4-Player is a new, weekly video game column examining gaming culture on campus and online, documenting a previously unrepresented segment of BU’s culture. 4-Player is co-written by Jon Christianson, Ashley Hansberry, Allan Lasser, and Burk Smyth.
Artificial intelligence (AI) has been important to video games from the start. Even Pac-Man back in 1980 used basic AI to give each of the ghosts a different chasing strategy. Many one-player video games wouldn’t be any fun without intelligent characters in the surrounding world. Convincing and unpredictable artificial intelligence makes games engaging and exciting to play again and again.
While no AI design is easy, video games pose a challenge that other applications do not. In statistical applications like modeling biological systems or in robotics applications like path finding robots, AI developers try to come up with a perfect system. Perfection and optimization, however, don’t always make sense for video games. Non-player characters (NPCs) in video games must be made just imperfect enough to be believable. Enemies that are too skilled make the game too difficult to play, while allies that know too much can make players feel bored. The best NPCs appear nearly human by making mistakes, learning and reacting to stimuli.
Imperfect competition is especially important for many first-person shooters. Enemies with perfect aim would seem unfair and too difficult, but enemies preprogrammed on some predictable script would be boring. One of the first games to impress players with realistic behavior was Halo: Combat Evolved, released in 2001. Enemies in the original Halo take cover behind objects in the world and react to more than just being shot at. They throw grenades back at assailants and retreat when their leader is killed. This AI was further improved in Halo 2, which gave AI “simulated vision and sound.” An engineer on the team, Chris Butcher, said that they “take that information about what the AI can see right now and [they] turn that into a memory structure,” effectively making the NPCs “limited like the player by their senses.” Christopher Natsuume of Ubisoft, where Far Cry was developed, explained that the AI isn’t just a feature of a good game, it is “part of the overall design” that helps make a game great. By introducing an AI that goes beyond just competing against a player to instead simulate real human behavior, games like Far Cry make the whole gaming experience more enjoyable.
It is not just first-person shooters that use AI to create a good challenge for players. The success of turn-based strategy games like Civilization can rely even more on good AI. Brian Reynolds, designer of Civilization II and developer of Alpha Centauri, made similar comments to Butcher about the importance of lifelike reactions from the NPCs. To improve the AI from the original Civilization game and make it more realistic, Reynolds said, he played the game and made notes of where the AI made puzzling decisions. He then reverse-engineered why it made the decisions it did and replaced the faulty logic with how he would have reacted in this situation. While the AI is sometimes erratic, so are humans; it is logical enough for enjoyable play while being unpredictable enough for longevity and durability of single-player gaming.
Ally NPCs need to have carefully crafted personalities as well. One of the most frequently favored AI characters is found in Half-Life 2. For parts of Half-Life 2 and most of the following episodes, the player is accompanied by a female companion named Alyx who helps them along the way. Developers designed Alyx specifically to have a personality that would encourage cooperative play. She was engineered not to perform too many repetitive actions and not rely on routines for combat. Instead, Alyx reacts differently depending on the players actions. A cool example of this cooperation happens underground, when clever players can conserve their own resources by shining a flashlight for Alyx to help her shoot in the dark. By giving Alyx a big personality to complement her reactive AI, developers made Alyx an NPC that players actually want to interact with.
Even NPCs with which players don’t always directly interact are key to shaping the world of the game. Radiant AI, developed by Bethesda, is a system which gives NPCs realistic behavior patterns. The technology is featured most prominently in The Elder Scrolls V: Skyrim. NPCs in Skyrim are given general goals, like daily tasks they must accomplish or a person to meet at a specific location, but are given lots of freedom on how to accomplish these goals. Each character isn’t scripted individually, but rather given an intelligent AI which allows it to react differently at different imps. NPCs in the game, for example, can be seen commenting on things the player has accomplished or interacting with other NPCs that cross their paths. Todd Howard, who is in charge of the development of the previous Elder Scrolls game, says that all this AI works towards creating a more “organic feel” than they could achieve without such an involved system.
Video games present a unique challenge for the field of artificial intelligence. Whether to create a just challenging enough enemy or to make characters that help lead players through a story, AI must be carefully tuned to seem skilled, but not unfair. Games like Skyrim, Half-Life and more, however, have risen to the challenge delightfully. By paying careful attention to the big picture and working to build an interactive world, games that use artificial intelligence are proving to be some of the most enjoyable and durable ones around.