Unlike a fish's habits, which are static, its mental state varies over time. The mental state of an animal can be viewed as consisting of several distinct desires. For example, the desire to drink or the desire to eat. In order to model an artificial fish's mental state, it is important to make certain that the modeled desires resemble the three fundamental properties of natural desires: (a) they should be time varying; (b) they should depend on either internal urge or external stimuli or both; (c) they should be satisfiable (see Section for more details).
Currently, the artificial fish has three mental state variables, hunger H, libido L, and fear F. The range of each variable is [0,1], with higher values indicating a stronger desire to eat, mate and avoid predators, respectively. H and L are determined both by internal urge and by external sensory stimuli, while F is solely induced by the latter, i.e., the perception of predators. The variables are calculated as follows (overlined terms simulate the corresponding internal urge):
|Xiaoyuan Tu||January 1996|