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Review of  Dynamical Grammar


Reviewer: Smaranda Muresan
Book Title: Dynamical Grammar
Book Author: Peter W. Culicover Andrzej Nowak
Publisher: Oxford University Press
Linguistic Field(s): Linguistic Theories
Psycholinguistics
Syntax
Cognitive Science
Book Announcement: 15.2358

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Review:
Date: Sun, 22 Aug 2004 20:41:13 -0400 (EDT)
From: Smaranda Muresan <smara@cs.columbia.edu>
Subject: Dynamical Grammar: Minimalism, acquisition, and change

AUTHOR: Culicover, Peter W.; Nowak, Andrzej
TITLE: Dynamical Grammar
SUBTITLE: Minimalism, acquisition, and change
PUBLISHER: Oxford University Press
YEAR: 2003

Smaranda Muresan, Natural Language Processing Group, Department of
Computer Science, Columbia University

OVERVIEW
''Dynamical Grammar'' is the second volume of a two-volume work on
''Foundation of Syntax'', offering a new perspective, minimalist and
dynamical, on language acquisition and language change. While the main
goal of the first volume (Culicover, 1999) was to investigate the
properties of language as bounding conditions on the learning
mechanism, the current book explores the actual architecture of the
learner and the linguistic theory most compatible with the facts of
language.

The book is addressed mainly to linguists, psycholinguists and
cognitive scientists. However, computational linguists interested in
language learning can greatly benefit from the material presented in
this book.

SYNOPSIS
The book comprises three parts: Foundations (Chapter 1-2),
Simulations (Chapter 3-6) and Grammar (Chapter 7).

Part I presents a minimalist, dynamical approach to language
acquisition (Chapter 1) and discusses how the link between linguistic
theory and language acquisition can be rethought in this dynamical
view (Chapter 2).

In Chapter 1, ''The Dynamical Perspective'', the authors argue in
favor of a minimalist, dynamical approach to language acquisition,
language evolution and language processing. It is minimalist since it
looks for the minimal formal machinery and prior knowledge that the
learner has access to in order to acquire language. It is dynamical
because it considers the architecture of language faculty to be a
dynamical system. The authors discuss Concrete Minimalism (Culicover
1999) as a linguistic theory tightly linked to the dynamical
approach. They present in general terms how language acquisition can
be modeled by an adaptive, dynamical system: forms and meanings are
represented as trajectories in the linguistic space; trajectories are
acquired individually; similar trajectories are grouped into flows,
and generalizations emerge from these groupings.

Chapter 2 challenges the traditional view on the link between language
acquisition and linguistic theory in both ''how'' language is acquired
and ''what'' is actually acquired. ''The central thesis of this
chapter is that current formal grammatical descriptions of adult
language do not offer the proper vocabulary for describing the course
of language acquisition'' (p. 23). The authors presents a critical
analysis of Principles and Parameters Theory (PPT), considering
several issues regarding parameters, parsing and triggers, mistakes,
idioms and irregularities. They argue against an innate skeletal
grammar with default values of all the parameters, as PPT assumes, and
propose that ''the learner does have something structured that it
draws upon in establishing correspondences between sounds and meaning,
namely, the infinite inventory of meanings, the capacity to generalize
and knowledge of what constitutes warranted generalization, and the
capacity to extract formal regularities from the language that it is
exposed to'' (p. 42) .

Part II presents several computer simulations for testing various
hypotheses about language acquisition (Chapter 3, 4 and 5) and
language change (Chapter 6).

The simulations in Chapter 3, 4 and 5 search for the minimal
mechanisms the learner needs in order to acquire language. The
conclusion is that neither distributional, nor grammatical approaches
can alone justify language acquisition, that each of them plays a
role. In all simulations, artificial data sets, as well as transcripts
from the CHILDES database (MacWhinney 1995) were used. The mechanisms
contained in the system were systematically varied in order to
explore what features of the grammar the learner acquires given
different assumptions.

Chapter 3, which focuses on the distributional approach to language
learning, concludes that the ability to statistically acquire
regularities in language is not sufficient for grammar learning. The
authors present their system, Aqui, which is a dynamical system in
which there is no meaning associated with words or sentences. The
authors also analyze the amount and type of knowledge in the input
data itself. They present Clagen, a genetic algorithm system that
identifies optimal clustering in a corpus, based on distributional
information. Quantitative and qualitative analyses show that the
clustering method discovers mainly semantic co-occurrence restrictions
in the data, but no syntactic structure. The results of Aqui and Clagen
suggest that in order to learn grammar, there is a need for additional
information, which the authors argue to be the meaning.

Chapter 4 and 5 explore whether access to meaning is not only
necessary, but also sufficient for grammar learning, given that in the
system there exists mechanisms for finding associations between
meaning and form.

Chapter 4 presents CAMiLLe (Conservative Attentive Minimalist Language
Learner), a system which implements the theory of Concrete Minimalism
in the form of a dynamical system. Chapter 5 presents experiments done
with this system. As nicely stated in Part III, the key properties of
CAMiLLe are: ''i) the learner is presented minimally with strings and
their associated conceptual structures, ii) the learner is
Conservative in formulating hypotheses and in generalization, iii) the
learner is Attentive to detail, iv) the learner formulates a set
correlations that expresses the pairings of strings and their
conceptual structures'' (p. 241).

Chapter 4 starts with a presentation of CAMiLLe's properties derived
both from the theory of Concrete Minimalism and from computational
considerations (p. 103): e.g., access to meaning in the form of
Jackendoff's Conceptual Structures; capacity to form categories, while
not having the information of what these categories are; access to the
notions of ''phrase'' and ''head of a phrase'', a.s.o.

CAMiLLe has two representation systems: one for meaning and one for
sentences, corresponding to classical semantics and syntax. The
authors present the dynamical view of these systems, and explain what
language learning means in this approach: finding couplings between
trajectories of the syntactic and the semantic system. This is equivalent
to finding correspondence rules between form and
meaning. Generalization is seen as a self-organization of the language
space based on repeated experience.

Parsing is what permits CAMiLLe to identify syntactic structure. The
sentence is not just a string of words, but it has a structure
associated with it, which emerges from contracting the strings of
words to their heads. The authors present the characteristics of
parsing, and briefly discuss the treatment of embedded clauses,
representation of phrase structure, transformations, emphasizing that
CAMiLLe is attentive to linear order. How the system will deal with
null arguments, transformations, word-ordering will be presented in
Chapter 5.

Chapter 5 discusses some experiments with CAMiLLe, showing initial
results and pointing to future research. The authors organize
the chapter into three main parts corresponding to
experiments regarding the lexicon, the phrase structure, and the word order.

For the lexicon, experiments are done for nouns, compound nouns, verbs
and verbal inflection and synonymy/ambiguity. Authors point out in
the Section ''Dummy Semantics'' that a realistic simulation would need
larger data sets, which are hard to build. They present as an
alternative the use of dummy semantics. For lexicon, they present
experiments with flat dummy semantics, but they avow that this is
not sufficient to learn structure and hint in a footnote that a
different kind of dummy semantics will be needed: bracketed
strings.

The experiments regarding structure look at the discovery of DP
structure (determiners, modifiers, argument structure), showing
several positive results, as well as problematic phenomena where
further experimentation is needed. The authors discuss in these cases
the possible reasons of failure: not enough information, the task is
difficult, the learner needs to be enhanced.

Regarding word order, they explore word order correlates of
argument structure, scrambling, inversion, wh-movement and null
arguments. An interesting point is the reinforcement of Elman's
discovery (Elman 1993) that too much and complex information at the
outset may confuse the learner, leading him to spurious
generalizations.

The last two sections of this chapter,''Extending CAMiLLe'' and
''Preconditions for language acquisition by CAMiLLe'', are a
remarkable discussion of the overall results of the simulations,
showing the characteristics of CAMiLLe, its performances and future
directions.

Chapter 6 reports on simulations of language change and language
evolution from the dynamical perspective. This chapter elaborates on
the authors' previous papers, (Culicover et al. 2003), (Culicover and
Nowak 2003), and present them within a unified framework. The authors
argue that the same dynamical system architecture and
self-organization mechanism are suitable for both language acquisition
and language change. Section 6.2 presents a computer simulation of
language change (extending the material from (Culicover et al. 2003)),
while Section 3 presents several extensions to the model (including
bias, and variations across lexical populations) and discusses the
computational complexity issue (a summary of the discussion in
(Culicover and Nowak, 2003)). They argue that ''the major grammatical
constraint that guides the direction of change is the computational
complexity of the sound-meaning correspondence'' (p. 22).

Part III (Chapter 7) presents ''Concrete Minimalism'' as a link
between syntactic theory and the dynamical perspective on language
acquisition and language change. This concluding chapter
crowns the monumental work on two volumes about Foundations of
Syntax. The chapter has two parts.

Part one (Section 7.1) presents the major formal design features of
language and how they can be represented in a dynamical system that
conforms with Concrete Minimalism. This part is a very detailed
presentation of the dynamical system, giving a more formal definition
(p. 246) and showing in greater detail how language, and in particular
syntax can be represented as a dynamical system (lexical categories,
phrasal categories (endocentric, exocentric, movement and recursion).

Part two (Section 7.2-7.8) shows how Concrete Minimalism allows for
''descriptively adequate syntactic descriptions, and following Occam's
Razor, is to be preferred to other syntactic theories that invoke more
abstract structure'' (p. 22). In this approach, linear order is
considered a primitive in the grammar. The phenomena covered are some
of the most prominent ones studied in the context of PPT:
head-complement order, V raising to I, V2 and Inversion, Null
arguments, Wh-movement and Scrambling. The authors present an analytic
discussion of both traditional approaches and the Concrete Minimalism
account of these phenomena. The main conclusion is that Concrete
Minimalism coupled with a theory of markedness can explain these
phenomena and it should be preferred, as a simpler approach.

CRITICAL EVALUATION
''Dynamical Grammar'' can be recommended on several levels, being in
my opinion one of those revolutionary and fundamental books that have
an interdisciplinary impact, moving the research on language
acquisition and language change to a next level. The book
provides an excellent discussion of related work in linguistics,
cognitive science and computational linguistics.

The authors evaluate this work to be ''a model of qualitatively
understanding of how language acquisition may be represented as a
self-organization of a dynamical system''(p.189). However, I see two
dimensions, besides the unified framework, that the book can be
appreciated and evaluated upon: the linguistic theory (Concrete
Minimalism) and the learning theory (Dynamical Systems). I found
Chapter 7 to be a very powerful chapter that ties them together.

An aspect of Concrete Minimalism that might be found appealing by both
linguists and computational linguists is the tendency towards a
simpler syntax. In this view, the grammar explicitly states
correspondences between form and meaning. The simulations with
CAMiLLe, and the detailed presentation of its properties (p. 103 and
p. 190) give valuable insight on what might be the minimal information
a learner needs in order to acquire language. This book presents
consistent positive results that support the authors' general
approach. What I found also very useful, is the discussion of the
limitations of the current implementation and how future research can
address them: e.g., CAMiLLe does not currently generalize to basic
categories. The questions that arise are: would additional mechanisms
will be needed and would they be sufficient, or the learner would need
this information to start with. The authors argue for the first
solution and present a brief discussion. Another zone of further
research, as the authors themselves point to, resides in the
generalization mechanism (i.e., should the learner be conservative, or
it should allow overgeneralization, but then supply an error
correction mechanism).

Overall I found this book to be a thought provoking reading, rich in both
theoretical arguments and experimental validations. I foresee this work
to open several doors not only to work in linguistic theory and
cognitive science, but also to computational linguistics focusing on
grammar induction and language understanding. Moreover, this book is a
clear example of how valuable the interdisciplinary work is for
studying language acquisition and language change. In general, as
computer simulations become a bigger part of the approaches taken for
the study/experimentation of language acquisition and language
evolution theories (see also Briscoe (2002)), I think closer
collaborations between linguists, cognitive scientists on one hand, and
computational linguists on the other hand, can lead to further
developments.

REFERENCES
Briscoe, Ted (editor) (2002). ''Language Evolution through Language
Acquisition: Formal and Computational Models''. Cambridge University
Press, Cambridge, UK, 2002.

Culicover, Peter W. (1999). ''Syntactic Nuts: Hard Cases, Syntactic
Theory, and Language Acquisition''. Oxford University Press. 1999.
Volume One of Foundations of Syntax.

Culicover, Peter W. and Andrzej Nowak (2003). ''Markedness,
Antisymmetry and Complexity of Constructions''. In Pierre Pica and
Johann Rooryk, eds. Variation Yearbook. John Benjamins,
Amsterdam. 2003.

Culicover, Peter W., Andrzej Nowak, and Wojciech Borkowski (2003).
''Linguistic Theory, Explanation and the Dynamics of Grammar''. In
John Moore and Maria Kolinsky, eds. Explanation in Linguistic Theory,
CSLI Press, Stanford, CA. 2003.

Elman J. L. (1993). ''Learning and Development in Neural Networks: The
Importance of Starting Small''. Cognition, 48:71-99.

MacWhinney B. (1995). ''The CHILDES Project: Tools for Analyzing
Talk''. Hillsdale, NJ: Lawrence Erlbaum Associates, 1995.
 
ABOUT THE REVIEWER:
ABOUT THE REVIEWER
Smaranda Muresan is a PhD Candidate in the Natural Language Processing
Group, Department of Computer Science, Columbia University. Her
research interests are in the field of computational linguistics,
including grammar learning and natural language understanding. In her
PhD thesis, she proposes a relational learning framework for the
induction of grammars able to capture both aspects of syntax and
semantics. She uses a domain ontology during the learning process as a
grammar semantic constraint.

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