1. E MOTION I N G AMES Steve Foster

2. E MOTIONS W ITHIN H UMAN E VOLUTION As a product of evolution, emotions have a particular purpose: They have helped humans become the most successful species on earth Emotions bypass the need for deliberative thought by providing biases toward the behaviours with better chances of survival Other kinds of mammals also exhibit emotional capabilities with very similar reactions to humans

3. E MOTIONS I N HUMANS Psycho evolutionary scientist Robert Plutchik believes that there are eight primary emotions, associated in complementary pairs Anticipation and surprise Joy and sorrow Acceptance and disgust Fear and anger His theory states that it's not possible for humans to experience two complementary emotions at the same time; they balance out to provide diversity in the behaviours

4. E MOTIONS I N H UMANS In psycho evolutionary terms, each emotion serves its purpose by triggering a reactive behaviour that's appropriate for survival For example: Fear stimulates the body to release hormones, awaiting flight (or fight) for survival Surprise awakens the senses and forces the brain to pay more attention to perceptions Disgust leads humans to reject the object in question Anger causes humans to destroy obstacles that prevent them from achieving their goal Sadness encourages humans to seek comfort

5. B IOLOGICAL M ODELS F OR E MOTION Researchers in various fields related to AI attempt to reproduce different aspects of biological creatures to simulate adaptive behaviours An emotional component is often hard-coded. With this approach, the designer can impose biologically accurate emotions (for instance, fear, pain, and pleasure) and test their role in the learning. Complementary emotions can be considered as extreme values of a single variable, used to drive the learning toward positive emotions An adaptive component provides the ability to learn behaviours dynamically during the simulation. Techniques such as neural networks allow the creature to adapt to its emotional status and behave in a better fashion

6. H UMAN / M ACHINE I NTERACTION Emotions are certainly a defining characteristic of all mammals, and particularly humans They play a crucial role in the interaction between people. By designing our AI to exhibit more human emotions and characteristics we can improve the player’s interaction with our game The portrayal of emotions in synthetic creatures requires more than just AI. The fields of modelling, animation, linguistics, and speech synthesis are key aspects of the development

7. H UMAN / M ACHINE I NTERACTION Humans communicate emotions in a wide variety of ways. We can attempt to convey artificial emotions in the following forms: Expressions — Static facial expressions carry a tremendous amount of information about emotions (for instance, smile or frown). In fact, by analysing facial expressions we can distinguish between primary emotions Gestures — Body language and gestures are also strong indications of emotions. For example, slouching is a sign of depression, and nodding shows acceptance Behaviours — Over longer periods of time, behaviours are stronger manifestations of emotional state. For example, ignoring someone is a sign of rejection, taking care of people shows affection Language — The choice of words is an extremely strong indication of mood during a conversation (for instance, familiar or formal). Rhythm in sentences also conveys emotion; shorter sentences are more authoritative and sound angrier Voice— The tone of the voice the sentence is pronounced with also reflects mood. Loud voices indicate anger, faster speech often implies anxiety

8. E MOTIONS I N G AMES Failing to accomplishing a task can almost be considered as a bug in the game AI (for instance, running into a wall). Reactive behaviours can solve such problems without the need for solutions inspired by emotions On the other hand, when an agent is fully functional, the problem is increasing the levels of realism Emotions can help tremendously with this by enhancing the quality of the behaviours with a biologically plausible approach. There's particular interest in the following features that emotions will bring to games: Attachment — Individual characters that can display moods are more believable, and human players become emotionally attached to them. Such bonds can be strong enough to change the course of the game Storylines — By providing non-player characters with emotions, their interaction with humans is greatly improved. The essence of story lines happens between players, so emotions can greatly enhance the entertainment Immersiveness — With emotions, all non-player character behaviours would seem more realistic and generally increase the immersiveness of the game environment

9. E MOTIONS Emotions arise from complex interactions between the body and the brain. Emotions begin in the body, influenced by stimuli from the environment (such as an explosion) The brain generally responds to these low-level perceptions, which translate into persistent characteristics of the creature (as fear) These emotions can potentially become visible externally via behaviours (running away)

10. S ENSATIONS All emotions in embodied creatures are initiated by sensations A sensation is an immediate reaction to a creature's current status By definition, sensations are experienced practically instantaneously, based on changes in the current situation Two factors may cause sensations: current perceptions (stimuli from the environment) cognitive activity (thinking) Surprise, Anticipation, Disgust, Attraction, Confusion, Discovery, Pain, Pleasure

11. P ERCEPTUAL S ENSATIONS Typically, a sensation is triggered by perceptions. The body detects stimuli from the environment, and the information causes an immediate reaction in the brain Health and armour lost Blood splat Sparks/explosion Object disappears Arriving lift Door opening Enemy presence Desirable object

12. C OGNITIVE S ENSATIONS Sensations may also be triggered by reactions to the mental state (for instance, knowledge of the world or other emotions). Here, basic processing of information in the brain causes the sensation For instance, surprise can be caused by an object not being present, when the agent thought it should be there Sensations based on cognition and perception have common traits: Both are triggered when a pattern is matched in the brain. With perceptions, this pattern is matched instantly based on sensory information. On the other hand, some cognition is necessary before a pattern develops in the brain (by thinking), which eventually engenders a sensation instantly when a pattern is matched

13. E MOTIONS C ONT. Sensations can be considered low level because they are instantaneous patterns. Higher-level trends arise from cognitive activity too. These are called emotions An emotion is a lasting characteristic of a person's state Emotions change relatively slowly over time (compared to sensations, which are instantaneous) For example, fear and anger are lasting emotions, so are joy and sorrow. The changes in emotions are generally triggered by the agent's sensations. An emotion could also correspond directly to a single sensation (for instance, surprise)

14. P ORTRAYING E MOTIONS I N G AMES The following list of scenarios illustrates the kind of emotion-driven behaviours that our agents could be capable of portraying: Jump, wave, or dance of joy Run faster with fear, simulating adrenaline rushes Stop thinking and freeze when affected by panic Diminish accuracy of all actions when boredom sets in (for instance, sleepiness, complacency) Turn away in disgust (for instance, blood splat), or focus on attractive other player Insult the enemies when they get killed, or perform a taunting gesture Run away scared when the enemy is more powerful Select the enemy to target from personal vengeance, based on past fight history

15. M ETHODS O F P ORTRAYING E MOTION Finite State Machines Advantages Finite-state machines are so incredibly simple. They're easy to implement, visualize, design, debug, and work with Their theory is extremely well understood. We have formal definitions of finite-state machines, which can be optimized and manipulated by various algorithms Finite-state machines have been proven to work well with computer games, and are in fact one of the most popular AI techniques. This is because of the fact that they can be used for control, and almost anyone can create them Disadvantages Designing finite-state machines can get very complex when building large machines They are computationally limited to certain problems The design of finite-state machines is frozen at runtime The output of finite-state machines is very predictable, and not necessarily suited to creating behaviours

16. D ESIGNING A RTIFICIAL E MOTIONS The design phase must decide which emotions are experienced by the agent, which sensations trigger changes in emotions, and how they are portrayed in the behaviour To start with we can only include the most important emotions. Namely: Fear and anger Surprise and anticipation As complementary emotions, only two of four may be observable at any point in time. Each of the emotions is defined as a binary value: either fully active or inactive.

17. E MOTION FSM

18. SurpriseAnticipation FearPrecision 0.7 Power 0.2 Delay 0.0 Accuracy 0.9 Precision 0.9 Power 0.4 Delay 1.0 Accuracy 0.2 AngerPrecision 0.0 Power 1.0 Delay 0.3 Accuracy 0.8 Precision 0.1 Power 0.9 Delay 0.8 Accuracy 0.3

19. E MOTION FSA

20. E MOTIONAL S YSTEM Memories gathered using statistics Feelings expressed as a nondeterministic automaton Sensations represented as fuzzy automata Emotions are fuzzy-state machines Mannerisms selected by nested probabilistic automata Moods modelled with nested states

21. E MOTIONAL S YSTEM

22. R EFERENCES AI Game Development: Synthetic Creatures with Learning and Reactive Behaviors Alex J. Champandard Publisher : New Riders Publishing ISBN : 1-5927-3004-3 Part VI: Emotions