<aside> <img src="https://s3-us-west-2.amazonaws.com/secure.notion-static.com/878728d7-4e6b-41de-93b0-b5670e841989/info.png" alt="https://s3-us-west-2.amazonaws.com/secure.notion-static.com/878728d7-4e6b-41de-93b0-b5670e841989/info.png" width="40px" /> This is the second post in our series on artificial behavior and modern game AI. Find the whole series via our homepage.
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Between the early 1920s and the mid 30s, Walt Disney Studios turned animated characters from a cheap distraction into an internationally recognized art form. Looking at Felix the cat today is a somewhat painful experience, whereas Snow White seems artistically perfect even in the age of CGI. No amount of motion capture or hair simulation could make me feel more of her carefree happiness as she dances with the dwarves.
Felix the cat in Feline Follies (1919).
Snow White and The Seven Dwarfs (1937).
Much ink has been spilled on animation's rapid early evolution and the artistic as well as organizational forces that made it possible. What I want to investigate in this post is the simple observation that video games have not, by any standard, had their Disney moment yet. When animated characters become interactive characters (or non-player characters, NPCs), the illusion tends to break quickly.
Three NPCs in identical 'idle-loops' in Animal Crossing: New Horizons (2020).
Unresponsive NPC in Cyberpunk 2077 (2020).
Trying to feed an NPC in Pokémon Go AR (2019).
I have yet to come across a AAA game with NPCs whose behaviors aren't mechanistic, repetitive, and clumsy. In fact, believable NPCs are so rare across all games that I've had to search long and hard to find examples for this post.
Walt Disney knew that the key to making the audience suspend disbelief and accept animated characters as real, living beings isn't visual realism. Instead, it's about creating believable behaviors. In order to apply his insights to NPCs, we need to understand what makes behavior believable in the first place. I was a researcher in social psychology and artificial behavior before I became a co-founder of Virtual Beings, and I would like to share some research-based insights with you that help shed light on the concept of believability.
The first thing to note is that it's players, not developers, **who get to decide if a given NPC is believable or not. The mental processes that happen when we humans perceive other creatures (human or not) are studied in the field of social cognition. There are three well-established findings from this field that help clarify believability.
Nature (via our genes) and nurture (via our upbringing) have worked together to endow us with assumptions about how the world works. These assumptions start with something as simple as object continuity: If I see you diving behind the couch during hide-and-seek, I take for granted you haven't just vaporized. Infants as young as 5 months are able to achieve this feat.
More complex assumptions concern what happens in other people's heads. Whenever we're with another being, we thus can't help but form expections abouth what this being feels, believes, desires, and so on. Many studies have shown how and why these expectations are useful in 'normal' situations, but also that they are not infallible.
Tom Hanks giving a perfect illustration of the uncanny valley in Polar Express (2005).
When they fail, two things happen: First, cognition becomes slower and more effortful (because it needs to find out which expectations were violated, and why). Second, positive mental states such as visual pleasure, flow or immersion get interrupted and replaced by neutral or even negative ones such as confusion or disgust.
This has been researched for the problem of visual realism and is now known by everyone under the name 'uncanny valley'. What is less known is that it doesn't just apply to imagery but also to motions and behaviors, as illustrated by various GIFs throughout this post.
One of the most robust findings from cognitive science over the last two decades is that most cognition and virtually all perception is automatic. Summarized as 'System 1' in Daniel Kahneman's Thinking, Fast and Slow, automatic cognition is fast, involuntary, expectation-driven and emotional.
The automatic nature of social cognition can be illustrated through a classic experiment by Fritz Heider and Marianne Simmel, first published in 1944. The researchers presented an extended version of the clip shown here to ordinary people and had them describe 'what they see'.
Virtually all subjects spontaneously described the three moving shapes as agents and constructed a story around the events, typically one about the large triangle 'bullying' the smaller one, the circle 'feeling scared', and so on. Try for yourself to see meaningless movements instead of meaningful social actions when looking at the clip - it's almost impossible.
