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SAN FRANCISCO — In its quest to make Elizabeth seem like a real-life partner to BioShock Infinite star Booker DeWitt, Irrational’s “Liz Squad” turned to an unlikely source — soccer.

Similar to how soccer defenders try to keep themselves between an attacker and the goal, Irrational’s A.I. programmers did their best to keep Elizabeth on the screen between the DeWitt and his destination, explained lead programmer John Abercrombie at a Tuesday session at the 2014 Game Developers Conference. That way, she could interact more naturally with objects in a way that the player would notice.

It was just one of many tricks that the team used to make Elizabeth seem more real, with others including theater techniques including “exaggeration, blocking, and improvisation.” Whether in tossing an item to player during combat or interacting with objects scattered around the sky city of Columbia, the goal was to make her an active participant in the world.

One of Abercrombie’s key examples was a technique his team employed for battles. In an effort to make Elizabeth more relevant in combat, they would have her call out enemies like snipers. But they soon figured out that players wouldn’t always realize where she was pointing. The solution was to employ a spotlight.


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“We found ourselves needing to provide an icon spotlight on the challenge, much like a dramatic entrance would require a spotlight in the theater,” Abercrombie said.

In maintaining the illusion, the Liz Squad also wasn’t above cheating a bit.

“It is important to realize that in professional game development, we’re not trying to present the perfect or ‘real’ A.I. We’re trying to create entertainment,” Abercrombie said, referring to techniques such as quietly teleporting Elizabeth to the player’s side if they happened to get too far ahead — the better to avoid having to deal with obstacles like railings and other impediments.

“The use of simplistic solutions, clever tricks, or hacks should not be discouraged, because players won’t know what we’re doing,” he said. “They will only know what they see on the screen and hear from the speakers.”

Such techniques did not come easily. According to Abercrombie, they developed these slowly over the course of some four and a half years. When he joined the team in 2013, Elizabeth’s A.I. was “not in great shape,” he said. Goal-side pathing, which Abercrombie credits to fellow team member Tim Austin, didn’t come along until the final year of development. In the end, though, Elizabeth’s “performance” received praise from reviewers.

Abercrombie concluded with the main lesson that he had learned from the experience.

“We must all think about theater and other performance techniques to make our A.I. believable and fun,” he said. “Exaggerations, blocking, improvisation, and even spotlights can be useful tools when presenting your A.I.”

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