Axel Cleereman has designed a learning tool to illlustrate activiation and competition in Rumelhart and McClelland's parallel distributed processing connectionist model as described in McClelland, J.L. (1981).
Read Cleereman's introduction and visit the website
Note especially the explanation of the network:
The model captures what someone might know about characters inspired from the 1961 musical "West Side Story", in which two gangs (the "Jets" and the "Sharks") fight for territory and overall dominance. Units, the activation level of which represents the fact that the feature they stand for is true to some degree, are organized in separate groups, each corresponding to the different possible values of a single feature, such as the name of an individual, his age, his education level, his marital status, his occupation, or the gang to which he belongs.
and instructions for playing
To explore the model, simply click on any unit to activate it, and watch the model progressively settle in a state in which only a few units - those that represent features that are most compatible with your input - remain active.
See another example of neural networks related to language learning.