Breaking the Cookie-Cutter: Modeling Individual Personality, Mood, and Emotion in Characters

Richard Evans, Dave Mark and Phil Carlisle in that order do 20 minutes each on how better to do modeling of personalities for large amounts of NPC’s. An interesting look at normalising personalities, how to do traits, and emotional reaction systems.


Richard Evans (Sims 3)

Richard Evans

Unique personalities in The Sims 3. Want to build a town of unique individuals, where the personalities are obvious. Traits to alter the behavour of the Sims – there are 80 traits, and 5 per Sim. Eg: Unlucky Sims are more likely to get electrocuted when installing a TV, pyromaniacs can set things on fire, etc.

Can now also not necessarily work – can have kleptomaniacs steal things, artists sell paintings. These traits also affect the way they walk, wait (laziness), look (attractiveness) and respond (vegetarians and meat).

The traits are related. You want to maximise the arrows since this is good design, interconnectedness. But you want to minimise it because of the code. Don’t want lots of arrows built as “If Sim is bookworm and object is book” – tons of dependencies. Instead you want to have a data driven systems to link the actions and data with no code.


Add onto this motives – a mean spirited Sim has an extra motive to encourage him to mock people. These motives mean there are 8 different ones per Sim. This also changes over time since the motives are added and removed at run time.

Social cues change the motives at run time – such as visiting a friends house. Can’t really cook food or sleep in their bed unless they really know them well. Insane Sims might suddenly come in and sleep on the bed, or if an inappropriate individual sees something they can disrupt they might well do so.

The social situations are mutually supporting the motives. Read more Arthur Schopenhaur!


With some more fine grained motives, it needs a lot more fine grained interactions – depending on the situtation. Sims 1 and 2 had broad (“Talk”, “Joke”) Sims 3 has more fine grain (“Insult the vegetarian”, “Boast”, “Complement on house”). The personality traits are given in feedback to actions – if you are trying to be funny, if you get positive feedback you find out the target has a good sense of humour.

You get emergent drama from conflicting traits in different Sims, especially in the same house.

Dave Mark

Dave Mark

Different reactions in humans to things like bringing dogs into the room – nice dog, mostly good reactions, mean dog, mostly bad reactions. The variation is lost in games though where the reactions generally are all the responses to nice doggy is pet, all the responses to bad doggy is to run.

Reactions are based on the individual – personality, history, mood and emotion. Reactions will generally be the same if you take the dog away then bring him back. The random factor used in games is out of whack when characters are more persistent.

In a tycoon Sim, the passengers just can be taken anywhere, anyhow, anytime. No individuality, and smaller markets can just be ignored. When we choose travel methods we have preferences on how to travel and when. We have price, duration, arrival time, business class, first class and so forth. There are variations between the people choosing flights.

There are plenty of variations between business, visiting friends and relatives, leisure, and institutional travellers – when they travel, when they book, the destination and distance and so forth.

For a simulator you can rate the preferences of the flight (such as cost) from 0…3 – it is 4096 combinations, more individual models. When you combine the preferences (using preference x satisfaction), you can get widely different scores for each flight.

Phil Carlisle

Phil Carlisle

The mind and the body are one organ really since they affect each other. Dimasio investigated people who didn’t have long term memories – which made it hard for these people to make good emotional decisions.

We have appraisal, which can give you a feeling rather fast – auto-appraisal. It uses memory, which is affected by mood, and relationships – the memory of these.


Darwin looked at emotions in his family, and suggests they are partially evolved. Evolved to do “fight or flight” is evolved from need to avoid dangerous predators? Darwin checked this with an experiment with a snake – glass between him and it but he still jumped back. You don’t have time to think about the reaction even if you don’t want to do it.

The expression can be done wrongly – blank staring faces. There are 7 universally recognised faces which do work though. Doing it with icons – can still tell there are emotions with 🙂 and 🙁

Body expressions are also important. Implementation can be done with appraisals, blackboard and behaviour trees.


Q – How does the modelling work in the Sims 3? – Richard – Got a data driven model and procedural model for the more complex ones.

Q – What else is stopping AI from being more then cookie cutter? – Dave – Time is a major one. Phil – Indie area will have some improvements, and if it is convincing enough people will copy it.

Q – Is the planning in The Sims 3 long or short term planning? – Richard – There are small sequences but it was only prototyped long term plans. Doing it all at run time.

Q – Will players be overwhelmed by the amount of choices for the player? – Richard – I’ve not had much of a chance to play The Sims 3 because I’ve been spending so much time debugging. It is however much more like a mini-soap opera. It is however optional. Phil – we have had a lifetime of training in this too. Dave – A lot of the complexity is there but you don’t have to look at it, can insulate the player with optional information.

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