Dear Kent,
I agree with your comments, and would also remind the list members of
the following paper:
P.M. Macey, K.E. Macey, R. Kumar, and R.M. Harper. A method for
removal of global effects from fMRI time series. NeuroImage 22 (2004)
360-366.
and code available from the archives:
http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind04&L=spm&P=R161460&I=-1
regards,
Greig
On 07/03/2005, at 10:58 AM, Kent A. Kiehl wrote:
> Dear fellow SPMers,
> I think it is useful from time-to-time to remind the list of
> the
> issues with 'within session' scaling, or proportional scaling (that
> pesky
> 'scale' button) in SPM2. I continue to feel that this issue is the
> single
> biggest problem in image analyses today. I continue to get papers and
> grants
> to review in which the users blindly use this 'feature'.
> I encourage those who wish to do use scaling to read the below
> papers (better now then when your grant is being reviewed).
> Note that this is different than the between session or the
> grand
> mean scaling in SPM2 - which is not prone to the issues outlined in the
> papers below. Best regards, Kent
>
> Aguirre, G. K., Zarahn, E., & D'Esposito, M. (1998). The inferential
> impact
> of global signal covariates in functional neuroimaging analyses.
> Neuroimage,
> 8(3), 302-306.
>
> Andersson, J. L. (1997). How to estimate global activity independent of
> changes in local activity. Neuroimage, 6(4), 237-244.
>
> Andersson, J. L., Ashburner, J., & Friston, K. (2001). A global
> estimator
> unbiased by local changes. Neuroimage, 13(6 Pt 1), 1193-1206.
>
> Desjardins, A. E., Kiehl, K. A., & Liddle, P. F. (2001). Removal of
> confounding effects of global signal in functional magnetic resonance
> imaging analyses. Neuroimage, 13, 751-758.
>
> ------------------------------------------------------
> Kent A. Kiehl, Ph.D., Director
> Clinical Cognitive Neuroscience Laboratory
> Olin Neuropsychiatry Research Center, Institute of Living
>
> Assistant Clinical Professor
> Department of Psychiatry
> Yale University School of Medicine
>
> Mailing address and contact information:
>
> Institute of Living
> 200 Retreat Avenue
> Olin Neuropsychiatry Research Center
> Hartford, CT USA 06106
> Tel: 860-545-7385; Fax: 860-545-7797
> Email [log in to unmask]
> http://www.nrc-iol.org/ccnlab
>
>
>
>
>
>
>
> -----Original Message-----
> From: Stephen J. Fromm [mailto:[log in to unmask]]
> Sent: Sunday, March 06, 2005 7:12 AM
> Subject: Re: Global scaling and grand mean
>
> On Sat, 5 Mar 2005 17:06:19 +0000, Joe Maisog <[log in to unmask]>
> wrote:
>
>>> A few years ago it was common for people to do global scaling
>>> in SPM fMRI analyses. Nowadays the advice is that, in most
>>> situations, it shouldn't be done.
>>
>> Does anybody out there still routinely perform global scaling on their
> fMRI
>> data? I am curious to see what the consensus is.
>>
>> Thanks very much!
>>
>> Joe
>
> I don't know what individual groups do, but the consensus among SPM
> folk
> seems to be not to do it.
>
> One notable exception is Keith Worsley.
>
> For people I know, the debate assumes that global scaling shouldn't be
> done, and the only question is whether to use grand mean scaling only,
> or
> to do "voxelwise scaling" so that effect sizes are in percent signal
> change.
>
>
__
Dr Greig de Zubicaray
ARC Research Fellow
Centre for Magnetic Resonance
University of Queensland, QLD 4072, Australia
Tel: (+617) 3365 4100 (Office) or (+617) 3365 4250 (Direct)
Fax: (+617) 3365 3833
http://www.cmr.uq.edu.au/CMR_Staff_Zubicaray.htm
***Please note change of location as of January 2005***
Room B106, Ritchie Building, Research Road
(across the road from CMR)
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