Because this is covered in the other tutorials, I won't say much about it here. Levels of detail in neural modelling varied then and still do: the neurons of Grey Walter's turtles tried to be more biologically realistic than those of the perceptron. It's worth noting that there are now many varieties of connectionism. The back-prop net is not representative of them all, so don't assume that all connectionist systems share the same properties and limitations. The AI photocopy box contains articles on a variety of systems.