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%2. Maak een onderzoeksvoorstel voor je Bachelorprojekt

%Hou hierover op 3 maart een korte presentatie (10 a 15 min.)

%Inleveren: onderzoeksvoorstel (4 a 5 pag),  incl. literatuuroverzicht (2 a 3 pag.), vraagstelling, motivatie, verwachte resultaat, tijdsplanning

\begin{document}
\section{Simulating Language Games of the Two Word Stage}
{\em Bachelor project proposal, Andreas van Cranenburgh (0440949), March 2009}

\subsection{Introduction}
General linguistics has been dominated by Chomskian generative linguistics for
several decades. The focus is on rules and their creativity, viz. systematicity
and productivity. The central dogma is that an in-born, Universal Grammar is
necessary to adequately explain these phenomena. It holds on to the continuity
assumption, which states that language as used and understood by children is
qualitatively equal to that of adults (Tomasello 2003).

However, from a developmental psychology angle, several empirical findings
(Tomasello 2000, 2003) shed doubt on whether this approach is applicable to language
acquisition by children. It rather appears that language learning is
bootstrapped in a haphazard fashion, learning constructions here and there,
which can only later be synthesized to form a coherent grammar.

Rather than trying to resolve this age-old debate between rationalism and
empiricism along theoretical lines, it might be fruitful to try to model the
behavior of early language users, and demonstrate in this way that a universal
grammar is in fact not necessary to explain the phenomena observed. This strategy
echoes a suggestion made by Turing (1950):

\begin{quote}
``Instead of trying to produce a programme to simulate the adult mind, why not
rather try to produce one which simulates the child's? [...] Presumably the
child-brain is something like a note-book as one buys it from the stationers.
Rather little mechanism, and lots of blank sheets.''
\end{quote}

\subsection{Previous work}
One of the foremost proponents of the developmental take on language acqusition is
Tomasello (2003). He argues that linguistic abilities are acquired gradually, in
an incremental fashion. Linguistic forms are memorized in conjunction with their
communicative functions or meanings. These constructions are then generalized so
that language use becomes ever more expressive and productive. Aspects which
distinguish this approach from that of generative linguistics is the rejection
of the autonomoy of syntax and the consequential focus on semantic and
pragmatic influences on learning. Aside from that the idiomatic dimension of
language presents problems for purely formal accounts of semantics and syntax,
so a certain informality should be embraced by models of language.

In a previous project three students and I (van Cranenburgh 2007) attempted to
model the two word stage of early child language. The model used a corpus of
utterances spoken to children, annotated with semantic representations of the
context. The aim was for this informal model to be able to generalize over the
sentences to discover the correct associations between words and their semantic
representations, and to be able to combine sentence fragments into novel
utterances. This model did not consider syntax and semantics separately, in the
style of construction grammar (Tomasello 2000, 2003). Although indeed correct
associations were found, and novel utterances could be recognized, most of the
former were incorrect, and most of the latter non-sensical (although in part
this was due to the first issue worsening the second). Here is an example of an
utterance as it was interpreted by our model:

\begin{verbatim}
1. "ball gone"  la score = 1
LINGUISTIC ABSTRACTION:
        WORDORDER: VAR:gone
        FRAME: action
                ID: action:move
                FRAME: object
                        ID: VAR
                        ABSTR: object:toy
\end{verbatim}

In this sentence the construction "X gone" was applied to "ball", because it
matched the condition of being a toy. The construction was apparently
previously encountered when a toy was being moved. 

The problem was that sentences were being learned as isolated fragments,
without any notion of discourse or pragmatics. Also, the semantic
representation did not fit well with all the words to be learned: it was good
at representing actions and objects, so prepositions and demonstratives and
other abstract words were not being learned. Instead of merely focusing on
semantically describing a situation, the learner should consider the total
communicative function of an utterance. The learning was implemented as
making associations between words and all possible parts of the semantic
representation, and counting how often these associations were made. This meant
that a lot of incorrect associations were made. Unfortunately the model did not
make use of pruning, so these incorrect associations were being retained.

Last year another project (Odolphi 2008) developed a formal grammar for the two
word stage, based on empirical work on child language (eg.\ van Kampen 2003).
This grammar does not make use of adult-like syntactic categories such as verb
and noun, but groups expressions as topics, comments and operators. Using this
grammar it is possible to produce plausible child utterances, because it turns
out that the almost all of the two word utterances follow the pattern of this
formal grammar.

%\subsection{Literature}


The work of van Kampen (eg. 2003) on children's' use of languages in the two
word stage indicates that their (proto-)grammar employs pragmatic operators and
content signs, instead of distinguishing all the syntactic categories present
in adult language. Verbs are not yet inflected, and determiners are absent.

Chang \& Gurevich (2004) demonstrate a computational model of Embodied
Construction Grammar that combines constructions to interpret new
constructions. Their semantic representation could serve as an inspiration for
how to improve the semantic representation. Also, the use of Minimum
Description Length learning provides a good way to prune the database of
learned constructions.

Steels (2004) describes his experiments with situated agents that employ
language games as a learning strategy. An example of a language game is the
description game: one agent describes an event that has just happened, and the
other responds by agreeing if the description matches its own experience.  

Van Kampen \& Scha (2007) discuss the modeling of early syntax acquisition using the Data Oriented Parsing framework. This means that all input is stored in
memory, and made available for recombination in the recognition of novel
utterances.

\subsection{Research question}
Can an examplar-based model of language acquisition account for the discrepancy
between language comprehension and production of children in the two word
stage? Can this model facilitate the simulation of simple language games
of parent and child?

These questions will be addressed by attempting to implement a simple model
of linguistic comprehension and production using an exmplar-based model of language.

\subsection{The model}
To answer this research question, a model will be devised. The model will start
with a collection of concepts and interpreted constructions. Concepts are
grouped as referents and predicates. Constructions are multi-word utterances
with a (possibly partial) interpretation of their meaning. 
Allow user of program to act as parent by specifying a
situation with an action and attention focusing, and making an utterance. Then
the program produces a child reaction, possibly using the mentioned two word
grammar. Eg. ``throw the ball'' and child reacts by acknowledging or refusing,
or by picking up the ball. The focus of the model will be to model interactions, not
the understanding and production of single utterances.

The model will make use of a database of examplars, storing all linguistic
input and associated situations. The discrepancy of speech comprehension and
production abilities can be simulated by employing differing algorithms
for comprehension and production. Comprehension should attempt to find the
meaning of an utterance by combining any possibly relevant examplars together.
Production can tuned to proceed conservatively.  Responses will be generated
using a very limited form of imitative creativity, perhaps informed by the
grammar of two word stage.  This discrepancy makes sense because the child
might lose the attention of its parent by saying incomprehensible or irrelevant
things, and on the other hand it is clear that before starting to speak
children have been listening to language for some time. Language has been
trickling in, but constructions that can be reproduced presumably need a
certain critical mass. 

An idea for indexing the examplars is to use perceptual hashes. These are like
normal hashes in that they compress the input with a high loss of information,
but different in that similar inputs yield similar hashes, so that there is an
effective way to compare the similarity of exemplars.

The last part will be to evaluate the model. Simple ideas are to judge whether
the model performs better than parrot behavior, or better than through simple
conditioning.  A more elaborate way could involve a kind of Turing Test:
presenting real and simulated parent-child dialogues to people and establishing
the recognition rate.

\subsection{Plan}

Breakdown of work to be done (12 weeks, the last 4 of which will be full time):
 
\begin{itemize}
\item 2 weeks: A corpus collected from selected fragments of available corpora (eg., CHILDES)
\item 2 week: Devise frame-based semantics formalism, and define speech act operators / language games
\item 3 weeks: Annotate the corpus using this formalism
\item 4 weeks: Implement analyses of adult utterances, implement response generation
\item 1 week: Evaluate cognitive plausibility of these responses.
\end{itemize}

%1. formuleer de huidige versie van de onderzoeksvraag

%2. maak een lijst van de meest relevante papers voor onderzoeksvraag (ca. 3 tot 12 papers)

%3. maak de referenties voor in het verslag

%4. maak een korte samenvatting van wat in het artikel van belang is

%5. maak een lijst van de belangrijkste ideeen en resultaten; formuleer elk item in het kort (ca. 1 alinea)

%6. maak een opzet in punten voor de tekst van het literatuuroverzicht en de "state of the art" van je onderzoeksvraag

\newpage
\subsection{References}
\begin{description}
\item[Chang, Nancy \& Gurevich, Olya] (2004) ``Context-Driven Construction Learning." Proceedings of the 26th Annual Meeting of the Cognitive Science Society. Chicago.

\item[van Cranenburgh,] {\bf Andreas, Arjan Nusselder, Nadya Peek \& Carsten van
Weelden} (2007): Towards a Computational Model for Early Language Acquisition,
2nd year bachelor of AI project. \\
\url{https://unstable.nl/andreas/ai/2p/laac/verslag.pdf}

\item[Tomasello, Michael] (2000) ``The item-based nature of children's earl syntactic development,'' Trends in Cognitive Science, Vol.\ 4, No.\ 4 (April 2000), pp.\ 156-163

\item[Tomasello, Michael] (2003), ``Constructing a Language. A Usage-Based Theory of Language Acquisition,'' Cambridge MA: Harvard University Press.

\item[van Kampen, Jacqueline] (2003) ``The learnability of Syntactic Categories," Proceedings of GALA.

\item[van Kampen, Jacqueline \& Scha, Remko] (2007): ``Modelling the Steps of Early Syntax Acquisition,'' Proceedings of the Workshop Examplar-Based Models of Language, Dublin.

\item[Steels, Luc] (2004): ``Constructivist Development of Grounded Construction Grammars," Proceedings of the 42nd Annual Meeting of the ACL, Barcelona.

\item[Odolphi, Ernst] (2008): ``Formal Grammars for Early Child Language,'' BSc.\ thesis, Artificial Intelligence, University of Amsterdam.

\item[Turing, Alan] (1950): ``Computing Machinery and Intelligence,'' Mind LIX, no. 2236 (Oct. 1950): 433-60

\end{description}

\end{document}
