When using 3dBrickStat, if you use the option -positive, 3dBrickStat -positive (dataset), is that giving you the total number of positive voxels in that dataset but not necessarily their value (i.e. magnitude)? And if I did want to include their value but only the positive correlations would I use -positive -mean (or sum)?
Flags like -positive, -negative, -non-positive, etc., are essentially used to mask the input data, specifying to include the given value ranges. So yes, use ‘-positive -count’ to count positive voxels, or ‘-positive -mean’ to take their mean.
Would using just -positive on it’s own then default to the -positive max value (since -max is default)?
Yes, that is right, assuming not all voxels are negative, for instance.