Figure 1: (a) Six players in a game of Imaginary Reality Basketball. Player 15 on the Black team has thrown the imaginary ball at the basket and scored. There is no visible ball; players get all information from watching each other act and a small amount of auditory feedback. (b) Under the hood & invisible to the players, the system represents the imaginary ball as a large number of ball particles, each of which represents one plausible ball trajectory. Players are tracked using accelerometers

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... nd an overhead camera. ABSTRACT We present imaginary reality games, i.e., games that mimic the respective real world sport, such as basketball or soccer, except that there is no visible ball. The ball is virtual and players learn about its position only from watching each other act and a small amount of occasional auditory feedback, e.g., when a person is receiving the ball. Imaginary reality games maintain many of the properties of physical sports, such as unencumbered play, physical exertion, and immediate social interaction between players. At the same time, they allow introducing game elements from video games, such as power-ups, non-realistic physics, and player balancing. Most importantly, they create a new game dynamic around the notion of the invisible ball. To allow players to successfully interact with the invisible ball, we have created a physics engine that evaluates all plausible ball trajectories in parallel, allowing the game engine to select the trajectory that leads to the most enjoyable game play while still favoring skillful play.