TR: Understanding Normal and Impaired Word Reading

[David Plaut]

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		Understanding Normal and Impaired Word Reading:
	       Computational Principles in Quasi-Regular Domains

	     David C. Plaut                    James L. McClelland
	Carnegie Mellon University          Carnegie Mellon University

	    Mark S. Seidenberg                 Karalyn E. Patterson
      University of Southern California     MRC Applied Psychology Unit

			 Technical Report PDP.CNS.94.5
				   July 1994

We develop a connectionist approach to processing in quasi-regular domains, as
exemplified by English word reading.  A consideration of the shortcomings of a
previous implementation (Seidenberg & McClelland, 1989, Psych. Rev.)  in
reading nonwords leads to the development of orthographic and phonological
representations that capture better the relevant structure among the written
and spoken forms of words.  In a number of simulation experiments, networks
using the new representations learn to read both regular and exception words,
including low-frequency exception words, and yet are still able to read
pronounceable nonwords as well as skilled readers.  A mathematical analysis of
the effects of word frequency and spelling-sound consistency in a related but
simpler system serves to clarify the close relationship of these factors in
influencing naming latencies.  These insights are verified in subsequent
simulations, including an attractor network that reproduces the naming latency
data directly in its time to settle on a response.  Further analyses of the
network's ability to reproduce data on impaired reading in surface dyslexia
support a view of the reading system that incorporates a graded
division-of-labor between semantic and phonological processes.  Such a view is
consistent with the more general Seidenberg and McClelland framework and has
some similarities with---but also important differences from---the standard
dual-route account.

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David Plaut			plaut at cmu.edu	      "Doubt is not a pleasant
Department of Psychology	412/268-5145	       condition, but certainty
Carnegie Mellon University	412/268-5060 (FAX)     is an absurd one."
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