Dear Chiara,
this design seems highly inefficient. From your attachment I guess you
have either condition 1 or condition 2, right? No additional epochs
modeled. As a result, your 1st column in the design matrix correlates
for 100% (negatively) with your 2nd, making one of them completely
redundant (or, dependent). Never model rest conditions, they are
implicitly modeled (through your intercept).
So 1 task regressor per session is sufficient here.
Not sure whether this explains your issue, but it might help.
Best,
Bas
On 01/31/2013 09:32 AM, Chiara Pinardi wrote:
> Dear Sirs,
> we are new to SPM and we have some problems on second level statistical analysis. More in detail we have a block design paradigm with hand sensorial stimuli during two different object manipulation conditions (simple and complex objects) and for the two hands (4 runs ). In our experiment the rest condition has been replaced with a sphere manipulation. Our aim is to evaluate the overall contrasts between object and sphere manipulation (1 -1) , the same contrast for right and left hands separately and finally for the two manipulation condition. We tried to design the first level matrix as composed by 4 sessions (simple/right, simple/left, complex/right, complex/left) and for two conditions (object, sphere). However at the second level it was not possible to replicate contrasts as only one possible value is accepted in the 'define new contrast' menu. Could you please help us? Did we design correctly the first level matrix (which is attached to the message)?
>
>
> Thank you,
> Chiara
--
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Dr. S.F.W. Neggers
Division of Brain Research
Rudolf Magnus Institute for Neuroscience
Utrecht University Medical Center
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