Computation in Neural Nets - Understanding Understanding: Essays on Cybernetics and Cognition - page 37

vi) The internal state Z of the neuron is defined by

Â

Zn ii = - q. (15)

vii) The single output Y is two-valued, either ON (1) or OFF (0)

( y = 0, 1) and its value is determined by

0 for
1 for

Z
Z

<-
>-

e
e

,
,

Ó

= () =

y F Z

where e is a positive number smaller than unity:

0

<< e 1 .

The i th fiber will be denoted by a capital X i , while its state by a lower
case x i .

viii) The neuron requires a time interval of D t to complete its output.

We shall briefly elucidate these rules with the aid of fig. 9 which is a sym-
bolic representation of this element. The neuron proper is the triangular
figure, symbolizing the perikaryon, with a vertical extension upward receiv-
ing inhibitory fibers, each loop representing a single inhibitory synaptic
junction. Excitatory junctions are symbolized as terminal buttons attached
to the perikaryon. In fig. 9 the number of input fibers is:

N = 4,

FIGURE 9. Symbolic representation of a
McCulloch formal neuron.