Paper: A connectionist model of recursion

[Morten Christiansen]

A preprint of the following paper to appear in Cognitive Science is
available at

	http://www-rcf.usc.edu/~mortenc/nn-rec.html


	Toward a connectionist model of recursion 
	      in human linguistic performance

                     Morten H. Christiansen
                University of Southern California

                           Nick Chater
                      University of Warwick


                            Abstract 

Naturally occurring speech contains only a limited amount of complex
recursive structure, and this is reflected in the empirically documented
difficulties that people experience when processing such structures.  We
present a connectionist model of human performance in processing recursive
language structures. The model is trained on simple artificial languages. 
We find that the qualitative performance profile of the model matches
human behavior, both on the relative difficulty of center-embedded and
cross-dependency, and between the processing of these complex recursive
structures and right-branching recursive constructions.  We analyze how
these differences in performance are reflected in the internal
representations of the model by performing discriminant analyses on these
representation both before and after training. Furthermore, we show how a
network trained to process recursive structures can also generate such
structures in a probabilistic fashion. This work suggests a novel
explanation of people's limited recursive performance, without assuming
the existence of a mentally represented competence grammar allowing
unbounded recursion. 


--Morten Christiansen

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Morten H. Christiansen, Ph.D.     | Phone: +1 (213) 740-6299
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