Alien Isolation AI: How does the Xenomorph work?

Alien Isolation AI: How does the Xenomorph work?
Matija Huremovic

By: Matija Huremovic

April 19, 2020

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Almost 6 years after its release Alien: Isolation remains a horror masterpiece. Most of the credit to that goes to the titular Alien, or Xenomorph if you prefer.  It features a brilliant AI that serves not only to bring terror and make your heart beat faster, but also to make the Xenomorph seem like a real, and very dangerous, predator. But how does the Xenomorph work in Alien: Isolation? Well, that's what we're here to talk about, so let's explore the Alien AI of Alien: Isolation!

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READ MORE: Is Aliens: Dark Descent on PC a Worthy Genre Experiment?

Alien Isolation AI: The Role Of The Xenomorph

How does the Xenomorph work Alien Isolation

The Xenomorph in Alien: Isolation has one simple purpose – to terrify you. Even though its purpose is relatively simple, the execution of it is anything but. After all, a good horror game doesn't rely on jumpscares. Don't get me wrong, Alien: Isolation has some, but it certainly doesn't rely on them. If anything, they're there to give you a much-needed break from heart-pounding horror the Xenomorph creates.

The purpose of the Alien is to keep you on your toes and keep you constantly planning your escape route. Or several, as the Alien is a highly unpredictable creature. And that's the key to making it as scary as it is. In the game the player can come across the Alien at any point. That means you're never safe, not even when it might appear to be so. Anything you do as a player has a potential to bring the Alien down on you. That includes exploring a room, moving through different pathways, and even just standing still. You are never safe. You are the prey.

Of course, the Alien is just one of the parts in a grand scheme of how Alien: Isolation scares you. Don't get me wrong, it's by far the most important and complicated one, but it doesn't work alone. The imposing fear of the Alien works with other game design elements such as lightning, level design, and sound design to bring out the most of it. Think about it like this: is the Alien scarier when you see it or when you can only hear it moving in a ventilation shaft above you while the lights flicker on and off in the room?

How does the Xenomorph work behind the scenes

Alien Isolation Xenomorph

The first thing you have to know about how does the Xenomorph work in Alien: Isolation is that it has two brains. And no, that thing in its mouth doesn't have a separate brain. The brains in question are actually two different AI scripts.

First we have the so-called Director AI, or the „macro“ AI. Then there is the Alien AI, or the „micro“ AI. These two scripts (it's actually multiple scripts working together as one, but I'll call it a singular script for the sake of simplicity) work in unison to create the terrifying Xenomorph you see before you.

The Director AI in Alien: Isolation

Alien Isolation AI director

The Director is actually a type of AI first used in Left 4 Dead. There it was used to measure and calculate in how much danger any one player is at a given time. Depending on the danger level it would adjust the zombie attacks accordingly. Alien: Isolation took a similar approach in making the Director AI. Instead of measuring the amount of immediate danger the player is in, it measures the pressure it puts them under. More accurately, it measures the amount of stress the player is experiencing.

The way the Director works is by measuring three key elements at all time. The first of which is if the Xenomorph is in the player's line of sight. Then it calculates if the Xenomorph is in a short distance of the player and can it get to them easily. Both of which majorly increase the stress level. Finally, it checks if the Xenomorph is close on the motion tracker but can still reach the player in a short time. Naturally, when it determines the stress level is too low, it increases it by telling the Xenomorph to move to a specific location.

However, once the stress level rises above the certain level for a predetermined length of time, the Directors tells the Xenomorph to back off a bit by sending it to another place. The reasoning behind that is quite simple. As anyone who knows how horror games work, a good horror game will have its ups and downs. Meaning that every once in a while the player requires some breathing room. It can be to make the future scare more effective or simply to allow them to make some progress.

How the Alien AI works in Alien: Isolation

How does the Xenomorph work

How the Alien AI works in Alien: Isolation is a very complicated matter which took hundreds of hours to develop. Meaning that I won't be able to give you an in-depth look at it in this brief article. Regardless, I will explain the general principles behind it and what it uses. But one thing is for sure, the Alien AI is extremely impressive in both its concept and execution. In order to better explain it, I will break down the how does the Xenomorph work in three parts.

Xenomorph behavior that creates terror

Alien Isolation Alien AI

When discussing how Xenomorph works in Alien: Isolation the primary thing you have to know is that relies on something called behaviour trees. Basically, the Xenomorph has several predetermined options on what to do. Each one of those is then split into many more actions which are chosen depending on where it is, what it was doing, and the information the Director gives it. In total, the Xenomorph of Alien: Isolation has about 100 different actions it can execute at any time. Those include things like chasing the player, searching the room, or running away from fire.

But here is what makes Alien AI so great. At the start of the game most of those actions are locked, meaning the Xenomorph won't perform them. What that does is create the illusion that the Xenomorph is learning as you progress through the game. As you, the player, learn new ways of avoiding danger, so does the Xenomorph learn new ways to create it. That's an amazing way to keep you on your toes the whole time. Furthermore, it ensure that you can't use the same strategy over and over for the duration of the game.

So how do more of those actions get unlocked? Simple, their unlocking is based on what you do as a player. Each action in the behavioural tree has an unlock condition that triggers once the player does something. That way the Xenomorph can keep up with you as you progress through the game.

How does the Xenomorph work - the senses

Alien Isolation Pathfinding

Much like real predators, the Xenomorph relies heavily on its two most prominent senses – sight and hearing. That means that when you walk, shoot, knock something over, or even pull out the motion tracker, the Xenomorph can hear you if you're close enough. Of course, all of those things have different range which will catch its attention. Naturally, the gunfire being the loudest and able to summon the Xenomorph from next room. And on the other end we have the motion tracker which requires you to be within 1.5 meters (or about 5 feet in freedom units) from the Xenomorph in order to be heard.

However, the sight is a very fickle thing when it comes to the Xenomorph. Unlike you, it can see quite well in the dark. Meaning that hiding in a soft shadow a few steps away might not always work. But it has another trick up its sleeve. Or whatever the equivalent of Xenomorph sleeves would be. It has eyes on the back of its head. Not literally though, but it can see you if you try and walk too close behind it. This ensures you can't simply abuse the game mechanics and walk right behind it.

The erratic movement of the Xenomorph

Alien Isolation AI Xenomorph Fire

Finally, the last thing which clarifies how the Alien works in Alien: Isolation is the way it moves. Unlike most AI units in games, it does not always move from point A to point B in the shortest way possible. What it does instead is searching, almost without method, and hunting for the player.

If you've ever noticed the way the Xenomorph sometimes roams around the same room for a few minutes in seemingly random patterns you'll know what I'm talking about. What happens under the hood is actually quite simple. The Designer gives the Alien a particular area to explore. That can be done either randomly or in response to a player action, such as making noise. Those nearby locations are then fed into the Alien AI and it chooses a path to visit them all in a non-optimal order. Instead, it prioritises them in order of their visibility to the Alien. Meaning, that if a certain point is most visible to the Alien and it's the furthest away, it will still be visited first.

How does the Xenomorph work so well in Alien: Isolation

Xenomorph AI Alien Isolation

So how does the Alien in Alien: Isolation work so well with everything mentioned? As said before, it is the combination of many things that make the game great, but it is greatly carried by the behaviour of the Xenomorph. One other thing that should be mentioned and has a great influence on creating the terror are the weapons. Or more accurately, the lack of them. Unlike many other games focused on heavy shooting action, Alien: Isolation instead makes you feel much more like Ripley did in the original movie. And that is scared and defenseless. Of course, you get the flamethrower at one point, but the ammo for it is extremely rare and the weapon is hard to obtain. Not to mention that the Alien AI knows how to play around it.

So that's the brief look at how the Xenomorph works in Alien: Isolation and why it's such a great experience. I wholeheartedly recommend you try the game if you still haven't. You can get it right HERE at 2game for a discounted price. So be careful, and I'll see you next time!

Get Your Copy of Alien Isolation at 2GAme Today! 

CHECK OUT: Blink and You'll Miss It: Scariest Moments in Horror Games

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