Answer 1:
spmT images are T-statistics. They are not normally distributed and
thus are not suitable for use in parametric statistics such as
one-sample t-tests, two-sample t-tests, ANOVAs, etc.
con images should follow a normal distribution.
Thus, only con images should be used at the second level since the
assumption is that the errors are normally distributed. In a
one-sample t-test, the error distribution follows the distribution of
the dependent variable. Thus, non-normal distributions (e.g. T-tests)
will violate the assumption that the data is normally distributed.
Answer 2:
One could convert the spmT to and spmZ map and then use it as in done
in resting state analysis; however, the interpretation is then
different.
Interpretation of con images: The BOLD response is significantly
different from zero (or between A and B).
Interpretation of Z images: The significance of the BOLD response is
significantly different from zero (or between A and B).
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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On Wed, Aug 31, 2011 at 10:26 AM, Vladimir Bogdanov <[log in to unmask]> wrote:
> Dear SPM experts,
>
> Why in the second level of analysis in SPM the con images are used but not spmT images? I am a biologist and not an expert in statistics, thus I need a simplified explanation, if possible.
>
> Thank you in advance for your responses!
>
> Sincerely yours,
> Vladimir
>
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