Simultaneous action selection

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Rock-paper-scissors is an example of a game which employs simultaneous action selection. Roshambo-Laos.jpg
Rock–paper–scissors is an example of a game which employs simultaneous action selection.

Simultaneous action selection, or SAS, is a game mechanic that occurs when players of a game take action (such as moving their pieces) at the same time. Examples of games that use this type of movement include rock–paper–scissors and Diplomacy. Typically, a "secret yet binding" method of committing to one's move is necessary, so that as players' moves are revealed and implemented, others do not change their moves in light of the new information. Thus, in Diplomacy, players write down their moves and then reveal them simultaneously. Because no player gets the first move, this potentially arbitrary source of advantage is not present. It is also possible for simultaneous movement games to proceed relatively quickly, because players are acting at the same time, rather than waiting for their turn. Simultaneous action selection is easily implemented in card games such as Apples to Apples in which players simply select cards and throw them face-down into the center.

Game mechanics are methods invoked by agents designed for interaction with the game state, thus providing gameplay. All games use mechanics; however, theories and styles differ as to their ultimate importance to the game. In general, the process and study of game design, or ludology, are efforts to come up with game mechanics that allow for people playing a game to have an engaging, but not necessarily fun, experience.

Rock–paper–scissors hand game for two players

Rock–paper–scissors is a hand game usually played between two people, in which each player simultaneously forms one of three shapes with an outstretched hand. These shapes are "rock", "paper", and "scissors". "Scissors" is identical to the two-fingered V sign except that it is pointed horizontally instead of being held upright in the air. A simultaneous, zero-sum game, it has only two possible outcomes: a draw, or a win for one player and a loss for the other.

<i>Diplomacy</i> (game) strategic board game

Diplomacy is a strategic board game created by Allan B. Calhamer in 1954 and released commercially in 1959. Its main distinctions from most board wargames are its negotiation phases and the absence of dice and other game elements that produce random effects. Set in Europe in the years leading to the Great War, Diplomacy is played by two to seven players, each controlling the armed forces of a major European power. Each player aims to move his or her few starting units and defeat those of others to win possession of a majority of strategic cities and provinces marked as "supply centers" on the map; these supply centers allow players who control them to produce more units. Following each round of player negotiations, each player can issue attack orders and take control of a neighboring province when the number of provinces adjacent to the attacking province that are given orders to support the attacking province exceeds the number of provinces adjacent to the province under attack that are given orders to support the province under attack.


Some games do not lend themselves to simultaneous movement, because one player's move may be prevented by the other player's. For instance, in chess, a move of a bishop takes queen would be incompatible with a simultaneous opposing move of queen takes bishop. By contrast, the simultaneous movement is possible in Junta because each coup phase has a movement stage and a separate combat stage; no units are removed until all have had a chance to move. It has been noted that "a certain amount of reverse psychology and reverse-reverse psychology ensues" as players attempt to calculate the implications of others' potential actions. [1] Junta also has simultaneous action selection in that players secretly choose their locations at the same time. [2] This is important in that, for instance, a player plotting an assassination may choose the bank for his or her own location (hoping to quickly deposit the ill-gotten gains) before finding out whether the location of his or her assassination was on the mark.

Junta (game) Board game

Junta is a board game designed by Merlin Southwell first published in 1978 by Creative Wargames Workshop and published, as of 1985, by West End Games. Players compete as the corrupt power elite families of a fictional parody of a stereotypical banana republic trying to get as much money as possible into their Swiss bank accounts before the foreign aid money runs out. Fighting in the republic's capital during recurrent coup attempts encompasses most of the game's equipment, rules and playtime. This game-within-the-game is however actually tangential to the players' main goal.

Simultaneous action selection is used in many real-world applications such as first-price sealed-bid auctions. The fact that no bidder knows what others are planning to bid may provide an incentive to bid high if there is a strong desire to win the auction, which can result in much higher winning bids than if better information were available. The prisoner's dilemma is another classic example of simultaneous action selection. SAS can also be used to introduce an element of chance, as when rock-paper-scissors is used to decide a matter.

A first-price sealed-bid auction (FPSBA) is a common type of auction. It is also known as blind auction. In this type of auction, all bidders simultaneously submit sealed bids, so that no bidder knows the bid of any other participant. The highest bidder pays the price they submitted.

The prisoner's dilemma is a standard example of a game analyzed in game theory that shows why two completely rational individuals might not cooperate, even if it appears that it is in their best interests to do so. It was originally framed by Merrill Flood and Melvin Dresher while working at RAND in 1950. Albert W. Tucker formalized the game with prison sentence rewards and named it "prisoner's dilemma", presenting it as follows:

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of communicating with the other. The prosecutors lack sufficient evidence to convict the pair on the principal charge, but they have enough to convict both on a lesser charge. Simultaneously, the prosecutors offer each prisoner a bargain. Each prisoner is given the opportunity either to betray the other by testifying that the other committed the crime, or to cooperate with the other by remaining silent. The offer is:

See also

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