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Opportunism

 

The significance of simulating explicitly the influence of external stimuli on H and L is that it gives rise to opportunism. Opportunism is an important aspect of animal behavior and has been especially addressed by researchers in designing action selection mechanisms for animats [Maes1990, Maes1991a, Sahota1994]. We model opportunism to increase the realism of the behavior of the artificial fishes.

It is reasonable to assume that the mental state of hunger and libido are governed mainly by the corresponding internal urge, while external stimuli will have an impact only if they are strong enough. This indicates that tex2html_wrap_inline3450 and tex2html_wrap_inline3452 should resemble a step function. The detailed calculations are as follows. For efficiency, we assume that only the stimulus of the closest food and mate contributes to tex2html_wrap_inline3450 and tex2html_wrap_inline3452 , respectively. In addition, the strength of such a stimulus depends solely on the time-varying distance d(t) between the stimulant and the fish--the smaller the d(t), the stronger the stimulus. Let s(t) = 1/d(t) denote the strength of the stimuli, then tex2html_wrap_inline3450 and tex2html_wrap_inline3452 are given by

displaymath3444

where x denotes either h or l and tex2html_wrap_inline3478 , tex2html_wrap_inline3480 are threshold values. When x=`h', we use tex2html_wrap_inline3486 and tex2html_wrap_inline3488 ; When x=`l', we use tex2html_wrap_inline3494 and tex2html_wrap_inline3496 . A graph of tex2html_wrap_inline3450 and tex2html_wrap_inline3452 is shown in Fig. gif. The parameters are tex2html_wrap_inline3502 and tex2html_wrap_inline3504 in our implementation.

   figure1408
Figure: The form of the stimulus functions tex2html_wrap_inline3450 and tex2html_wrap_inline3452 .


next up previous contents
Next: Satiation of a Desire Up: Mental State Previous: Mental State
Xiaoyuan TuJanuary 1996