Artificial Intelligence

Artificial Intelligence (AI) raises the computer character above the level of digital puppet to that of synthetic actor. It allows the synthetic actor to make decisions to vary and adjust their performance and behaviour, in response to internal and external factors, while introducing randomising factors where appropriate to avoid the appearance of deterministic, robotic behaviour and to simulate imperfect decision making. AI techniques can also be used by synthetic actors to express procedurally encoded or recorded emotions to imitate human or other animal emotions or to suggest physical or physiological characteristics or behavioural responses. Often the sort of AI one encounters in games is called Applied or Soft AI and distinguished from General or Strong AI, that is equal to or better than human intelligence, the type that is the ultimate goal of AI research.

There are various forms of Applied and Hard AI: problem solving (path-finding), emotional (expressive and interpretive), social (cooperative), physical (controlling our own physical movements and moving external objects). Mimicking the various kinds requires different synacting approaches.

Navigation involve Pathfinding, steering and smoothing, in dynamic and static environments. A dynamic environment may result from change of position of existing obstacles, or newly introduced obstacles or additional agents on collision courses with each other.

The agent shows intelligence in when to move, where to move, how fast to move, in its manner of movement. The actor can also exhibit signs of intelligent design in discernable consequences of its actions: signs of breathing faster during and after exertion, effect on speech prosody, sweating, skin colour changes (face reddening) or in the effect of its emotional state on the manner of its actions. These signs of physical intelligence extend also to how the body shifts its centre of gravity or adjusts movements to reflect local impacts due to the ground, the air, or other objects collided with under any notional gravity. The agent indicates intelligent natural human motion in anticipating movements with its eyes and/or head momentarily before making the movement. Intelligence is evident also in speaking, by including conversational prosodic signs, gestures and assymetrical posturing (contraposto). Flocking behaviours of alignment, cohesion and avoidance. It is important also for agents not to move together in a wholly synchronous way but in a way that suggests individuality or adjusting to variations in the immediate environment, even if this means cheating.

Note that exhibiting intelligent behaviour may require different types of intelligent decision-making to be combined. For example, when calculating the shortest path between two points, the spaces between individuals engaged in conversation should be treated in a special way. To enter such a space would be impolite, so to avoid it shows social intelligence. If entering the space is unavoidable, then pardoning yourself can be expected, and if excuses aren't forthcoming, those interrupted demonstrate social intelligence by appropriately acknowledging the interruption. To date (2011) NPC (synactor) crowd extras have very limited behaviours in games. Assassin's Creed extras do tend to behave in relatively sophisticated ways. In Just Cause 2 extras either go about their business or, when the shooting starts, assume a crouched, cowering stance and may or may not run-away. As soon as the shooting stops however, the threatening event is erased from their memory and they continue as normal. In Saboteur, for example, social groups of extras are oblivious to the player character's actions. Inflexibility in the behaviour of NPC extras severely compromises the believability of synactors' performance, breaking the player's theatrical immersion by provoking a Truman moment.

Sometimes programmers create problem-solving solutions that work in the digital realm with consequences that suggest scientific laws operating outside the digital world are being contradicted. For example, characters can be seen to interpenetrate and move through other objects, including interpenetrations between their own body parts and clothes; they appear weightless (basically, because they are!).