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On 08/02/17 17:05, Vadim Axel wrote: > Thanks a lot, Guillaume. > > With regard to scaling: as far as I checked, it seems that I can just > multiply (e.g., in ImCalc) resultant con image by a factor according to > the amount of the data each subject has. Will it work for any type of > contrasts? You can indeed apply a global scaling (as in the example on the slide) on the contrast weights at the first level or rescale the contrast image with ImCalc using that same scaling (and change the data type option from its default value). What I wanted to say in my previous email was regarding the situation where you have eg 4 conditions and you compute a contrast [1 1 -1 -1] and let's say that for a given subject there are no trials in the second condition. Creating a dummy condition and setting the corresponding contrast weight to 0 as explained below would create a contrast [1 0 -1 -1] whereas you should use [2 0 -1 -1] (and, even better, divide all of these contrasts by 2*nSession). Best regards, Guillaume. > On Wed, Feb 8, 2017 at 6:22 PM, Guillaume Flandin <[log in to unmask] > <mailto:[log in to unmask]>> wrote: > > Dear Vadim, > > What you can do is add a dummy trial for that otherwise empty condition > at the very end of the session (ie onset = number of scans). It will > stop SPM complaining about it and will let you have all of the design > matrices with the same size. You will still have to adjust the contrasts > so that they always have a zero weight for that condition, and you might > also have to rescale some of the contrasts, see eg slide 12 of: > > http://www.fil.ion.ucl.ac.uk/spm/course/slides16-oct/03_Inference.pptx > <http://www.fil.ion.ucl.ac.uk/spm/course/slides16-oct/03_Inference.pptx> > > Best regards, > Guillaume. > > > On 08/02/17 10:47, Vadim Axel wrote: > > Dear experts, > > > > In my experiment the conditions are defined according to behavioral > > ratings of a subject during scanning. So, in some sessions some > > conditions are missing. I tried to define onsets vector for absent > > conditions as empty, but this did not work (during estimation SPM > > pop-ups a window asking to fill the onsets for this condition). > > Obviously, I can omit the missing condition for this specific session, > > so that number of conditions in this session would be less than > maximal. > > But this will require keeping track of which design column corresponds > > to which condition during contrast creation. Is this the only > available > > solution? > > > > Thanks for the help, > > Vadim > > -- > Guillaume Flandin, PhD > Wellcome Trust Centre for Neuroimaging > University College London > 12 Queen Square > London WC1N 3BG > > -- Guillaume Flandin, PhD Wellcome Trust Centre for Neuroimaging University College London 12 Queen Square London WC1N 3BG