fScan Reference Manual, Chapter 2 (CmdLineOptions): group
usage: -group grouptask maxgrps
This option allows you to specify how to group images together in the analysis. Normally, images are divided into bins for averaging and other statistical tests based on their task codes (see -reference options). The grouping option (-group) allows you to further separate images by subdividing those bins according to a grouping code.
You could also separate bins based on the phase of the cardiac cycle at which each image was collected, as: