by Wendelin Reich

<aside> <img src="" alt="" width="40px" /> This is the second post in our series on artificial behavior and modern game AI. Find the whole series via our homepage.



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.

Social cognition 101

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.

Our perception of others is expectation-driven

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.