Work

Sharks and Jets

06 Oct 2008, 07:31 PM

I finally got around simulating the classic Sharks and Jets experiment using Cell Assemblies (CAs).

The Sharks and Jets experiment [McClelland, 1981] was designed to demonstrate how a network could function as a content-addressable memory system. The information to be encoded was two groups (Sharks and Jets), group members
and some demographic attributes of theirs. The goal of the experiment was to store, associate and retrieve patterns in a network.

My CA implementation of the model learned, grouped and associated members of a group. Associations between different patterns were defined as overlapping neurons in the CA network. The associations were learnt through a series of cycles. The model was tested by presenting a randomly chosen pattern of all the ones learnt. For instance, when a member of a group was presented, activation was observed in that member and the areas of his demographic characteristics. When a parent group was presented, activation was observed in a large scale where many members of that group and their attributes ignited and in many cases, a particular member had the most activation, assumed to be the prototypical representation of that group.

While the network in the original experiment was specialised to the goal, the CA implementation was conducted based on the general behaviour of CAs (having distance biased neuron connections). Even though the highly interesting dynamics observed in the original experiment were not recreated in the implementation, the goal of observing associative behaviour in CAs was attained with fair success.

[McClelland, 1981] McClelland, J. L. (1981). Retrieving general and specific information from stored knowledge of specifics. In Proceedings of the Third Annual Conference of the Cognitive Science Society, pages 170–2.