the function space. It's
> not intuitively clear to me that this the same thing as covarying
> nuisance signals out of a
> time series.
>
> My application is not VBM whole brain correlation but rather a set
> of n ROI based
> timeseries cross-correlated with each other. Would GS decomposition
> of [ROI1 ... ROIn
> Nuisance1 ... NuisanceM] not ensure that I get no cross correlation
> (as opposed to cross
> correlating each ROI decomposed with only the nuisance variables?
>
> Tal.
>
> On Thu, 13 Aug 2009 10:25:22 +0100, Christian F. Beckmann
> <[log in to unmask]> wrote:
>
>> Hi
>>
>> Yes, the description of the method is very inclusive. Only issue I
>> have is that I'd advice using the Eigen-timeseries rather than the
>> mean timeseries within the ROIs for further analysis
>> hth
>> Christian
>>
>>
>>
>> On 13 Aug 2009, at 04:02, Xue, Feng wrote:
>>
>>> Here is an good example for ROI time series data correlation in RS-
>>> fMRI:
>>>
>>> "Mapping the functional connectivity of anterior cingulate cortex"
>>> by Daniel S. Marguliesa, A.M. Clare Kellya, Lucina Q. Uddina, Bharat
>>> B. Biswalb, F. Xavier Castellanosa, c, , and Michael P. Milham
>>> NeuroImage
>>> Volume 37, Issue 2, 15 August 2007, Pages 579-588
>>>
>>> On Thu, Aug 13, 2009 at 12:19 AM, Tal Herbsman<[log in to unmask]>
>>> wrote:
>>>> Dear FSL users, I would appreciate some advice on this: I am
>>>> interested in doing
>>>> correlation analysis on time series data extracted w/ fslmeants of
>>>> various anatomical
>>>> ROIs from FEAT preprocessed fMRI data. I have a set of nuisance
>>>> time series (CSF, WM
>>>> and whole brain global drifts). What would be the correct way of
>>>> regressing these
>>>> nuisance covariates out of my time series? I can think of two ways
>>>> but am not sure which
>>>> (if any) is correct, nor how to implement them:
>>>>
>>>> 1. orthogonalize the ROI time series with respect to global drift
>>>> time series. Is the FSL
>>>> orthogonalization available as a separate command line program?
>>>>
>>>> 2. use GLM to figure out PEs for nuisance regressors and subtract
>>>> from signal. Not sure
>>>> how to go about doing this.
>>>>
>>>> Any ideas?
>>>>
>>>> Tal.
>>>>
>>>>
>>>> Tal Herbsman, MD
>>>>
>>>> Assistant Professor
>>>> Department of Psychiatry
>>>> University of Wisconsin School of Medicine and Public Health
>>>> 6001 Research Park Blvd.
>>>> Madison, WI 53719-1176
>>>>
>>>> Office: (608) 263-6100
>>>> Fax: (608) 263-0265
>>>> [log in to unmask]
>>>>
>>>>
>>>
>>>
>>>
>>> --
>>> Best Regards
>>>
>>>
>>> National Key Laboratory of Cognitive Neuroscience and Learning
>>> Beijing Normal University
>>> Beijing, China. 100875
>>> Tel: +86-13810154455
>>> web: http://psychbrain.bnu.edu.cn
>>> ==============================================
>>> Welcome to MuDuo JinSheng BBS @ Beijing Normal University
>>> telnet://bbs.mdjs.org
>>> http://bbs.mdjs.org
>>
>> _______________________________________________
>> Christian F. Beckmann, DPhil
>> Senior Lecturer, Clinical Neuroscience Department
>> Division of Neuroscience and Mental Health
>> Imperial College London, Hammersmith Campus
>> Rm 419, Burlington Danes Bldg, Du Cane Road, London W12 0NN, UK
>> Tel.: +44 (0)20 7594 6685 --- Fax: +44 (0)20 7594 6548
>> Email: [log in to unmask]
>> http://www.imperial.ac.uk/medicine/people/c.beckmann/
>>
>> Senior Research Fellow, FMRIB Centre
>> University of Oxford
>> JR Hospital - Oxford OX3 9DU
>> Tel.: +44 (0)1865 222551 --- Fax: +44 (0)1865 222717
>> Email: [log in to unmask]
>> http://www.fmrib.ox.ac.uk/~beckmann
_______________________________________________
Christian F. Beckmann, DPhil
Senior Lecturer, Clinical Neuroscience Department
Division of Neuroscience and Mental Health
Imperial College London, Hammersmith Campus
Rm 419, Burlington Danes Bldg, Du Cane Road, London W12 0NN, UK
Tel.: +44 (0)20 7594 6685 --- Fax: +44 (0)20 7594 6548
Email: [log in to unmask]
http://www.imperial.ac.uk/medicine/people/c.beckmann/
Senior Research Fellow, FMRIB Centre
University of Oxford
JR Hospital - Oxford OX3 9DU
Tel.: +44 (0)1865 222551 --- Fax: +44 (0)1865 222717
Email: [log in to unmask]
http://www.fmrib.ox.ac.uk/~beckmann
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