Units and activation levels
Pages 5

The activation level of a unit corresponds to the idea of the degree of activation of some cognitive element represented by the unit (discussed further below). The activation of a single unit is represented by a single number, most commonly having a value from 0 to 1. An activation value of 0 means that the unit is not active at all; an activation value of 1 means that it is as active as it can possibly be. We will symbolize the activation levels of units with the letter a, with subscripts to denote the activations of particular units. For instance, the activation of two arbitrary units, ui and uj, have associated activation levels ai and aj. The activations of whole set of units, say the output units of a network, can be represented as a set of numbers, e.g. {a1, a2, . . ., an} for an arbitrary number (n) of units. In this case it is generally more convenient to use vector notation, described below.