Hi everyone. I’m trying to do a conjunction analysis and I have some question about viewing the results.

First, I ran a conjunction analysis,

3dcalc -a zeffortSVcho_age+tlrc'[1]' -b zprobSVcho_age+tlrc'[1]' -expr 'step(a-3.28)+2*step(b-3.28)' -prefix conj_SVcho_ep

and then I opened the conjunction map in the afni viewer. This is my understanding of how to view the results: the voxels where both tasks are above the threshold of 3.28 should have a value of 3 in this conjunction map. So, to view only these voxels I should set the slider somewhere between 2 and 3.

However, when I set the threshold to 2.2, I noticed that the voxels with a value of 2 are still displayed. When I moved the threshold to 2.8, the voxels with a value of 2 disappear. More exploration showed that the voxels labeled 2 were disappearing above 2.5. The problem also extends to the cluster table. If I view the table of results, the cluster algorithm includes voxels with a value of 2 even when the threshold is set to something between 2.01 and 2.49.

I was concerned this was specific to the machine I was working on (AFNI version 16.3.14, compiled on Dec. 7, 2016), so I moved to a different machine. On that machine (AFNI version 16.3.09, compiled on Nov. 16, 2016), the voxels with a 2 were no longer displayed between 2.01 and 2.49 in the viewer, but the problem in the cluster table remains.

Any idea why there are these inconsistencies in viewing are occurring? What should I do to see the true results of the conjunction analysis?

Thanks,
Kendra