Connectionism and the problem of multiple instantiation

Multiple instantiation is the ability to handle different instances of the same concept simultaneously. For example, from the following two facts: `Pepin the Short was the son of Charles Martel' and `Charlemagne was the son of Pepin the Short', one can infer that Charles Martel was the grandfather of Charlemagne. This inference requires two instantiations of `Pepin the Short', the first in the role of son, the second in the role of father. For a connectionist model that does not use a working area receiving copies of items from a long-term knowledge base, the problem of multiple instantiation is a particularly thorny one. People are able to deal with multiple instances, unlike most connectionist models, but nonetheless their performance when doing so is reduced. On the other hand, there is no decrease in performance for symbolic models doing multiple instantiation. A good cognitive model should reflect both human competence and human limitations. This review proposes several connectionist solutions to the problem of multiple instantiation and examines their merits.