I Want to Believe
Do Xbox dogs dream of electric sheep? How artificial intelligence helps game developers mimic human—and animal—behavior.
So far, it’s been working out beautifully.
Your squad mate’s bantering at you like a banshee. He’s taking cover when he’s supposed to take cover and firing when he’s supposed to fire, just like a real soldier. And then, in the middle of the big scripted throwdown, he just stands there, stiff as a cheap plywood board, sucking up damage while the enemy’s forces light you up like a Christmas tree in a Target display.
Blam. Believability destroyed. One more video game submarined by a glaring AI flaw.
We’ve all been there, tasted the disappointment and hoped for something better. Like FBI agent Fox Mulder, Ghostbuster Dr. Peter Venkman, and the kids who harbored E.T., gamers are ready to believe—in this case, in video game characters to whom we can relate and who act in the ways we expect them to.
After all, believability is a big part of the reason why Master Chief just landed on Entertainment Weekly’s “100 Greatest Characters of the Last 20 Years” list—even though we’ve never seen his face. Believability is what lets us see Uncharted 2’s Nathan Drake as more than just a self-absorbed Indiana Jones knockoff, and why we’re able to forgive Kratos for his nagging case of bloodthirsty.
Art and Artifice
Believability isn’t something that happens accidentally. As those who’ve peeked behind the curtain can attest, it’s actually the careful confluence of a host of factors, both psychological and technical.
“Believable video game characters are wired from the very beginning for adaptability, to be able to react in real time to what’s occurring in the game, to show emotions and behave in a believable way,” says Dr. Magy Seif Al-Nasr, an assistant professor at the School of Interactive Arts and Technology at Simon Fraser University in Vancouver. Seif Al-Nasr, who just wrapped up a residency at Full Sail University, has spent much of her research career investigating the ways things like lighting, music, and mood can bolster a virtual character’s believability.
“A tremendous amount of work is done with the AI in development to make it happen,” she says.
Seif Al-Nasr points to Ezio, the sleek and deadly hero of Assassin’s Creed 2, and the latest iteration of Prince of Persia as recent examples of characters that ooze believability. But you might be a little surprised by the one she cites as among the most believable she’s encountered:
The dog in Fable 2.
“I actually felt a really strong connection to the animal the first time I played the game,” she says. And she’s not alone. Peter Molyneux and the gang at Lionhead Studios have heard countless tales of gamers who were charmed by the ways in which the dog that accompanies your adventurer seems to respond to the player—pawing the dirt, defending you, and chasing tossed balls. It’s a perfect example of believability.
Well, almost, anyway.
“When the dog worked, it worked really well,” says Ubisoft Montreal’s Stéphane Assadourian, the lead AI programmer for Assassin’s Creed and Assassin’s Creed 2. “You wanted to pet and play with this animal. But at the same time, there were technical aspects of the game that didn’t support that connection—for example, the collision detection wasn’t all that it could have been.” He pauses a beat, then chuckles. “I’ve seen my dog fly too many times to really call it believable.”
Assadourian knows a thing or two about how technology can be used to create—and destroy—believable characters. After all, he led the team that gave us a pair of very believable and intriguing 12th-century Italian killers. In his mind, believability may be underpinned by a game’s technical aspects—things like cinematics, gameplay systems, and top-notch animation—but it really begins with even more basic tools like narration and script.
“There have to be emotions that the player can identify,” he says. “Anything you see or sense has to be something that seems natural to you.”
For example, when Ezio runs, climbs buildings, and perches on rooftops, it seems believable to the gamer, because, says Assadourian, both the script and the game’s free-running system have been carefully planned out to support that.
Use Your Illusions
Seif Al-Nasr calls some of the tools developers use in games like Assassin’s Creed 2 “cheats”—but she’s using it as a term of respect, not a slam. “I worked in theater for a long time,” she says. “And I can tell you this—it’s all about creating the illusion. You don’t need AI to have believable characters in Assassin’s Creed. The scripted sequences make sure there’s believability there.”
Having those kinds of tools in a developer’s arsenal —from strong animators, lighting specialists, and voice actors to top-notch motion capture tech—can be critical, particularly given that the economic demands of a game’s ship date often force last-minute corner-cutting. And in the grand scheme, things like preserving a game’s frame rate will often trump spending extra weeks honing a game’s native AI.
One thing is clear—believability matters more in certain types of games than others. Assadourian points to the ubiquitous Mario, Nintendo’s everyman plumber, as an example of a video game character working with an entirely different standard of believability. Because his mission is so simplistic, the stakes aren’t the same as they are in Prince of Persia: The Forgotten Sands.
“With a game like that, it’s more about fun and how it works,” he explains. “As a gamer, you don’t care about the story, because you’re just here to save the princess.”
In the co-op setting—take a game like Lost Planet 2, which several critics dinged for its weak character AI—the equation changes again.
“You’re far more aware of what the characters in that setting are doing,” says Seif Al-Nasr. “Do they know when to help? Do they know when to step aside?”
Depending on whether you’re playing Daikatana or Half-Life 2, the answer to those questions can obviously vary wildly.
AI and game engines will continue to improve and evolve. As they do, Seif Al-Nasr suspects that it may be the folks working on the “serious games” side of game development—the developers who are working on simulations to train nurses, soldiers, and bomb squad experts to handle real-life situations—who may end up being the ones to achieve a more perfect believability, in no small part because they’re charged with coming as close as possible to recreating reality
Assadourian thinks the entertainment side of game development won’t be giving believability short shrift anytime soon. “Believability is a means to make sure we deliver on so many aspects of what we’re trying to do,” he notes.
“We’re writing software, yes, but we’re also here to entertain the gamer,” says Assadourian. “It has to begin with believability.”
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