On Tue, 29 Jul 2008 10:57:23 +0900, Woo-Suk, Tae <[log in to unmask]> wrote:
> Hi SPMers
> I am under analysis with auditory fMRI data.
> In my fMRI stim. paradigm, the number of the standard stim. was 3 times
larger than
> the number of deviant stim.
> In the 1st level analysis, I got the contrast images by regression
analyses with standard or
> deviant SOA, then tested the second level analysis (paired T between
deviant and standard)
> with con. images from the first level analysis.
> But, there was no activation of Heschl's gyrus, although there was greater
activation in the
> Heschl's gyrus with deviant stimulation.
> This result could come from unbalanced sample size of my fMRI study?
> If this result came from the sample size problem, how can I correct it?
The way you analyzed the data sounds odd.
I assume you had both standard and deviant stims in the same sessions. In
that case, you would contrast standard versus deviant __at the first level__
(the subject level).
Then you would carry the contrast "standard versus deviant" to the second
level. If you have only a single population (e.g., all healthy subjects),
you would perform a one-sample t-test. If you have two populations
(healthies and patients, for example; or, men and women; etc) you would
perform a two-sample t-test (_not_ paired).
From your description, however, it sounds like you created subject-level
contrasts for standard and deviant and brought _both_ of them to the second
level, and then subtracted them at the second level through the paired
t-test, which isn't the right way to go about it.
> Woo-Suk, Tae
> Chuncheon, Korea
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