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Believable Stupidity In Game AI
Gamasutra is running a feature written by Mick West, co-founder of Neversoft, about creating game AI that is dumb enough to defeat, yet intelligent enough that its "mistakes" are similar to those a real player would make, thus preserving the illusion that the AI is not just throwing the game.
"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 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. ... 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."
Oh, the humanity! Football games drive me nuts when the AI does stupid things no real person would ever do. Why the hell did my fullback just brush by the linebacker that's right in my RB's way?! Why can't I get my linebacker to stay in his lane on running plays?!
I'd love to see the difference in difficulty in Madden being the difference between playing a Jerry Glanville-coached team vs a Tom Landry-coached team. Instead, all increasing the difficulty does is make your opponents more talented but no smarter. Even on the highest difficulty, FBs don't understand their blocking assignments.
Unfortunately, the AI generally only gets a tiny slice of the CPU time. If it were to use as much as the graphics, etc, then sure: the extra processing required to make the AI believably stupid would be easy. The innovations are there, it's just they are too slow or processor intensive to be implemented in most games.
And vice versa.
One thing that is stupid: trying the same things that failed in the past.
This is a component of smart behaviors as well. If you don't know what to do, try something and watch very carefully how it fails. If you are in a desperate situation and you are going to definitely fail through inaction, then try an action which failed in the past and hope you get lucky. Or vice versa, when the action that usually works looks like its going to fail, try doing nothing.
Animals freezing in the face of danger is an example of this. It's not much of a defense, but you might get lucky. Maybe the prey a couple animals down the line will get itchy and draw the predator's attention.
On the other hand, smart behavior can be a component of stupidity. If the red button gets you a treat 80% of the time and the green one gets you a treat 20% of the time, the intelligently stupid thing is to push the red button 100% of the time. The stupidly intelligent thing is to try to work out the pattern of red/green rewards.
If you want realistic model of stupidity, provide the NPCs with a range of decision making strategies, all of which work to some degree, but the better of which take more effort (computation). The NPC can choose between the strategies with a random function weighted towards the better strategies, but as time and "stress" come into play the function can shift towards the easy but less effective strategies.
That's a pretty good model of human performance "choking".
Evolution did not produce human stupidity because it was useless, after all.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
You're joking, but having realistic actions like teabagging a defeated corpse brings a lot more illusion of reality than a lot of the other stuff they do.
As for the article, I saw a lot of 'dumbing down' and 'intelligent mistakes' ... But I saw absolutely nothing about 'personality'. -That- is what makes an AI seem real.
Take the poker example. If you just create 3 levels of players, bad, good, and perfect... There's no personality.
Instead, you make different players: Cardsharp, timid bets, reckless bets, etc. In other words, you model the AIs after real player types.
In other words, you're trying to pass the poker Turing test with this AI.
"If you make people think they're thinking, they'll love you; But if you really make them think, they'll hate you." - DM
F.E.A.R. is the only game to date that I've played and honestly felt like I was playing against human opponents. Honestly, they were as smart as or even smarter than playing against people online.
They did this through heavy use of waypoints and scripted events. If that's what you have to do to make it realistic, then by all means, do it.
A computer that plays on equal terms.
AIs often win in some games not by the virtue of being smarter, but by having an unfair advantage. Examples:
My suggestion: An AI should be coded as a bot, within the constraints given to the player. If the player can only see a part of the battlefield (like in Starcraft) then the AI should have the same limit and need adjust its own viewport to gain awareness of an area. It should also be limited by the fog of war, and lack the ability to see out of the back of its head. To put in another way, a fair Starcraft AI would be one implemented with a camera pointed at the screen, controlling only the keyboard and mouse inputs.
The idea is that I want to be beaten because the AI is indeed smarter, not because it's got a superior access to the battlefield I can never gain.
Chess probably comes closest to the sort of thing I want -- the AI and human are fighting on very equal terms. I don't see the calculating millions of positions a second as a problem, that's simply an implementation detail.
Why is this debasement? Playing against a machine even in unfair settings is still a challenge. The goal isn't to pick only fights you can win but to test yourself and do something new and experience something new.
As for it being "unfair" it wasn't touted as fair it was a computer v grandmaster experiment not a ranking test.
The only shady part in my opinion is the refusal for a rematch. If the man is willing to play on uneven ground and give his time (even if paid) to your stunt then you should have the courtesy to let him challenge/redeem himself.
Sorry, but as you say I must almost completely disagree with your sentiment on scripted events in games. Scripted events are not good example of AI because there is no decision making, which makes them predictable and exploitable. So the only way to scale difficulty in a scripted scenario is to just pump up the AI's accuracy, damage, and health, which are not very interesting. Scripted events work fine for fairly linear narratives and setting up big cinematic set-pieces, but they don't make for interesting gameplay (mind you I did not say they don't make for "fun" gameplay).
The events you describe in AvP are not necessarily examples of scripted scenarios, but sound more like a scripted set of responses to stimuli the player provides (would the AI react differently if you didn't rip off a soldier's head?). The trick for interesting yet realistic decision making is to allow the AI a range of responses that it can make, and then every time you present the same scenario to the computer you may get a different response. So when the AI is actually making decisions, rather than just following a pre-scripted path, this allows the player to make actual decisions in response, rather than just following their own memorized trial-and-error derived path to success.
The key to a good scaling AI doesn't have to be that tricky, it can just be a matter of what range of choices you allow any given AI to make and what sorts of "mistakes" you throw in that pool of choices.
When I face "easy" opponents in an FPS, I want them to use simple tactics (not just be unable to hit the broadside of a barn) like charging forwards blindly, or getting scared easily and retreating or even panicking, and being easily suppressed by heavy fire. When I face more advanced opponents, I want the range of their choices to move up the tactical scale to include flanking maneuvers, suppression fire, use of cover, and tactical retreats. A good mistake for an advanced AI would be to assume you're in the wrong position if you duck out of view and to attack that wrong position vigorously (as opposed to the omniscience a lot of AI's seem to have). They don't have to be any more accurate or need any more bullets to kill than an easy bot, but at least they could present more of a real challenge without artificially increasing their stats. Granted this is harder to do and would require actual programming rather than just increasing a few numbers, but that's the price for good AI in your game.
I agree with this totally. One of the bigger reasons some players fail at a game is that they aren't actually playing the same game as everyone else.
What I mean is illustrated by some post I read once where some jerk, who was also a rather good player, laid it out bare:
Many people don't play the game. They invent their own little rules for what is "fair" or "better" or "morally right". This handicaps them. You win by playing the game and using all of your abilities and all of your assets to do so, no matter how "cheap" or "skill-less" they seem to you.
If the game makes it so that some skill does more damage for less effort, but you prefer to use another skill because it seems "cool" to you, or you liked the animation or whatever, you deserve to lose.
The one thing that this illustrates is that a computer also tends to have clarity of purpose. They are programmed to kill you. That is what they do. They aren't there to smirk or taunt you (unless that's in the script). They will not dance around or try and add finesse to their moves to look cool. They use the most efficient moves or actions to kill you. Or, sometimes, they only get a certain set of moves, but they are scripted to execute them in a certain manner.
So, basically, by giving your NPCs a "personality" where their goals aren't to strictly kill you with Terminator-like focus, but perhaps to simply make you look bad, or use some moves that *they* think are cool, which really aren't all that useful, you can make them a bit more "human".
The problem with most mobs is that you already know their motivation, so knowing what they will do next is actually rather easy to figure out. So, if you "cheat" with their AI, it becomes apparent to players that you either buffed or nerfed them artificially.
If your mobs act in a manner where they are believably foolish, its a lot easier to handicap them and have a player believe that the handicapping is their lack of "skill", rather than you simply giving them less hit points or some absurd lack of resistance to one damage-type.