Video games also consumed something else, human attention, in a way that was both old and new at the same time. As in any real game—be it tennis, pinball, or blackjack—the fast-flowing stimuli constantly engage the visual cortex, which reacts automatically to movement. No intentional focus is required, which explains why children and adults with Attention Deficit Disorder find the action of video games as engrossing as anyone else. Unlike games in reality, however, video games are not constrained by the laws of physics, making possible a more incremental calibration of the challenges involved, duration, and related factors in the attempt to keep players coming back.

Tim Wu, The Attention Merchants, loc. 682