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Mental State

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 gif 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):

eqnarray1383

where

t is time,
tex2html_wrap_inline3404 is the amount of food consumed as measured by the number of food particles or prey fishes eaten,
tex2html_wrap_inline3406 with constant tex2html_wrap_inline3408 is the digestion rate,
tex2html_wrap_inline3410 is the time since the last meal,
tex2html_wrap_inline3412 is a constant that indicates the appetite of the fish (bigger fishes have a larger tex2html_wrap_inline3412 ),
tex2html_wrap_inline3416 captures the influence of external sensory stimuli, i.e. the perception of nearby food (explained in more detail shortly),
tex2html_wrap_inline3418 with constant tex2html_wrap_inline3420 is the libido function,
tex2html_wrap_inline3422 is the time since the last mating,
tex2html_wrap_inline3424 calculates the influence of the perception of potential mates;
tex2html_wrap_inline3426 is a constant,
tex2html_wrap_inline3428 and tex2html_wrap_inline3430 are, respectively, the fear of and distance to sighted predator i.

Nominal constants are tex2html_wrap_inline3434 and tex2html_wrap_inline3436 . Certain choices can result in ravenous fishes (e.g, tex2html_wrap_inline3438 ) or sexual mania (e.g., tex2html_wrap_inline3440 ) or cowards (e.g., tex2html_wrap_inline3442 ).


next up previous contents
Next: Opportunism Up: The Behavior System Previous: Habits
Xiaoyuan TuJanuary 1996