GAMYGDALA is an emotion assessment engine which allows game developers to add emotions to Non-Player Characters (NPC). Designing NPCs behavior are a very important challenge that game developers and designers face. After players have played the game for some considerable amount of time the behavior of the NPCs becomes quite predictable, making it boring. Emotional expression and emotional behavior can add variation to the NPC, but what emotion to express and when is also a challenge.
GAMYGDALA proposes an emotion engine where the solution is positioned between the event coding of affect where individual events have predetermined annotated emotional consequences for NPCs. Therefore, an NPC that needs emotion the game developer defines goals and adds a game event to that specific goal. On the basis of this input GAMYGDALA produces an emotion for that NPC. Different NPCs can thus react differently to the same situation, and the same situation can bring different emotions in the same NPC depending on its active goals. Emotional reactions can depend on previous events that changed the goals of an NPC but GAMYGDALA itself does not include memory.
GAMYGDALA is coined from ‘amygdala’ which a part of the brain highly responsible for emotions It is a computational model that recognizes which emotion fits an NPC during a particular event, in a way that it is consistent with the current phycological knowledge and storyline of the game. The advantage of using GAMYGDALA is that the game designer gets plausible emotions without having to design them and without having to specify them for each event. Yet GAMYGDALA does not have the computational costs of a full-blown emotional AI engine which also includes reasoning and planning. GAMYGDALA allows simulation of up to 35,000 NPCs, 2 goals and beliefs per NPC, with a total computing time of less than one second. This computing time includes 70,000 belief additions, and a final emotion computation.
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Basic emotions and social emotions are supported by GAMYGDALA, enabling the developer to create wide range of emotional states. It is based on the model of Ortony, Clore and Collins (OCC).
The authors relate to theories they based their work on, first is Emotion theory which defines a set of basic emotions and each emotion is characterized by feelings, expression and behavior. But just characterizing each emotion was not the motive, their interest is in simulating the emotions in NPCs and to achieve that they need to know how events in the game result to emotions, for which they turn to cognitive appraisal. Cognitive appraisal theory assumes that an emotion is the result of a cognitive process. Here the person is constantly assessing the events taking place around him or her and then these events are evaluated in terms of relevant and helpful they are to that person and other person’s goals.
This theory is more related to concepts of goals rather than dealing with if and how opposing emotions cancel each other or how multiple emotions form an emotional state. Although OCC theory proposes the listed emotions as being emotion types and reject the idea of basic emotions. The authors have defined 24 emotions in all that are associated with several evaluative components. The authors decide to use OCC as basis for their emotion engine as it is a well-known and accepted theory of emotions, it is a componential model of emotion that fits the needs of a computational framework.
The authors argue that GAMYGDALA is indeed easy to use, AI independent and easily pluggable. The only thing that is then needed is to annotate some game events with goal congruence that is how good or bad is this event is and for which goal. To use GAMYGDALA, a game designer needs to explicitly define one or more goals for each NPC. The game designer can now define which type of events are relevant to each goal and specify this in GAMYGDALA. The only essential modification to a game is that events delivered to the game AI controlling the NPC’s behavior are also delivered to GAMYGDALA.
GAMYGDALA emotionally appraises the event and outputs the most plausible emotions based on the OCC model. This way of using an emotion engine is analogous to how physics engines are used. This approach is AI independent. Nowhere a link to the AI system is needed for emotion simulation, even though some AI mechanisms might interface more naturally with GAMYGDALA including BDI-based goal-oriented reasoning and planning. GAMYGDALA is a richer model for generating emotions than event coding. GAMYGDALA finds emotions for the NPCs. The game developer can use this to add expression or emotional behavior.
Towards the end of the paper there are examples and evaluations of GAMYGDALA, that how it is used with games and game AI. The given examples are simple arcade game, role playing game (RPG), First Person Shooter (FPS) and Real Time Strategy (RTS). These examples represent different game genres with different NPCs.
