Modeling Hydra Behavior Using Methods Founded in Behavior-Based Robotics

7.1. Generation of behaviors 35Table 7.2: EA properties for the best evolved cascaded integrators habituation unit.Population size 100Initial model size 5 unitsTournament size 10p cross 0.5p tour 0.70p mut1 0.10p mut2 0.05Parameter range (a,b) [0, 1]The best model obtained consists of 10 units, the parameter values of which are givenbelow.a = ( 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.998 0.003 )b = ( 0.124 0.010 0.105 0.012 0.711 0.204 0.107 0.549 0.004 0.010 )Transfer functionThe transfer function is initialized when the AC is set, and its task is to generate a CP oran LP. One problem with determining whether locomotion or contraction is the adequateresponse is that only qualitative descriptions of this relationship were found in the literature[28, 45, 46]. These descriptions implies that there is a relative increase in locomotionresponses in starved animals. Here, the following relationship was used to determine theresponse typef con = a con ,f loc = a loc M h , (7.9)for 0 < M h < h max . If M h = h max , neither a CP nor an LP is evoked. Here, a conwas set to 300 and a loc to 0.001. The probability of locomotion and contraction response,respectively, was taken asp con =p loc =f con,f con + f locf loc. (7.10)f con + f locThe constant latency was set to 2 s, the duration of a CP to 10 s, and the duration of anLP to 60 s. Fig. 7.6 shows an example of the output from the transfer function during acontraction response to mechanical stimulus. The AC, being of set/reset character, causesthe behavioral output to be active between the time of set and reset.