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In S. Garrod & M. Pickering (Eds.), Language processing (pp. 233-279). Hove, U.K.: Psychology Press.
Connectionism and Natural Language Processing
Nick Chater & Morten H. Christiansen
Introduction
Many of the chapters of this book are concerned with topics in
language processing. This chapter is concerned, by contrast, with a
particular method, connectionist computational modelling, which has
been applied to a wide range of topics. It is, furthermore, a
controversial method: some have argued that natural language
processing from phonology to semantics can be understood in
connectionist terms; others have argued that no aspects of
natural language can be captured by connectionist methods. And the
controversy is particularly heated because of the revisionist
claims of some connectionists: for many, connectionism is not just an
additional method for studying language processing, but it offers an
alternative to traditional theories, which describe language and
language processing in symbolic terms. Indeed, Rumelhart &
McClelland (1987: p. 196) suggest ``that implicit knowledge of
language may be stored among simple processing units organized into
networks. While the behaviour of such networks may be describable (at
least approximately) as conforming to some system of rules, we suggest
that an account of the fine structure of the phenomena of language and
language acquisition can best be formulated in models that make
reference to the characteristics of the underlying networks.'' We
shall see that the degree to which connectionism supplants, rather
than complements, existing approaches to language is itself a matter
of debate. Finally, the controversy over connectionist approaches to
language is an important test case for the validity of connectionist
methods in other areas of psychology.
In the next section, Background we describe the historical and
intellectual roots of connectionism, then introduce the elements of
modern connectionism, how it has been applied to natural language
processing, and outline some of the theoretical claims that have been
made for and against it. We then consider four central topics in
connectionist research on language processing: Word naming and
visual word recognition, Lexical processing during speech,
Morphological processing and Syntax. These illustrate
the range of connectionist research on language, give an opportunity
to assess its strengths and weaknesses across this range, and allows
the general debate concerning the validity of connectionist methods to
be illustrated in specific contexts. We would argue that debates in
each of these areas, while interrelated, should each be considered on
their own merits: it may be that connectionist approaches are valuable
in modelling some aspects of language processing, but not in others.
Finally, in the Conclusions we sum up and consider the
prospects for future connectionist research, and its relation to other
approaches to understanding language processing and language
structure.
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