Thesis - Department of Electronic & Computer Engineering

served, as some loser will never stop firing, although it fires sparsely. Consequently, itswitches to WSA behavior.It also shows that asT pdecreases, the intersection points shift to the left, that is,both θ l( T p) and θ h( T p) also decreases till at last θ h( T p) →θ mand θ l( T p) → 0 .Therefore, the range of the available threshold shifts to the left asT pdecreases. Alsowhen T p« 1 , the applicable range of the threshold can be approximated by ( 0,θ m).Because of the assumption of the whole analysis, the above constraints are necessarybut not sufficient.At this point, it seems appropriate to stress that, the relative strength of self-excitationand lateral inhibition is crucial to the competitive behavior of the network.We keep a + b = 1 constant and choose b = 0.4, 0.5,0.6 respectively. Fig. 5.8shows that θ h( T p) increases as b decreases. That is, the constraints on the thresholdaais loosened as -- increases. This is straightforward, the ratio, -- , determines the degreebbof WTA behavior. The larger the ratio, the harder the WTA, the weaker the constraintson the threshold selection.48