PARALLEL, INTERCONNECTED NEURONS 17 



ism by which the stronger of two simultaneous stimuli elicits its ap- 

 propriate response and prevents the other response. If, further, 



a 1 = S 1 - S 2 + (h' -h), 



and if, finally, h' and h are very nearly equal, the transmitted stimu- 

 lus approximates the absolute value of the difference between the 

 two stimuli. 



More generally, let the excitatory neuron N H connect s, with 

 s'i (i== 1 , ••• , n) (Figure 4), let the inhibitory neuron Na(i ¥= j) con- 



N11 N, 

 S^^—^ , ^^ .jt> 



So> <L^ U - VT » ^r^H > ' 



2 — ><^^—""« 





*-""Va . -> 3 ^^_?j3. 



Figure 4 



nect St with s'j and let a , — ft , h , li and ft" be the activity parameters 

 and the thresholds of the various neurons. If all neurons of the first 

 level are active, 



Vi = a(Si-h) -/J2 (Sj-h f ) , (6) 



and the conditions for excitation of N\ (originating at s\) is oi > h". 

 If h < h', then for values of the Sj between h and h' the excitatory but 

 not the inhibitory neurons are excited. If, further, 



a(h' -h) >h" , (7) 



then for values of the Sj near h' the neurons Ni are all excited. But 

 with 



n > 1 + a/0 , (8) 



when all the Si are equal, the <n are equal, and if 



P(n-l)h' - ah-h" 



S^ , (9) 



(w-1) 0-a 



none of the Ni responds, though for somewhat smaller values of £ 

 they all respond. 



With the same relations among the parameters, suppose the Si 

 are not all equal, but that each exceeds h' . It is no restriction to sup- 

 pose that 



