Preprint: Modularity and double dissociations in damaged networks

[David Plaut]

		    Double Dissociation Without Modularity:
		  Evidence from Connectionist Neuropsychology

				David C. Plaut
			   Department of Psychology
			  Carnegie Mellon University

       To appear in Journal of Clinical and Experimental Neuropsychology
		   Special Issue on Modularity and the Brain

Many theorists assume that the cognitive system is composed of a collection of
encapsulated processing components or modules, each dedicated to performing a
particular cognitive function.  On this view, selective impairment of cognitive
tasks following brain damage, as evidenced by double dissociations, are
naturally interpreted in terms of the loss of particular processing components.
By contrast, the current investigation examines in detail a double dissociation
between concrete and abstract word reading after damage to a connectionist
network that pronounces words via meaning and yet has no separable components
(Plaut & Shallice, 1993, Cogn. Neuropsych.).  The functional specialization in
the network that gives rise to the double dissociation is not transparently
related to the network's structure, as modular theories assume.  Furthermore, a
consideration of the distribution of effects across quantitatively equivalent
individual lesions in the network raises specific concerns about the
interpretation of single-case studies.  The findings underscore the necessity
of relating neuropsychological data to cognitive theories in the context of
specific computational assumptions about how the cognitive system operates
normally and after damage.

ftp-host: 	hydra.psy.cmu.edu [128.2.248.152]
ftp-file:	pub/plaut/papers/plaut.modularity.JCEN.ps.Z

[31 pages; 0.48Mb uncompressed]

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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."
Pittsburgh, PA  15213-3890	345H Baker Hall			--Voltaire
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=