Page 79 - Foundations of Cognitive Psychology : Core Readings

78 Jay L. McClelland, David E.Rumelhart, and Geoffrey E.Hinton

Figure 4.11
Some of the units and interconnections needed to represent the individuals shown in figure 4.10.
The units connected with double-headed arrows are mutually excitatory.All the units within
the same cloud are mutually inhibitory.(From ‘‘Retrieving General and Specific Knowledge from
Stored Knowledge of Specifics’’ by J.L.McClelland, 1981, Proceedings of the Third Annual Confer-
ence of the Cognitive Science Society, Berkeley, CA. Copyright 1981 by J.L.McClelland. Reprinted by
permission.)

more to say about this simple model, for like some of the other models we have
already examined, this model exhibits some useful properties which emerge
from the interactions of the processing units.
Default Assignment It probably will have occurred to the reader that in many
of the situations we have been examining, there will be other activations oc-
curring which may influence the pattern of activation which is retrieved.So, in
the case where we retrieved the properties of Lance, those properties, once they
become active, can begin to activate the units for other individuals with those
same properties.The memory unit for Lance will be in competition with these
units and will tend to keep their activation down, but to the extent that they do
become active, they will tend to activate their own properties and therefore fill
them in.In this way, the model can fill in properties of individuals based on
what it knows about other, similar instances.
To illustrate how this might work we have simulated the case in which we do
not know that Lance is a Burglar as opposed to a Bookie or a Pusher.It turns
out that there are a group of individuals in the set who are very similar to
Lance in many respects.When Lance’s properties become activated, these other
units become partially activated, and they start activating their properties.