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Hello,

Thanks for the response on conjunction.  How do you weight the images to find an overlap?  Also, how do you recommend choosing a threshold for each map?  I have read conflicting reports regarding the proper way to threshold in conjunction analyses (i.e. take the square root of the target threshold for two images, but this quickly escalates when, for instance, examining a conjunction of four images). 

Thanks again!

Stephanie

On Thu, Sep 25, 2014 at 5:12 PM, MCLAREN, Donald <[log in to unmask]> wrote:
My approach is to threshold each map, then convert them to 1s and 0s, then use imcalc to form the sum of all of them. If I only have a few images to form a conjunction, I sometimes weight each image to see which images overlap in different locations.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Thu, Sep 25, 2014 at 10:02 AM, Steph Sutliff <[log in to unmask]> wrote:
Hello,

I have a question regarding conjunction analysis in spm8.  I would like to do a conjunction null test using the minimum t statistic to test the conjunction of a contrasts between two groups.  This requires a total of 2 spm.mat files, as each group is modeled separately.  If possible, I would also  like to continue this conjunction analysis by examining two contrasts in two groups, resulting in a total of 4 spm.mat files.

I do not want to test fixed effects, but simply perform a conjunction of two group results, so am I correct in assuming that I should not do a conjunction of all subjects together?  Also, how do I implement a conjunction in spm8 with more than one spm.mat file?  It seems that I can choose only contrasts from a specific spm.mat file.

I really appreciate your help with this!  Thanks so much.




--

Stephanie Sutliff, MSc
Faculté de Médecine, Université Laval
Centre de recherche de l'Institut universitaire en santé mentale de Québec
2601, de la Canardière (F-4500)
Québec (QC), Canada, G1J 2G3
Tel: +1 581-985-2976