Hi,
We have been having the following issue regarding fMRI 2nd level analysis using SPM12 (we’ve used a variety of different MATLAB versions to make sure this is not the cause of the issue and it is not, nor is it due to the specific computer used):
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We have been attempting to explore a correlation between task performance and BOLD responses across trial types (high>low), after controlling for age and sex.
Based on every tutorial we have seen, the contrast matrix should show the variables in the following order:
Performance | Age | Sex | H>L (mean/beta)
weighting = 1 0 0 0
However, regardless of how many different ways and times we specify this, the contrast manager shows the following:
H>L (mean/beta) | Age | Sex | Performance
(so we weight as 0 0 0 1)
A peer reviewer has suggested that SPM is treating our performance variable as just another covariate (like age and sex) because the mean/beta is presented in the left-most column. I have attached the matrix from our 2nd level (the weighting is on performance, the right-most variable) .
We don’t believe we are running the 2nd level incorrectly – we have an experienced fMRI researcher on our team who is overseeing the analysis and we have followed all the standard tutorials to the letter (e.g., like this one from Andrew Jahn: https://www.youtube.com/watch?v=OL9wHk9PyTc – but Jahn’s mean appears on the right rather than on the left like ours).
Crucially, we have run a 2nd level analysis using different data which was pre-processed and analysed at the 1st level by different researchers and we still get the same result (with mean/beat in the left-most column).
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We are at a loss to explain why this is happening or what this even means. Our key concerns are:
1. Is the reviewer correct that in our matrix performance is being treated just like age and sex (despite the weighting)?
2. Why is this occurring?
3. Is there a way to fix it (if it needs to be fixed)?
Any help would be massively appreciated!
Thank you,
Jay
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