Dear Henry
In SPM96, there is a term "global normalization" in the statistical module.
Does this mean all the scans are intensity-scaled so that they have the
same average intensity in the image ( or imaged brain)?
I hope that the 'big brains' of SPM will check this response, but here is
what I had understood :
The answer is yes.
In SPM there is two way to avoid global intensity effect :
1- using the classical scaling : say that your first volume wil give the
gold-standard of global intensity, and all the others will be 'normalized'
to have the same global intensity.
2- Using the global intensity as a covariates of no interest (personally I
would prefer this as it counts this operation as loss of degree of liberty)
You wil find a much better explanation than this one by reading SPM course
if its not already done (in this case I apologize for having misunderstood
your question)
http://www.fil.ion.ucl.ac.uk/spm/course/notes97/Ch3.pdf
Is this scaling carried across different subjects?
I don't think so. Intersubject variations should be remouved by the subject
per subject covariate.
Your help will be highly appreciated.
Hope this could help
Best regards
Jack
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