Heads Up!
In some heads-up games, such as chess and pool, the computer has a
huge advantage over the player. Modern chess programs such as Fritz are
vastly stronger than nearly all human players.
In pool and snooker
games, the computer can be programmed to never miss a shot. However,
people want to play against an opponent that is well matched to their
skills, and so there are generally levels of AI in the game that the
player can choose from.
The simplest way to introduce stupidity into AI is to reduce the
amount of computation that it's allowed to perform. Chess AI generally
performs billions of calculations when deciding what move to make.
The
more calculations that are made (and the more time taken), then
(generally) the better the computer will play. If you reduce the amount
of calculations performed, the computer will be a worse player.
The problem with this approach is that it decreases the realism of
the AI player. When you reduce the amount of computation, the AI will
begin to make incredibly stupid mistakes -- mistakes that are so stupid,
no human would ever make them. The artificial nature of the game will
then become apparent, which destroys the illusion of playing against a
real opponent.
Remember what we are trying to accomplish: We want people to have an
enjoyable experience. No matter what the game, we want the players to
feel challenged so that when they win, they feel a sense of
accomplishment. We want them to feel that they were playing against an
opponent who was really trying to beat them.
By reducing the amount of computation, we create an AI opponent that
is trying to win, but has been crippled in a way that leads to
unrealistic gameplay. But does the player actually care about what is
going on under the hood? What if we don't cripple our AI, but instead
let it play at full strength, but have the AI deliberately throw the
game?
Throwing the Game
In sports, "throwing the game" means one side makes a series of
intentional mistakes that look natural, but result in losing the game.
This behavior is rightly vilified by players and fans, as the agreement
is that there be a contest between two equal opponents, or at least,
two opponents who are trying equally hard to win.
But in computer games, it's impossible to have an equal match. It's
humans versus machines. One side has an advantage of being able to
perform a billion calculations per second, and the other has the
massively parallel human brain.
Any parity here is an illusion, and
it's that illusion that we seek to improve and maintain via the
introduction of intelligent mistakes and artificial stupidity.
The computer has to throw the game in order to make it fun. When you
beat the computer, it's an illusion. The computer let you win. We just
want it to let you win in a way that feels good.
AI programmers need to get used to this idea. We are manipulating
the game, creating artificial stupidity, fake stupidity. But we are not
predetermining the outcome of the game.
We don't set our AI with the
intent to lose the game, but rather to give the human player a
reasonable chance of winning. If the human plays poorly, the AI will
still win, but the player will at least feel like she came close to
beating a strong opponent, and thus feel like playing one more game.
Hidden Handicapping
Computer chess expert Steven Lopez (see Resources) describes how in
human versus human chess, it's acceptable for a high-ranking player to
give a much lower ranking player an advantage at the start of the game
by removing some of his pieces from the board before the game begins.
When the game starts, the master player and the novice player are still
playing to the height of their abilities, and yet the game is more
evenly balanced. The master player does not have to play "stupid" in
order to give the novice player a chance.
However, humans playing against a computer do not like to be given
an advantage in this way, and prefer to play the full board against an
AI opponent of approximately their skill level.
The programmers of Fritz hit upon a solution that involved the AI
deliberately setting up situations that the human player could exploit
(with some thought) that would allow the human to gain a positional or
piece advantage. Once the human player gained the advantage, the AI
would resume trying to win.
At no point here is the AI actually dumbed down. If anything, there
is actually quite a bit more computation going on, and certainly more
complexity.
The goal of the AI has shifted from "win the game" to "act
like you are trying to win the game, but allow the human to gain a
one-pawn advantage, and then try to win." The AI needs to be more
intelligent in order to appear less intelligent.
|
Printer-Friendly Version
When we were working on Rumble Racing, the goal was to make the AI opponents feel like people. We had a matrix of possibility for introduced errors, where at each pathing junction the AI had a choice to take a fast line or slow line. This matched up how people drove the tracks, where small errors in braking and taking the corners made the cars seem to go slower because of poor driving, not simply going slower.
Hey Chris - Rumble Racing was (and is, as I still play it today) one of those great games where one really got to see the AI do some things you'd expect a live opponent to pull off, so it was always a blast to race the same tracks multiple times and almost never see the same result.
g.
This gives moments of hesitation and panic which look extremely realistic (at least in something as simple as driving or fleeing). I've tried to think of a good way to cause the AI to flipflop between decisions only when they are in a panic, however that seems to require breaking good decision making skills (requiring a set amount of time before they can change action).
It's nice to see an article on this subject. A good deal of thought has to go into creating lifelike artificial behavior, and I'm glad to see people in the industry upping their game.
AI should have the same interface to game as the player. All positions and values that bot receives should be slightly inaccurate. AI algorithms should be developed separately from gameplay mechanisms.
If player detects that AI is throwing the game, immersion in gameworld suffers, as the player realises that the whole gameworld revolves around him. I believe the way to go is to introduce quirks and imperfections in AI behaviour, but not have it dominate the game by deciding at which point should the player start winning.
eg: I try to rush into the range and view of my opponents from whence they previously had no knowledge of my presence. Current A.I. would allow all notified opponents to 'snap to' my character and begin firing/ducking for cover with their speed and accuracy determined by difficulty. What I want to happen is for the opponents "psychology" to determine their actions, even though they may be 'trained soldiers.' I just initiated a "surprise attack" and expect them to act surprised depending on a combination of how alert the opponent may be and how efficiently I got within range.
It may sound like what I'm asking for is scripted A.I. set-pieces. In one way yes, but this has much larger scope. To me, realistic 'mistake making' A.I. mean an opponent that "feels." Will retreat because he fears, will fight because he's confident. I'm an artist so I don't know how to implement it, but it would be good to see the A.I. literally go "whoops"
Personally, I like gmaes that use the old D&D system of % to hit; etc; as I always feel like it's an even playing field between the player and the computer. Many games do a great job with AI (like Fallout 3 most recently), but I think some FPS and action games where the AI seems to be on a straight path to the protagonist can benefit from some rpg-style stats under the hood.
John Smith: Try explaining to your producer that you need to develop two different physics systems - one for the game to use, and one for the A.I. ;) Seriously though, your example assumes that with the right interfaces, an A.I. "brain" would act similarly to a human brain, which simply isn't true - even if your A.I. was unable to be accurate, it doesn't mean that it would feel like you're playing against anything analogous to a human opponent.
Games are experiences in which you need to create a suspension of belief, and the A.I. is a tool in that - there will never be a fair fight between an A.I. and a human, but with your A.I. making the right mistakes, you can trick your player into thinking that there is. And at the end of the day, that's all that matters! ;)
C&C 3 is case in point for this.
You mention the prospect of setting up a situation that the player can exploit. That's definitely a fine solution to the handicapping problem! My interest is in the preconditions for setting up such a situation.
As you show with the poker examples, there's usually a reason that a player makes an error, or a type of error which is more typical. (Folding to a big raise, against the odds. That one is a very good and clear example! Folding when "unclear" about the odds... I think this means that you can teach the machine which hands are complicated for a human to calculate the odds for.)
Let me give another example to sharpen the angle I'm getting at.
Let's say we were writing a chess program aimed at beginners (defining 'beginner' as not absolute novice, but rated under 1400). We'd want the machine to make beginner-like mistakes. The first step in "dumbing-down" the AI would be to figure out what kind of mistakes beginners make, and under what conditions. We'd be doing pretty well if we programmed the machine to threaten checkmate when it can be beaten by mate in three. We'd be doing even better if we figured out which kinds of mistakes are more obvious for players (and avoid those). So, the machine wouldn't fall for a sufficiently "obvious" mate in three.
In other words, we'd want a function which evaluates the "cleverness" of a move; the machine, imitating a beginner, is less likely to notice clever moves. Then, when we're setting up a scenario for the player to exploit, we have a believable reason for making the "error."
The AI is not playing the game to win.
The AI is a granny playing with a spoilt brat who throws a tantrum when it loses.
Personally I prefer AI with exploitable weak points, but most gamers are of the spoilt brat variety.
UT used to give the bots fewer shards in the Flak Cannon at lower AI levels, and make the rockets slower... pretty crazy.
We talked about this on the games-and-industry podcast Visiting The Village this week (www.visitingthevillage.com).
For example, take the game Monopoly. there would be specific strategies or "Tendencies" that were predetermined by the programmer to have top priority over other decisions regardless of how useful it was.
For instance, Maud will always buy level 4 properties (The green and blue properties) if able, and place houses on them as soon as possible. This would include a bias of being willing to offer VERY large sums of money in order to acquire there properties or giving up any lesser (according to the bias) property. while at the same time its shunning Level one properties entirely; this would include certain reckless actions, such as trading properties that were not level four even if it owned two out of three of a lesser property of the same color.
This sort of AI gave the illusion that this AI personality had a strategy. you would notice how "badly" he wanted boardwalk and you would hold out for a better offer. You got the feeling you were outsmarting him. and if you picked up on the tendencies, you felt much smarter, and rewarded for victory over them.
I think it would be a nice little tweak to shooter games if personalities were used. Players would know that there were very tactful enemies, as well as overyly aggressive (Reckless) ones. In this instance players can have waves of stupid enemies, mixed with a few, "Hard to kill" Bruce willis types. I think a dynamic AI such as this will enrich most shooters.
Schaeffer recommends that you tune your player so that it is risk-seeking. This doesn't necessarily make it inherently weaker, but if it gives its opponent an interesting game they wil be happier even if they lose.