Artificial Intelligence in The Sims 3

Hello everyone! My name is Richard. I’m the AI lead on Sims 3, and I’ve been busy working on the Sims’ free-will – what they decide to do when you leave them to their own devices.

 

One big thing we have insisted on from the start is that the Sims won’t need you to hold their hand every time they need to use the toilet. They are now able to take care of their basic needs on their own, leaving you to focus on more important things: building relationships, expanding your career opportunities, and exploring the world around you.

 

But perhaps more importantly than solving the base physical needs, our major focus has been getting the Sims to express their individuality. Each Sim has a personality defined from a large array of traits, and these traits have a strong influence on autonomous behavior. A flirty Sim will preen and pose, while an un-flirty Sim will reject all but the most persistent suitor. Some Sims are family-oriented – you will see them playing games with their children and cooing over them; others dislike children, and can be heard complaining about them loudly.  All the Sims will express their personalities on their own, without needing constant input from you.

 

 

Their personalities affect both what they choose to do, and how they respond to your actions. The pick-up line which worked so well on Pauline may not work quite so well on Bessie Clavell, who has no sense of humor whatsoever! As you socialize with them, you get to learn their personality quirks, and should use this to your advantage.

 

Sunset Valley is a town full of individuals. If you spend a bit of time watching the Sims’ autonomous behavior, you start to get a feeling for what they’re like. Madison Watson is sweet, but perhaps a little immature. The Frio brothers may have a nice house, but they have personality issues which make them less than ideal as boyfriend material.

 

 

Having so many Sims in the town, each with his own individual personality, creates a combinatorial explosion. Sometimes, what looks like a coding problem turns out to be an unexpected side-effect of the Sim’s personality. Recently, a tester had invited another Sim over to her house. Now the AI makes sure that the guest’s autonomous behavior is appropriate based on his relationship level with the host – someone you barely know won’t turn up and start cooking food in your house, but a good friend is allowed to do so. But on this occasion, the guest came straight into the house, walked upstairs and went to sleep! After much debugging and soul-searching, the problem turned out not to be a problem with the code, but with the guest’s personality – she was insane, and therefore impervious to the norms of social propriety!

 

As well as the individual Sims, the town itself has its own separate needs. It wants people to come to work in the morning; it wants the public spaces to be neither too empty nor too full. And, longer term, as old Sims die out and new Sims are born, the town wants to keep the right sort of population density, and a reasonable ratio of male to female Sims. My colleague Peter Ingebretson has done an amazing job at keeping the world progressing over long periods of time.  That’s just a sneak peek at the new level of AI that you’ll find in The Sims 3.  We hope you enjoy playing it as much as we enjoyed creating it.

 

-   Richard

 
Richard Evans
Senior AI Engineer

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