Connectionist symbol processing : dead or alive ?
Preface In August 1998 Dave Touretzky asked on the connectionists e-mailing list, \Is connectionist symbol processing dead?" This query lead to an interesting discussion and exchange of ideas. We thought it might be useful to capture this exchange in an article. We solicited contributions, and this collective article is the result. Contributions were solicited by a public call on the connectionists e-mailing list. All contributions received were subjected to two to three informal reviews. Almost all were accepted with varying degrees of revision. Given the number and variety of contributions, the articles cover a wide, though by no means complete, range of the work in the eld. The pieces in this article are of varying nature: position summaries, individual research summaries, historical accounts, discussion of controversial issues, etc. We have not attempted to connect the various pieces together, or to organize them within a coherent framework. Despite this, we think, the reader will nd this collection useful. Implementing symbol processing in networks was a good rst step in solving many problems that plagued symbolic systems. Tony Plate's HRR as applied to analogy is a great example 147]. Using connectionist representations and methodologies, an expensive symbolic similarity estimation process was eliminated in the analogy-making MAC/FAC system 60]. Unfortunately, the entire MAC/FAC hybrid model (like many such models) has a fatal aw that prevents it from leading to an autonomous, exible, creative, intelligent (analogy-making) machine: the overall system organization is still rigidly \symbolic". Their method requires that analogies be encoded as symbols and structures, which leaves no room for perception or context eeects during the analogy making process (for a detailed description of this problem, see Hofstadter 86]). For these reasons, implementing Gentner's rigid framework completely in a neural network (or even real neurons) won't help. Plate's hybrid solution, like most hybrid systems, solved many problems of the MAC/FAC purely-symbolic system. No doubt, hybrid systems are better than their symbolic relatives. However, wherever symbols and structures remain, we seem to be faced with other problems of brittleness and rigidity.