To enable an artificial animal to behave realistically and autonomously, it is necessary to model relevant aspects of its habitat as well as its internal mental state. Sensory stimuli present information about environmental events such as the presence of food, which may cause the animal to ingest, or the presence of a predator, which may cause the animal to flee. However, external stimuli alone cannot fully determine an animal's behavior. An animal that is satiated will normally not ingest more food even if food is available. If an animal is desperately thirsty, it may delay taking evasive action despite the presence of a predator in the distance in order to drink at a waterhole. Its decision to engage in a particular behavior is predicated on the internal state of the animal which reflects the physical condition of its body--whether it is hungry, tired, etc. Such internal state can thus be considered as inducing the ``need'' or ``motivation'' to evoke a specific behavior.
|Xiaoyuan Tu||January 1996|