Dear Sun,
In the case of inversion results the [1 1 1 1] contrast is not very
meaningful because the images are always different from zero. So you
can show your average beta image but there is no statistically
meaningful question you can ask about it. However, it would be nice to
get the peak of the F statistic in the right place, which doesn't seem
to happen. I have a similar example from my own data that I'm planning
to look into and I'll let you know if I find the problem or need your
data. Do you get meaningful results from your other contrasts?
Vladimir
2010/4/30 Sun Delin <[log in to unmask]>:
> Dear Vladimir,
>
> I am sorry that I have to send you the email directly because the email size exceeds 500K limit of SPM mailing list. I met a problem when I was doing 2nd level analysis on ERP group inversion data. I am trying to locate the source of the P1 component in a 2*2 factorial designed visual experiment. Averaged data for each condition of each subject were included in the group inversion processing, and the smoothed output images (FWHM = 8mm) were involved in the 2nd level group analysis of full factorial design. The result of group inversion is really encouraging that I could find significant activation at occipital regions during 70-129ms after visual stimuli onset (an example for one condition in an individual subject could be seen in 'sw_sbj214-1_4.nii' attached). The beta images after 2nd level analysis are also beautiful (an example please see 'beta_0004.hdr/img' attached). However, the results of t or F test (please see 'spmF_0001.hdr/img' attached. I would like to see t!
> he P1 component in all conditions, therefore the contrast is [1 1 1 1]) seem greatly different from traditional SPM results. I have tried normalization (proportion scaling or ANCOVA) but found little help. Would you please have a look and give me some advice?
> BTW, is there any difference between fMRI and EEG in the 2nd level analysis? It seems that estimation of fMRI could provide some main and interaction results automatically.
>
>
> Bests,
> Sun Delin
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