The assumption was that gamers would be desensitized and not remember the negative imagery. The result was that there was no difference between the results of the gamers and the non-gamers. Honestly, this test seemed more tailored to determining one's capacity for short-term memory, but I'll take all the supportive studies I can get.
I think it's also worth noting that when I hear people wail and moan about becoming desensitized, it seems more that they're complaining about people no longer being shocked and scandalized, which is not the same thing. Take the Saw films for example, if you'll forgive me going for the low-hanging fruit. A seasoned horror film viewer can watch all of those scenes of gratuitous violence without turning away or feeling squeamish (probably) due to the visual stimulus and still be horrified by the depicted acts and the motivations that drive people to commit them. The viewer is not desensitized, just no longer shocked or scandalized by such depictions.
It bothers me that people feel that this type of research is necessary, particularly when the results are so predictable: games do not desensitize their players, games do not turn people homicidal, games promote socialization, games reduce anxiety and so on. Media and entertainment have managed to go for eons without a single one of them becoming a socially corrosive force to erode our humanity, not even Dungeons and Dragons. I suppose telling the worriers to knock it off is a futile effort, but we can take comfort in this: we're right, they're wrong, and the science is there to back it up.