Well, the research trio concludes that competition is the keyword, with two subareas: social competition (competing against an opponent controlled by the computer or another player) and competitive situations of the game such as quests, tasks. The explanation for why we choose to play computer and video games for hours on end is the human desire to maintain or enhance the own self-esteem and a positive mood and to challenge and surpass other opponents. These factors are in my view also highly applicable to interactive quiz shows where the viewer may answer the same questions as the teams/person in the studio. The opponents in this case is him/herself, the person(s) competing in the studio and everyone else in the nation sending in their answers.
As for the competitive situations of a game, they are the most important determinant of the enjoyment arising from playing computer games, according to the trio. Simply exploring the options to act in a game may be entertaining as well but doesn't quite cut it. Defeating, say a high level humanoid trogg in WoW, leads to a positive affect on the player. This high arousal state leads to an euphoric experience of enjoyment by which the motivation to continue playing rises. And on the contrary, if you don't manage to defeat the beast, negative emotions are likely to arise, as is an even stronger motivation to continue playing and solve the quest. Although in this case, "the entertainment experience is diminished" Vorderer et al state.
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Evidently, interactivity attract others as well. In their study, Vorderer et al verbally described a given game situation to 349 German gamers. The options were numerous weapons and tools versus little weapons and tools to act with and high/low necessity to act. Turns out that the players expected the first game situation to be more enjoyable, i.e. where there were more possibilities to act. Also, the audience rated the version with few and no possibilities to act as boring.
As for the social competition, not all players strive to compete with other players. Some are very cooperative in their playing. This article written by Phil Agre explains quite well the social interactivity and community practice in WoW. Oh, and if you’re not into reading academic papers, at least check out figure 2 “Top ten happenings that tell you you’ve played wow too much”. I’m guilty of the third one… :)