Hello,
I have computed the average of the sources among my 17 subjects (Average files, options ‘Everything’ and ‘Arithmetic average’), for 2 different conditions. I then want to compute the difference between the 2 conditions. To do so, I enter the grand average file for condition A and the grand average file for condition B and I select run / other / Difference A-B, and no absolute values. If I then open the resulting file, on the cortex or MRIviewer, I get an ‘Invalid Scale’, with the colors of statistical tests (blue-white-red). If I open the grand average files I get a correct scale (pA.m, blue-green-red).
Why does the difference appear with an invalid scale instead of a regular pA.m scale?
Am I making some mistake in the process?
Thank you in advance,
Mariana
Hi Mariana,
I fixed a little problem that was causing this, you can update and try again.
It uses different colormap categories for the source maps (colormap “sources”) and the difference of source values (colormap “stat2”), so that the default colormap for a difference is a “blue-white-red” color set.
I’m not sure what you are are trying to do with this difference, but it most cases, if you are looking for differences in activation levels between two conditions, you would calculate the difference with option “Use absolute values of the sources” SELECTED.
If not, the sign of the difference is very difficult to interpret… (reminder: sources maps have positive and negative values, but most of the time we are not interested in this sign - to see it, display the sources maps and configure the colormap to display positive and negative values).
Cheers,
Francois
Thank you Francois for you reply!
Best,
Mariana