Usually, when we think of creating artificially intelligent characters in games, we think of making these characters smarter and better at responding to various situations. But at a Game Developers Conference presentation this week, two industry veterans suggested that we should take lessons learned from the study of human psychology to make characters more believably human, which doesn't necessarily mean "more intelligent."

Conveying emotion is seven seconds

Dave Mark of AI consulting firm Intrinsic Algorithm noted that the average character in many games is an enemy that only appears for seven seconds, which makes it hard to convey any meaningful characterization through traditional methods. Early game characters were like early silent movie characters, according to Mark, making exaggerated movements and using short audio "barks" to reveal their emotions. "Now, maybe it's time for us to learn how to be more subtle like the movie actors did."

Designers can use subtle gestures and small eye and head movements to convey character thoughts and emotions that a player will feel "before they even realize they're there," he said. To demonstrate, Mark showed a live demo of an "egg man" character—just a 3D oval with two eyes. Egg man started out dead-eyed and staring straight ahead, "like a lot of the characters we have conversations with in RPGs." But just by tilting the head and eyes with careful timing, this extremely basic character could express recognizable emotions like shame, suspicion, and distress. With minimal psychological cues, humans will infer what is causing them, Schwab explained, often without even being conscious of it.

These kinds of subtle changes can help make a lot of live game situations much more believable. If a character does a quick double-take glance at a pillar before diving for cover, for instance, it reads as much more human and believable than having that same character just randomly dive because some algorithm told him too, Mark said.

Exploiting player biases

Blizzard Senior AI and Gameplay Engineer Brian Schwab continued the presentation, talking about his efforts to create characters that are less rigidly logical and more recognizably human. "I've played against AI agents that are a pile of logical rules, like Spock," Schwab said disapprovingly, adding that he'd rather have a character that makes human decisions rather than perfect ones.

Schwab described how a number of psychological biases work like "exploit bugs for people," giving a developer tools to trick the player into enjoying a game more. For example, the negativity bias suggests that people tend to remember their failures up to 2.5 times more readily than their successes. While this was probably a useful evolutionary tool, it can turn a player against a game where they lose just as often as they win. The positive rewards in a game have to be much more common than the negative failures to overcome this bias, he said.

Player biases can also wreck the way a game is played, if the developer isn't careful. Thanks to the status quo bias, Schwab said, players will often ignore the wide array of powers and abilities available in a game once they've found one or two strategies that have been reliably effective. Designers can break through this bias only by designing enemies that can't be easily exploited with a single strategy.

Knowledge of psychology can also be used to craft more realistic character behavior, Schwab said. He gave the classic example of a stealth game where a guard checks out a sound caused by a thrown rock for a few seconds before heading back to his assigned post. Realistically, "that guard has absolutely zero motivation to give up on seeing what that sound was," Schwab said. "That's not human at all." Game designers can write around these kinds of problems by creating an important reason for the guard to be called away, for instance, rather than simply having them act like an automaton.