Video Game Artificial Intelligence

[Person_Man]

I know that this is counter intuitive, but it seems as if the AI on video games is getting worse over time. A particularly annoyance of mine is that turning the difficult up on any game just gives the enemies more stuff (more resources, more damage, more hit points, etc) instead of making them more intelligent. And so being good at a video game basically boils down to having good timing and practice, rather then making smart decisions or figuring out better strategies.

Does anyone have any examples of games with really good or really bad AI, and what makes it so?

[Makensha]

I first think it is worth noting that a lot of AI is intentionally designed to be bad for various reasons. Like in Dynasty Warrior the AI is bad because the enemies are terrified of you. In the a lot of the Naruto fighting games the AI is bad because if it was not you would just get countered on every move. MMO AI is bad because tanks need to be relevant.

Also it is less resource consuming to have a single AI with modified stats for various difficulties than to actually have smarter AI. This way you can actually make the AI really good to start with and then just make their health/damage get weaker as you progress from Nightmare to Easy Mode.

[Grif]

I know that this is counter intuitive, but it seems as if the AI on video games is getting worse over time. A particularly annoyance of mine is that turning the difficult up on any game just gives the enemies more stuff (more resources, more damage, more hit points, etc) instead of making them more intelligent. And so being good at a video game basically boils down to having good timing and practice, rather then making smart decisions or figuring out better strategies.

Does anyone have any examples of games with really good or really bad AI, and what makes it so?

Galactic Civilization II.

It has been designed by Brad Wardell to be a single-player game on the get go. So, the AI was had to be pretty intelligent to compensate.

[houlio]

AI quality also depends on genre. It's much easier to make a good AI for something that relies on a turn-based system over real time since it gives the computer much more time to figure out good moves for itself during the player's turn.

[Triscuitable]

The Halo franchise has also been less than the health factor, and more on "enemies will seek you out and CRUSH YOU LIKE A BUG". The Call of Duty series seems to have given them LESS health, but you as well, making it less gun-ho, and more tactical. Of course, the jam on my face still tends to irritate me. Can we get a hardcore difficulty where health doesn't regenerate unless you use a medkit to only heal a little bit, and limit how many times you can heal in a level?

[Tengu_temp]

I know that this is counter intuitive, but it seems as if the AI on video games is getting worse over time. A particularly annoyance of mine is that turning the difficult up on any game just gives the enemies more stuff (more resources, more damage, more hit points, etc) instead of making them more intelligent.

It's always been that way, and the example you're giving is almost as old as video gaming itself. For a good example, look at X-Com: a widely acclaimed, challenging title thought by many to offer one of the best strategic experiences of all time. The enemy AI is atrocious, and doesn't get better on higher difficulties - only their stats and numbers do.

[factotum]

I agree with Tengu_temp: people who think AI is getting worse are viewing the past through rose-tinted spectacles, IMHO. Having said that, it wouldn't be a surprise if AI *was* getting worse, because the concentration these days seems to be on fancy graphics and particle effects!

Another example of "cheating AI", by the way: Civilisation 3, which is quite old now. You could see the city screens of your enemies if you had a high enough espionage rating (or an embassy, IIRC), which included their current project and how many shields they had/needed to finish it. It was noticeable that the number of shields they needed changed depending on the difficulty level--on the easiest they'd require 12 shields for every 10 you did, but as things ramped up they would be able to build their stuff cheaper and faster than you!

[Grif]

The Halo franchise has also been less than the health factor, and more on "enemies will seek you out and CRUSH YOU LIKE A BUG". The Call of Duty series seems to have given them LESS health, but you as well, making it less gun-ho, and more tactical. Of course, the jam on my face still tends to irritate me. Can we get a hardcore difficulty where health doesn't regenerate unless you use a medkit to only heal a little bit, and limit how many times you can heal in a level?

There is such an FPS in fact. It's called Vietcong (http://en.wikipedia.org/wiki/Vietcong_(video_game)). A massively underrated FPS. You can only heal with morphine or medpacks that was very hard to find. And each gives a diminishing return.

I also feel the AI in the original FEAR were pretty smart, taking cover and actually trying to flank you. Were it not for your game-breaking Matrix powah, that game would actually be a tough cookie. (I tried several of the fights without using the Slow-Mo thing. It wasn't pretty.)

[GoblinArchmage]

Even worse than enemies with bad AI, though, are escort mission characters with bad AI. There have been a lot of times when, due to them being completely and maddeningly stupid, I wanted to brutally murder NPCs that I was supposed to be protecting.

[Leecros]

I think the biggest issue is that many games these days focus on pretty graphics and good effects. In the end they neglect the AI and the story(although that's a whole different topic) and they come out with something relatively easier than developing an AI for each difficulty. The CAI or Cheating AI, where the AI simply gets more advantages than a more advanced strategy. I used to have a screenshot from Medieval II(before it was deleted) of Spain with a dozen large armies on my borders and only...maybe 5 or 6 provinces supporting it. It was ridiculous and i'm starting to see the trend more and more where all changing the difficulty causes is more advantage towards the AI.


IIRC a less extreme example may be Warcraft III(and harder Warcraft II Difficulties) have the AI extract only 1 gp from gold mines and still get the standard rate, 9 in III and 10 in II.





Even worse than enemies with bad AI, though, are escort mission characters with bad AI. There have been a lot of times when, due to them being completely and maddeningly stupid, I wanted to brutally murder NPCs that I was supposed to be protecting.

That just comes into existence because the programmers are silly and decide not to program in a special AI for escort missions.
One exception i know of this is the original Fable where if the escorted is being attacked they flee away from the enemy and usually the player. Then they die because they run into a pack of enemies.

[Airk]

Something that needs to be taken into account as well, is that overall, games have gotten more and more complicated as time goes on. AI has never been particularly good, because, lets face it, it's not something most game devs focus on, and when they do, they frequently do it wrong. But it's now harder to build an AI that LOOKS like it's not stupid.

I read a good discussion on this topic over at GamaSutra a while ago, but the long and short of it is that, yeah, most game companies don't give the guys who are designing the AI (Incidentally, these guys aren't the "AI Guys" they're just people for whom ONE of their many tasks is to put together an AI) the time and resources to do the job right. The problem is exacerbated by the fact that a lot of the time, the designers don't have a clear plan in mind for what they want the AI to do/how they want the AI to behave.

It's just generally a neglected field, due, I'm sure, in no small part to the fact that you don't get a big 'payout' for investing in AI. It's not sexy, it's hard to sell a game with, and only people who care enough to get good at the game are likely to even be able to tell/care about the difference between a "meh" AI and a good one.

[Qwertystop]

Well, SSBB seems to have an improving AI as you increase the difficulty of CPU characters. Level 9 AI will even learn from you game-to-game.

[Triaxx]

The thing about AI, is that TVTropes is perfectly correct. It's really kind of a Crapshoot. You'll find that some games have precognitively difficult AI, while others have AI's that can't succeed at shooting themselves sometimes, much less the player.

[Duneyrr]

Grif is right, the FEAR AI seemed to be rather good, though a lot of their actions may have been scripted.

As for bad AI, I have two words:
Extreme Paintbrawl (http://en.wikipedia.org/wiki/Extreme_Paintbrawl)

[GungHo]

It's just generally a neglected field, due, I'm sure, in no small part to the fact that you don't get a big 'payout' for investing in AI. It's not sexy, it's hard to sell a game with, and only people who care enough to get good at the game are likely to even be able to tell/care about the difference between a "meh" AI and a good one.
Moreover, game makers can and do intentionally dumb down AI and put in artificial stupidity to create a more "realistic experience" and to compensate for the fact that the computer can cheat and react instantaneously to you within their "field of view" if they wanted it to.

If "catch-up logic" was always on and the computer really performed like a computer... or even just a very alert player, then you'd never see an interception in a Madden game and they'd win every fumble. You'd be sniped instantly in a CoD game. You'd be spotted every time you left your butt, foot, or rifle hang out in Deus Ex. Every time you left a city under-defended in Total War, it would be taken away from you. Akira would open up with the SPoD in Virtua Fighter. Ian would never go full auto into your back with a submachine gun.

Ok, that last one I could do without.

[boomwolf]

Yea...AI is actually intentionally dumbed down in many cases because it is otherwise unbeatable, you can NEVER beat computer calculations if he uses his maximum potential because lets face it, you will get a headshot from enemies so far they look like an ant in shooters, will be facing perfect minco-management in RTS games (along a much faster building speed due to "timeless clicks"), instant unbeatable combos in fighting games etc...

The most simple AI is not "not good enough", its "too good of it's own sake"

So yes, their tactics are often sub-optimal. but COULD you win (or have any fun) against opponents who uses super-calculated flank tactics while perfectly aligning every shot, having every enemy calculate trajectories to hit were you WILL be, and perfectly ducking/dodging every time you shoot?

[Leecros]

Yea...AI is actually intentionally dumbed down in many cases because it is otherwise unbeatable, you can NEVER beat computer calculations if he uses his maximum potential because lets face it, you will get a headshot from enemies so far they look like an ant in shooters, will be facing perfect minco-management in RTS games (along a much faster building speed due to "timeless clicks"), instant unbeatable combos in fighting games etc...

The most simple AI is not "not good enough", its "too good of it's own sake"

So yes, their tactics are often sub-optimal. but COULD you win (or have any fun) against opponents who uses super-calculated flank tactics while perfectly aligning every shot, having every enemy calculate trajectories to hit were you WILL be, and perfectly ducking/dodging every time you shoot?

you DO know that the term AI in video games is misleading right? Everything they do is programmed in. It's not a free thinking Intelligence that would fit the definition of "Artificial Intelligence" . The programmers don't just take an AI, shackle it, and put it into a game. The AI in video games is a Virtual Intelligence, a bunch of code designed to act and react to what you do. In really bad video game AI's you can abuse this fact to predict what it's going to do. Yes, if we were to go up against an AI we probably wouldn't last too long, but the term AI in video games is a Misnomer, because everything it does is pre-programmed, it doesn't actually think freely as an actual 'defined' AI would.


With that said, the old dinosaur game, Descent, i always thought had very excellent AI, especially for it's time. The bots were programmed to do a variety of things. I believe the three major categories(it's been awhile since i've read an article on it) were Guards, Hunters, and Chargers. Or at least that's what i would call them. Guards would guard the doors and shoot at you. You couldn't lure them away, although on lower difficulties they could get knocked out of the way to a point they won't travel back. Hunters stalked the tunnels on an active search and destroy mission. They would wander around and shoot at you on sight and try to get behind you if they could. Then there are Chargers, oh how i hated that type of AI when i tried to play harder difficulties. They would hide behind walls and then fly out and shoot at you just before they would become visible, they would get behind you and fly at you, shooting all the way to give you less of a chance to avoid their shots, they were pretty much the bane of your existence because it was very difficult to not take damage from them if you didn't know they were there and even if you did and with the higher difficulties...your hp was a valuable resource. Of course the game was based on Rogue AI going...well, rogue. They were designed with 100% accuracy in mind, if they shoot at you they will hit you unless you change course which made it very dangerous in tight spaces(which you're in mineshafts...tight spaces were abundant)

[Airk]

You guys are missing the point though - the "unbeatable AI" that you are saying existing AI is "dumbed down" from is in fact, just a different form of BAD AI. When people say AI isn't "good", they don't mean "It doesn't react fast enough" what they mean is "It doesn't do a good job of emulating a person who is about as good as, but slightly worse than me at this game."

That's the real point of AI design - not to react instantly or not, or make decision X or decision Y. This means that you are not building the "best" AI from a decision making standpoint, or a gameplay standpoint, or anything like that.

More specifically, a good AI needs to:

Have limited inputs, in the same sense that a player does. No one likes an AI that reacts to things they shouldn't be able to (like knowing exactly when you will emerge from behind a corner)

Have deliberately reduced reactions. A computer can pull a trigger or execute a dragon punch the instant it computationally realizes it's time. Humans can't. There needs to be a delay.

Have a certain amount of randomness. Humans don't always react the same way, or with the same speed and accuracy, so a good AI shouldn't either. This is also an easy place to put your "difficulty slider", such that an "easy" AI will miss 50% of its shots, whereas an "Insane" AI may only miss 5%.

For more in depth discussion of this sort of thing, you can probably start HERE (http://www.gamasutra.com/view/news/35425/Opinion_The_AI_Is_A_Lie.php) and spend more time on that site in general.

[Sipex]

I have to agree about Halo AI, it does tend to get deliberately 'smarter' as the game goes on.

Halo Reach especially so. I tried to beat Reach on the hardest difficulty (can't remember anymore) and got fed up after a while but then played 3 for some reason (someone needed the achievement) and noted that the AI was significantly smarter in Reach.

[Triscuitable]

There is such an FPS in fact. It's called Vietcong (http://en.wikipedia.org/wiki/Vietcong_(video_game)). A massively underrated FPS. You can only heal with morphine or medpacks that was very hard to find. And each gives a diminishing return.

I also feel the AI in the original FEAR were pretty smart, taking cover and actually trying to flank you. Were it not for your game-breaking Matrix powah, that game would actually be a tough cookie. (I tried several of the fights without using the Slow-Mo thing. It wasn't pretty.)

Yeah, PM's Supernatural powers really did make the game much less of a grind, and more "SLOOOOOOOOOOOOOOOOOW". I feel NOVA 2 on the iOS really took this to heart, because the game is freaking broken when your super-powers are powered by your health, and you can regenerate health, and you can slow down time... During which your health can regenerate.

But Vietcong... I'm gonna buy that. Thank you.

[Triscuitable]

I have to agree about Halo AI, it does tend to get deliberately 'smarter' as the game goes on.

Halo Reach especially so. I tried to beat Reach on the hardest difficulty (can't remember anymore) and got fed up after a while but then played 3 for some reason (someone needed the achievement) and noted that the AI was significantly smarter in Reach.

Funny thing, every level streams to the game on the disc, in lower detail from a distance. AI is far more limited at a distance, to save power, but it means you can back WAY up, and get a clear and easy shot. And by way up, I mean literally, back and WAY up. The impossible direction. The AI actually has more processing speed devoted to it as you get closer, meaning things like noticing you, flanking you, and other things are performed more often. Also, the Covenant has motion trackers.

[GolemsVoice]

The S.T.A.L.K.E.R. series always featured a quite well designed AI, which could perform many actions and would try to flank you or seek cover. I think this was one case where they actually had to dumb down the AI because it was just too good, or rather, it used the advantage of being a computer too well.

It also has an escort mission where you have to escort a group of Stalkers through an anomaly field (think a field full of acidic pools and the like, and the NPCs where quite adapt at not getting gibbed.

[littlebottom]

I know that this is counter intuitive, but it seems as if the AI on video games is getting worse over time. A particularly annoyance of mine is that turning the difficult up on any game just gives the enemies more stuff (more resources, more damage, more hit points, etc) instead of making them more intelligent. And so being good at a video game basically boils down to having good timing and practice, rather then making smart decisions or figuring out better strategies.

Does anyone have any examples of games with really good or really bad AI, and what makes it so?

well i know exactly what you mean, but a game that made me smile when you turned up the difficulty was valkiria chronicals, it added more enemies in strategic positions, being as the game was a turn based strategy, it actually made it more difficult. unfortunately the game itself made you strive for 1 of two things, over all victory, or the fastest victory possible, and the fastest victory possible usually just meant use snipers to take out strategic enimies, then charge your fastest character to the enemy main base and drop a grenade then take the base if possible. often occupying the enemy main base was the objective, although only possible within a few turns most of the time, anyway, what was i talking about again? oh yes, AI. most AI i have faced against recently has made me laugh for one reason or another, i remember when AI actually meant something other than "being fired at, go behind cover, continue firing back" yeah, so maybe that is what a human would proberbly do. but true artificial intelligence would add people who freeze in fear the first time they end up in a gun battle and have crises of concience when they are about to kill someone:smallamused:

[Grif]

You guys are missing the point though - the "unbeatable AI" that you are saying existing AI is "dumbed down" from is in fact, just a different form of BAD AI. When people say AI isn't "good", they don't mean "It doesn't react fast enough" what they mean is "It doesn't do a good job of emulating a person who is about as good as, but slightly worse than me at this game."

That's the real point of AI design - not to react instantly or not, or make decision X or decision Y. This means that you are not building the "best" AI from a decision making standpoint, or a gameplay standpoint, or anything like that.

More specifically, a good AI needs to:

Have limited inputs, in the same sense that a player does. No one likes an AI that reacts to things they shouldn't be able to (like knowing exactly when you will emerge from behind a corner)

Have deliberately reduced reactions. A computer can pull a trigger or execute a dragon punch the instant it computationally realizes it's time. Humans can't. There needs to be a delay.

Have a certain amount of randomness. Humans don't always react the same way, or with the same speed and accuracy, so a good AI shouldn't either. This is also an easy place to put your "difficulty slider", such that an "easy" AI will miss 50% of its shots, whereas an "Insane" AI may only miss 5%.

For more in depth discussion of this sort of thing, you can probably start HERE (http://www.gamasutra.com/view/news/35425/Opinion_The_AI_Is_A_Lie.php) and spend more time on that site in general.

Funny enough, I find the bots that were being created for Half-Life (and their assorted mods) to be more intelligent than some of the more modern games. Have you tried PODBot for Counter-Strike? It featured randomisation (in their pathing and aiming ability), a delayed reaction time, an actual decision making process (follow the player? rescue the hostage? camp? guard an important choke?) and all that jazz. The only thing keeping it back was the fact that it was able to see through shootable objects, but that was more of an engine limitation rather than any fault of the bot.

Another case in point? REALBot. This bot learns your every move. Every single one. Yes, so each time you play crossfire, they try to emulate your exact move. Granted it makes them dumb to the point of easy kills at first, but they get drastically better the more you play the map.

[KillianHawkeye]

There is no way that game programmers are going to make a whole new AI for each difficulty level in the game. It's WAY EASIER to use the same AI and just adjust some other numbers (like resources or enemy stats or whatever) to change the difficulty.

[factotum]

I suspect most game AI is actually what should be called an "expert system"--these are usually collections of rules that need to be followed (e.g. if human player moves to this location, move to here and shoot). You should be able to make such a system "stupider" by simply switching off some of the rules!

[Gwyn chan 'r Gwyll]

STALKER AI is great fun! I love getting into such intense firefights! Hide behind a car, take out a few bandits... so much fun!

[Makensha]

I enjoyed Medal of Honor's Rising Sun AI. If you shot the AI in the foot they hop around. :smallbiggrin:

Ok, maybe not the best example of AI, but it really was a highlight in an otherwise average fps.

[Leecros]

There is no way that game programmers are going to make a whole new AI for each difficulty level in the game. It's WAY EASIER to use the same AI and just adjust some other numbers (like resources or enemy stats or whatever) to change the difficulty.

It's not like they would have to build a whole new AI for each difficulty. It's quite reasonable to advance the AI you already have and improve it for higher difficulties.

[houlio]

It's not like they would have to build a whole new AI for each difficulty. It's quite reasonable to advance the AI you already have and improve it for higher difficulties.

I think this is what Galactic Civilizations II does, where lower difficulty levels disable some of the decision making algorithms in the AI.

Another game with some pretty intense AI is AI War, funnily enough. The AI isn't particularly intelligent, but it makes really weird and often unpredictable decisions, making the enemy really difficult to predict.

[Brother Oni]

One example of an AI that properly gets harder when you crank the difficulty up - the ones for board games like chess, although they're probably not 'thinking' in the way that we understand it, they're probably computing the statistically best move in for that current board position.

However certain games like Go tend to make programming difficult as the number of possible moves pretty much remains consistent throughout the game, unlike chess where it decreases the longer the game goes on.
For example, I have a basic understanding of the rules of Go and I can hammer the computer on the hardest difficulty on a standard 19x19 board, while conversely I have trouble beating the computer on medium on the training 9x9 board.

[Triscuitable]

One example of an AI that properly gets harder when you crank the difficulty up - the ones for board games like chess, although they're probably not 'thinking' in the way that we understand it, they're probably computing the statistically best move in for that current board position.

However certain games like Go tend to make programming difficult as the number of possible moves pretty much remains consistent throughout the game, unlike chess where it decreases the longer the game goes on.
For example, I have a basic understanding of the rules of Go and I can hammer the computer on the hardest difficulty on a standard 19x19 board, while conversely I have trouble beating the computer on medium on the training 9x9 board.

I used to play go. I really do suck at it. So I made up crap for it. Then suddenly it's "Action-Reversi", and stuff apparently blows up. It was awesome. My board lies in my bedroom. I haven't played in years.

I enjoyed Medal of Honor's Rising Sun AI. If you shot the AI in the foot they hop around. :smallbiggrin:

Ok, maybe not the best example of AI, but it really was a highlight in an otherwise average fps.

My god, I wasn't the only person to play that then! I played split-screen just to go around with a weak pistol and fire on every enemy soldier's foot. We made a game out of it. "Break-dancing under the rising sun."

[Triaxx]

Both the Goldeneye, and Perfect Dark AI's from the N64 would hop up and down if shot in the foot.

[factotum]

Both the Goldeneye, and Perfect Dark AI's from the N64 would hop up and down if shot in the foot.

I wouldn't call that an example of "good AI"--there was probably a single rule in there that said "If foot hurt, hop". A good AI would have the wounded soldier duck behind cover and have his friends lay down covering fire while he crawled away!

[Togath]

One example of moderatly good video game ai I've encountered are probably(some of) the mobs in DDO, while I would imagine that the programing for them isn't very complex, they actually do prove a challenge when they go for alarms or try to lure you into traps.
Though I've mainly encountered this with kobolds and undead(intelligent undead, the mindless ones just mill about aimlessly unless they see you).

[deuxhero]

The AI is getting dumber for two reasons.

1: The budget is going to shiny graphics and celebrity VAs
2: Modern game players are turned off by anything resembling difficulty (at least acording to publishers not called Atlus and sometimes Nintendo)

[Brother Oni]

2: Modern game players are turned off by anything resembling difficulty (at least acording to publishers not called Atlus and sometimes Nintendo)

Modern casual gamers, yes. The hardcore gamers are still there plugging away, but they're in the minority as they've always been.

Casual gamers vastly outnumber the hardcore ones, so if a company wants to sell its product to as many people as possible, toning down the difficulty is the first step.
Since it costs more to put a game out these days, maximising sales is pretty much the major concern of any company with investors (small indie companies don't have the same risks of big ones, thus they have more flexibility in making more risky titles).

[GolemsVoice]

The AI is getting dumber for two reasons.

1: The budget is going to shiny graphics and celebrity VAs
2: Modern game players are turned off by anything resembling difficulty (at least acording to publishers not called Atlus and sometimes Nintendo)

I assume you have some manner of proof for this, besides "it's obvious!!!!" and nostalgia goggles?

[deuxhero]

Interviews with the bigs like Bioware, Bethesda, shooter makers, ect all consistently say difficulty is a turn off.

[Grif]

I assume you have some manner of proof for this, besides "it's obvious!!!!" and nostalgia goggles?

To be honest, I don't find AIs to be any dumber or smarter than the games of the previous generations. (with the exception of exclusively single player games like GalCiv II and user-created AI.)

I mean, c'mon, you can hardly call DooM's monster AI to be superior to CoD enemy AI. Even Half-Life, had a fairly basic AI which was for most part, adequate. (I think Opposing Force had better AI than the base game for some reason.)


Interviews with the bigs like Bioware, Bethesda, shooter makers, ect all consistently say difficulty is a turn off.

That's not proof of dumber AI. There are many ways to turn down the difficulty. Most notorious was the concept of regenerating health, which I abhor. Others include simply giving the player more health, just plain make enemies easy to kill or give you bigger guns.

[Dublock]

With that said, the old dinosaur game, Descent, i always thought had very excellent AI, especially for it's time.

I quoted only part of it, but I agree with everything you said and I love that game. I spent a good portion of time playing that one.

But I do agree with the general idea that the overall AI (which as someone mentioned is not a true AI is correct) is a bit lacking at times. I get annoyed at Civ with it "cheating" for the win. I rather set up myself in a disadvantage and play that way on a more even setting then play on the harder settings.

If the AI matches the style of the game, I have no problem in general.

[Gralamin]

So game AI is dumb for a number of reasons, going from time and budget, all the way to Dumbing it down so a player can live.

Most AI is actually scripted: A bunch of behaviours depending on a finite state machine with a default behaviour. Anything unexpected will simply dump the AI into it's default strategy. This is why, for example, there are safe spots in Pacman. Most games use this, and it is not that the AI is getting dumber, it is that the games are becoming more complex, even if you can't tell, and it becomes harder to produce an AI that "seems" at the same level. Obviously the only ways to increase the difficulty of a scripted AI is more "stuff" or switch to a different script.

Some AI is more clever: This is usually done through a machine learning approach, or a X-ply Alpha-beta search. The machine learning approach can be anything from: Being trained on developers games, learning from the players, learning within the map, or a large number of random simulations. X-ply alpha-beta search is used when actions can be easily defined to happen based on some order (Such as a Turn-based strategy game). Very few games use this, which is a shame, since it is relatively easy to adjust the difficulty (Increase the ply for the Alpha-beta search, or provide data to train the different AIs on based on higher level players. Or even provide more or less data.)

A lot of AI cheats: This is because imperfect knowledge AI is harder then perfect knowledge AI. And because sometimes they need a hack to make up for having to fix it.

As usual, the genre of the game does matter. For example, right now Research into creating AI for Starcraft 1 (http://eis.ucsc.edu/StarCraftAICompetition) is almost all scripted, but with some awesome (http://www.youtube.com/watch?v=8EXW6wbW0n0&list=UUWR5BmX1eJVzlCmQMzw8Z_g&feature=plcp) results.


Edit:

One example of an AI that properly gets harder when you crank the difficulty up - the ones for board games like chess, although they're probably not 'thinking' in the way that we understand it, they're probably computing the statistically best move in for that current board position.

However certain games like Go tend to make programming difficult as the number of possible moves pretty much remains consistent throughout the game, unlike chess where it decreases the longer the game goes on.
For example, I have a basic understanding of the rules of Go and I can hammer the computer on the hardest difficulty on a standard 19x19 board, while conversely I have trouble beating the computer on medium on the training 9x9 board.

A good Chess program uses a Search strategy, looking a few moves into the future, and choosing the best one, assuming you will do the worst response for it (Well there is a bit more to it then that, since the amount they look ahead can vary as they check moves). This is why you rarely see Chess AIs do something "risky". Chess has something in the realm of 10^30 game states. (Checkers, a game that has been solved, has about 10^20 for reference)

Go is actually so complex for a computer: On the standard board we are looking at 10^100 states. This is pretty much insane. A lot of promising research is coming out of simulating through entire games and learning from them, however (A Monte Carlo simulation). This is also why the 9x9 board is harder. It's much easier for a good program to deal with a problem exponentially smaller.

[Ailurus]

To be honest, I don't find AIs to be any dumber or smarter than the games of the previous generations. (with the exception of exclusively single player games like GalCiv II and user-created AI.)

I mean, c'mon, you can hardly call DooM's monster AI to be superior to CoD enemy AI. Even Half-Life, had a fairly basic AI which was for most part, adequate. (I think Opposing Force had better AI than the base game for some reason.)


Actually, in my experience, it does seem dumber, at least in RTS games. To stick exclusively with Blizzard, a couple friends and I played 2-3 humans vs. 5-6 AI matches for literally years in Brood War. Frozen Throne, the AI is far from a genius (and has some dumb habits like walking lone workers into a base which is under attack), but shows some intelligence both on macro and micro levels, most notably (IMO) retreating when outgunned if you catch it out creeping.

The starcraft 2 'AI?' Beyond atrocious. There seems to be only three settings on it: "do nothing", "just blindly send attack waves consisting of all my available military units at you (it literally has no concept of defense)", or "cheat to get immortals out before a human player could hope to build a factory, and then just spam attack saves of higher level units)." All the so-called difficulty levels are just different levels of dumb or cheater.

Blizzard made decent AIs in the past. But there's a reason my friends and I stopped even trying to get a decent 2-3 human vs. 5-6 AI game less than a month after SC2 came out.

[deuxhero]

There are many ways to turn down the difficulty

You over estimate publisher intelligence.

[Spartacus]

Blizzard made decent AIs in the past. But there's a reason my friends and I stopped even trying to get a decent 2-3 human vs. 5-6 AI game less than a month after SC2 came out.

Bronze level players have reported having little trouble with Very Hard, and yet even top Grandmaster level players lose to Insane in a straight up macro game. It takes lots of trickery or just plain cheese to beat one.

[GolemsVoice]

You over estimate publisher intelligence.

While you keep spouting nothing but run-of-the-mill, unsupported, and not very helpful "facts"

[Ailurus]

Bronze level players have reported having little trouble with Very Hard, and yet even top Grandmaster level players lose to Insane in a straight up macro game. It takes lots of trickery or just plain cheese to beat one.

True. But is that because of actual intelligence, or because the AI rush is that much faster and more effective because they have very low build/production times and a 30-40% increase in resource gathering?

[Spartacus]

Oh, sorry I forgot to finish my thought. Insane uses the same AI as Very Hard, they just get huge advantages over the player that are insurmountable without exploiting the weak AI.

[Brother Oni]

Go is actually so complex for a computer: On the standard board we are looking at 10^100 states. This is pretty much insane. A lot of promising research is coming out of simulating through entire games and learning from them, however (A Monte Carlo simulation). This is also why the 9x9 board is harder. It's much easier for a good program to deal with a problem exponentially smaller.

Well that plus the komi handicap is worth a lot more on a 9x9 board. 4.5 points isn't so difficult to overcome on a board with 361 positions, but a lot more with only 81.

[Leecros]

I remember one time me and my roommate were playing Sins of a Solar Empire on Very hard(or was it hard...i don't remember). It was harder than medium. We played a 2 vs 1 game because we figured we would need that extra advantage(oh boy were we right) . I don't think we were playing the game for half an hour before i had a massive fleet show up and slaughter me. I'm talking hundreds of ships. It was ridiculous.


I've noticed several games that i have played where the differences between the 'normal' difficulty and the next level up are just too massive to the point where you may think that the normal difficulty is too easy, but at the same time the next difficulty up is way too hard. I believe there should be a more gradual change between the difficulties...Yes, a skilled player will eventually be able to beat the AI, but that doesn't stop the difficulty from being agonizing until the player compensates.


Another example of annoying AI difficulty settings was in Empire At War(say what you want about the game, the space battles were Amazing). The enemy AI wouldn't even build their Star Destroyers or Mon Calamari Cruisers until you put the difficulty on Hard. Then you have the problem of MASSIVE fleets of them. I recall one time playing on hard and running into a fleet of 200+ Star Destroyers. That is... a lot