A new approach to NPC behavior simulation: The Mask Model

1. A new approach to NPC behavior simulation: The Mask Model Francesco Osborne Computer Science Department, University of Torino, Italy (at the moment in KMi, Open University, UK)

2. Outline • The approach • The mask • Profile based on mask layers • Choosing an action

3. Addressed problem • NPC behavior is usually weakly correlated to her or his social and cultural environment and to other character's presence and expected behavior.

4. The mask concept I • Humans tend to exhibit a social performance that leads them to play different roles in different situations.

5. The mask model • It is useful to introduce the concept of mask that NPCs can wear and be influenced by. • The mask model aims at generating realistic and socially driven actions for the common NPC's and inducing a more flexible behavior for the significant ones. • This approach can be applied to many kind of already existing NPC.

6. The mask Reference Entity Attribute overlay Tendency rules Permanent links Temporary links Role : level of inf. Role : level of inf. Role : level of inf. Role : level of inf. Role : level of inf.

7. Linking Marks and Characters • A character can be linked to more then one mask which represent the different entity which influence the character. The link that connects a person to a mask is associated with two values representing: • the character role • and the level of influence that the mask exerts on the character.

8. The role • The role is needed to discriminate among the behavior expected from different kinds of characters.

9. The role • A character may have more than one role for the same mask and the role can contain a reference to an entity that we call role entity. • Example: if Bill is husband->Ann Some suggested reactions to Bill's actions could involve Ann.

10. The level of moral influence • The level of moral influence can be thought as a value between 0 and 1 which describes how much the mask affects the morality of a person.

11. The level of moral influence • The level of moral influence can be thought as a value between 0 and 1 which describes how much the mask affects the morality of a person. • If the mask represent a religion, a low value would describe a moderate believer, a high value would point to a fanatic ready to kill for it.

12. Attribute overlay Reference Entity Tendency rules Permanent links Temporary links Role : level of inf. Role : level of inf. Role : level of inf. Role : level of inf. Role : level of inf.

13. The reference entity • The reference entity can be a government, a religion, a group of people with a common ideology or a single person or even the character itself.

14. The overlay on the profile • The overlay allows the change of some characteristics of the characters. It will obviously depend on the type of character profile. • Example: in an implementation that takes into account various psychological components associated with an intensity (like "Prom Week”), a mask can change these values in an absolute or relative way.

15. Tendency rules I • A tendency rule is expressed in the form: rule id - affected roles : {precondition -> action(entity)} : strength • If a character have a certain role, when the pre-conditions are triggered, an action on a entity is suggested with a certain strength.

16. Tendency rules II - Strength • Each tendency rule is associated with the rule strength which reflects the significance of the rule for the reference entity and is represented by a value between -1 and 1.

17. Aspected social reaction • It is also important to notice that a character has usually access to the rules denoting the other character roles.

18. Activation condition • Each character has some persistent masks and may further be subjected to the influence of masks activated by the environment.

19. The mask layers • The character tendencies are controlled by the interactions of three overlapping mask layers: • Self-perception layer • Social layer • Inter-personal layer

20. Bill

21. Self-perception layer Bill

22. Self-perception layer Bill Self Perception Bill

23. Self-perception layer • The self-perception layer consists of a single mask that represents the idea that a character has of himself.

24. Self-perception layer • The self-perception layer consists of a single mask that represents the idea that a character has of himself. • It is useful to modulate the deepest trends of a character and is also needed to model elusive concepts as self-deception.

25. Self-perception layer • The self-perception layer consists of a single mask that represents the idea that a character has of himself. • It is useful to modulate the deepest trends of a character and is also needed to model elusive concepts as self-deception. • This mask is always active.

26. Self-perception layer Social layer Bill Self Perception Bill

27. Self-perception layer Social layer Bill Self Perception Bill Religion X Political party Y USA culture

28. Social layer • The social layer is the set of all the masks which represent: • the beliefsof a person • his respect for the rules of the social environment.

29. Self-perception layer Social layer Bill Self Perception Bill Religion X Political party Y USA culture

30. Self-perception layer Social layer Bill Self Perception Bill Religion X Italy culture Political party Y USA culture

31. Self-perception layer Social layer Interpersonal layer Bill Self Perception Bill Religion X Italy culture Political party Y USA culture

32. Self-perception layer Social layer Interpersonal layer Bill Self Perception Bill Ann (girlfriend) Religion X Italy culture Cindy (mother) Political party Y USA culture

33. Inter-personal layer I • The inter-personal layer collects all those masks that have as reference entity another character. They may be: • persistent • activated only in the presence of a particular character.

34. Self-perception layer Social layer Interpersonal layer Bill Self Perception Bill Ann (girlfriend) Religion X Italy culture Cindy (mother) Political party Y USA culture

35. Self-perception layer Social layer Interpersonal layer Bill Self Perception Bill Ann (girlfriend) Religion X Italy culture Cindy (mother) Political party Y Dave (boss) USA culture

36. Challenges The main problems to address in this model are: • Managing conflicts between masks • Managing the selection of an action • Simulating the human cognitive processes

37. Solving conflicts I • In the BDI architecture it is common to have different plans that can accomplish a goal and the criterion for choosing them is often left to individual implementations. • For example, if the goal is "obtain 100 gold coins" we can do that in many ways.

38. Solving conflicts II

39. Solving conflicts III • In our approach the agent should look at the different paths leading to different goals and execute the one which has the greatest likelihood for him in a certain social context. • This requires the evaluation of both rational and emotional/ethical aspects. This can lead to irrational behaviors.

40. Solving conflicts IV To calculate the likelihood of an action I propose a two-step mechanism: • The weight of the pros and cons • The weight of the perceived moral soundness of the action

41. Weight of the pros and cons • The weight of pros is performed by estimating the gainthat a certain action will bring to the character. • However we should take into consideration two types of gain: • the direct one • the ensuing one.

42. Weight of the pros and cons • The first include the immediate benefits or harms obtained through an action.

43. Weight of the pros and cons • The second are the benefits or damages resulting from the actions that can be set in motion by the tendency rules which suggest a reaction to the original behavior.

44. Visibility I • Any action performed in the world will be visible to some entity and unknown by others. • Visibility can be expressed as a percentage that reflects the probability that the reference entity will discover a certain action.

45. Reaction Probability • The probability that a entity will decide to react to the initial action. • For example: The probability that a policeman may decide to arrest a theft after learning of the violation. • It depend on the strength of the tendency rule and the environment.

46. Relative strength • The estimate of the relative strength of an entity is the measure of its possibility to inflict a punishment after learning of the violation.

47. Relative strength • The estimate of the relative strength of an entity is the measure of its possibility to inflict a punishment after learning of the violation. • It depends on the balance of powers between characters within a given environment.

48. Ego-esteem • Combining the concept of gain g, visibility of the initial action, the reaction probability and the estimation of success of the ensuing action, it is possible to calculate the pros and cons of an action, obtaining E(action) = ag +(1- a) • a is a measure of the character impulsivity and varies from 0 to 1.

49. Weight of the moral soundness This weight depends on both: • The influence of the masks on the character • The strength of the tendency rules The first value reflects how much a character is influenced by a given entity, the second value how important is the tendency rule.

50. Super-ego-esteem S(action)= • where ri is the strength of the i-th rule and mi is the influenceof the relative mask. • If the action is contrary to the tendency rule, the ethical importance factor will become negative.