The AI of Alien: Isolation | AI and Games #15

Key Takeaways

how do we kill it Ash there's got to be a way of killing it how how do we do it you can't you still don't understand what you're dealing with d perfect organism survival clent like conscience the L what to do of morality I can't lie to you about your chances but you my super [Music] one of the biggest AI driven titles of modern times alien isolation brings the terror of the xenomorph to video games while the alien LV 426 and many other key elements of the franchise have previously been explored alien isolation takes a different route a horror game steeped in the aesthetic in style of Ridley Scott's classic 1979 movie in which the player is trapped on the sylvesta Paul space station with a sole intelligent near Invincible alien for this experience to play out as expected the alien itself has to carry a large amount of the experience a demanding feat for any AI in an industry in which non-player characters are either heavily scripted or suffer really short lifespans so how did developers creative assembly pull this off the short answer is through tried and tested AI techniques designed in a manner that breaks from so many traditional game Design Concepts so stay tuned as we dive in and find out what it is that makes this alien tick what the was that thing the team behind alien isolation built the game around a simple premise to survive an encounter with Ridley Scott's original alien such a feat is pretty difficult to balance given that you need a strong story to carry the player through but also to establish pacing such that the tension varies throughout your game play neither of these are easy when you introduce a systemic AI into play a collection of decision-making systems that are reacting to what's happening in the game it needs to know when it can participate in the experience and at what level it should do so in order to do this it required a unique design perspective as explained by Andy Bray in his talk at the 2016 nuclei conference the player can't be scared all the time otherwise they'll just give up the tension had to vary but also maintain an air of unpredictability in the xenomorph itself this led to the developer seeking inspiration naturally from Ridley Scott's alien movie but also looking at Classic horror movies as well as adventure movies such as Jurassic Park the resulting philosophy could be considered as Psychopathic Serendipity in which the alien always finds itself in the right place at the right time even if you're in hiding and the monster can't see you and it doesn't know your ultimate objective it'll still find a way to mess with your plans however the key to pulling this off was to ensure it wasn't scripted coordinated jump scares while fruitful the first time are cheap and don't yield any further reward in subsequent playthroughs instead the player should have a sense of powerlessness but still know that while the alien is smart they are smarter but all of this goes against the grain of a lot of AAA games development a world in which player empowerment is key this means challenging a lot of design tenants that have been held in pretty much every alien game from Alien 3 and alien Trilogy up to even Aliens colonial Marines the biggest departure from previous games undoubtedly is the fact that you cannot kill the alien you can distract it and in time find ways to hurt it and scare it off but you can't kill kill it ever but in another significant departure there's something of a ro reversal the alien will not only kill you frequently but it does so with one hit ultimately this creature must be a constant believable and threatening presence in order for this alien to work creative assembly fell back on reliable and trusted AI techniques Building Systems that ensure the alien serves its purpose but interestingly also ensures it plays according to expectations to achieve this the game requires two distinct behavior management systems a macro Ai and a micro AI the macro AI is something of an AI director which observes the player throughout the game always watching always knowing where you are meanwhile the micro is tied into the alien itself a series of sensors and behaviors that allow it to hunt down and find the player the director's job is to point the alien in the direction of the player periodically to give it a hint as to where it should be looking despite this the alien AI is never allowed to cheat while the director always knows where you are the alien has to figure it out for itself you can fill it you can surprise it and you can escape it but let's break this down in more detail the director AI of alien isolation was responsible for managing what was known as the Menace gauge a metric that allowed the system to understand how much it was pressuring the player this is rather similar to an approach made in Left for Dead in which a stress gauge was used to prioritize enemy attacks however in this case Menace would come not from attacking the player but being in their proximity and thus raten up the tension as such the system would periodically wish to invoke Menace upon the player which such a one Wonder ful phrase and tell the alien to head to a particular location while the alien is near the player the Menace gauge would increase depending on specific factors such as whether the creature is within a short walking distance of the player whether the player has an actual line of sight and whether the alien was close on the motion tracker but also whether it could reach the player quickly this last one is important as the alien could technically be close on the motion tracker but in another room as such the Menace wouldn't increase as much given there's no real threat naturally once this Menace metric has reached too high a level the director backs off and sends the alien elsewhere either into neighboring areas or up into the air vents the general principle being that when the alien is closer the game is scarier but we need to give players a break after a while not only to ensure they stop freaking out but to enable them to achieve some progress within the game this whole process is managed via a job system previously used no of BioShock Infinite for the companion character Elizabeth which dictates particular tasks to complete the locations that the alien should visit and the priority with which it should do so the priority dictates to the alien whether it should finish what it's doing right now immediately move towards doing this action and blend the required animations or just outright interrupt everything and execute it right now the job system allows the alien to operate in two main states of active and passive the active or front stage mode is when it's told to sweep areas of the map or search specific locations after a certain noise or trigger occurred meanwhile the passive or backstage mode occurs once Menace levels Peak for too long and it falls back into the air vents or such as other parts of the station in some instances it will then actually head for air vents up ahead if it thinks you're going to be moving towards that particular location so enough about the director let's have a look at the alien itself the alien's behavior is Reliant upon Behavior trees a tech we've previously highlighted in our video in the AI of Halo the monster has over a 100 nodes hidden within Its Behavior tree system with the top level of around 30 nodes responsible for selecting what type of behavior it was about to execute these top level nodes would then have the alien execute within large subsections of the tree responsible for specific sub behaviors related to specific tasks to add to this certain parts of the behavior tree are on starting the game locked off the system gradually unlocks these behaviors in the tree as certain conditions are met throughout the game this ensures that the longer you play that the alien starts to exhibit new behavioral traits to keep you on edge from the player's perspective you might actually begin to think that it's learning given your behavior is triggering conditions that are unlocking new parts of the behavior tree though as Andy Bray was Keen to point out none of these conditions come from events that lead to the player's death otherwise the AI May develop an unfair Advantage given you might never figure out what it is that it's learned from your Behavior but also that this game is designed for people to die a lot and every time you do this thing would be getting smarter one concession however is that there are triggers in the final build of the game that unlock behaviors at specific points in your campaign if they haven't already that way the creature can keep up pace with the player as they begin to get better at moving around the space station I can see a power Spike when given a specific job to complete from the director the aliens relying upon a fast and efficient pathfinding system teristics help to dictate the values of particular sensors the alien has the alien has a variety of sensors that allow it to identify with varying accuracy player footsteps when walking or running gunshots and even the motion tracker when the player is around 1 and 1/2 M away now the question that burned in my mind when I played it was whether the alien had sensors built into the tail so as to ensure you don't try and step on it the answer is actually no but in a sneaky move by creative assembly the alien has a very very short range sensor that looks directly behind it it literally has eyes in the back of its head I'm told this is with the intention of ensuring that players do not avoid detection by walking around behind it so the last real thing to cover is the alien's movement those who have played alien isolation will know that the alien is prone to pacing around an environment for several minutes this thing isn't moving towards a specific location in an optimal fashion it's searching it's hunting this is achieved by giving the alien particular areas of Interest either those hand tuned by designers are generated dynamically in the environment to go and head for sometimes these are specific locations the designer wants the alien to visit and other times it's responding to the player given they may be made too much noise a perimeter of nearby locations is established and the alien will devise a path to visit them all in a traveling salesman fashion meaning it will visit every point but not with any guarantee it does so in in optimal fashion given they are prioritized based on their visibility by the alien this suboptimal execution results periodically in the alien backtracking on itself a behavior designed on purpose to give the impression it's double-checking or doubting itself these locations are separated into sear locations those that the alien will visit and spot locations where it will stay where it's standing and then turn to look at the area of interest for safety the designers were able to dictate specific areas the alien never looks so it doesn't catch you out in unfair situations considering all this design effort you'd be quick to think that despite at all the game designers would still allow for the alien AI to cheat periodically by either teleporting or being Clairvoyant in its knowledge according to Bray this is categorically untrue throughout the entire 12 to 18 hour campaign the alen only teleports twice to be in very specific locations and it's only done to enable it to appear in particular cutcenes [Music] alien isolation is an achievement an AI driven game that holds your attention for the most part through the experience of interacting with a primary AI driven antagonist a real feat in and of itself the fact that this is then achieved with within the context of a horror game is all the more impressive fortunately this was largely agreed upon by critics who hailed the alien and its AI Behavior as a real driving force behind the game and certainly worth checking out if you haven't done so already I mean seriously if you're watching this channel just play the games I tell you to doctor's orders we' only just cracking the surface of how this system works for those more techsavvy be sure to catch the full talk by Andy Bray over the 2016 nuclei conference my personal thanks to both Andy as well as Derek pan from creative assembly who are kind enough to humor me and answer some questions I had about the [Music] game with that we bring this video to a close I'm Tommy Thompson and this has been AI in games a series that doesn't happen without the help and support of our sponsors listed now in patreon.com thanks for watching and we'll see youall next time