The above referenced link is a small study that shows the long term effects of violent video games on those that are seemingly unaware of the actually effects the game is having on them. The study was performed with 70 french university students. The students were told that the study was to measure the effect of brightness of video games on visual perceptions. They were then assigned to play a violent or nonviolent video game for 20 minutes on each of three consecutive days.
Really interesting article, and something to consider.