Details about the artificial intelligence feature in S.T.AL.K.E.R. have been posted to HomeLAN Fed:

In real life all the living creatures require feed and rest. So as in our world the sense of hunger flogs a creature to seek food, and the acuter is hunger, the more aggressive the monster becomes. After satiation the animal either gets to rest – sleeps therefore, or sets off to inspect his territory. All the character types have their personal territorial preferences. Thus, for instance, rats prefer basements, ruins or dumps, while blind dogs adore roaming down valleys and forests. During the look-out there may be encountered an aggressor – a hostile creature or stalker. Then, depending on circumstances, the creature will decide whether to attack or clear out.

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More info:
Official site
GSC Game World
S.T.A.L.K.E.R. – 16 New MP Videos (28 Dec 2004)
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