Heather,
Although there is no direct literature for the GroupAna implementation, you may cite the following paper:
Ziad S Saad, Gang Chen, Richard C Reynolds, Patricia P Christidis, Kenneth R Hammett, Patrick S F Bellgowan, Robert W Cox (2007), Functional imaging analysis contest (FIAC) analysis according to AFNI and SUMA. Human Brain Mapping, Volume 27 Issue 5, Pages 417 - 424.
Gang