ot learning and the development of coreference reinhard blutner university of amsterdam anton benz...

OT learning and the development of coreference

Reinhard BlutnerUniversity of AmsterdamAnton BenzSyddansk University Kolding2005

1 Introduction

In an important recent article Hendriks and Spenader (2004) give a new interpretation of children‘s delay of the comprehension of pronouns. We discuss the validity of this interpretation and present an alternative account in terms of evolutionary learning

12/7/2005 Groningen 3

The Pronoun Interpretation Problem

(1) Bert saw himself(2) Bert saw him

Children correctly interpret reflexives like adults from the age of 3;0 but they continue to perform poorly on the interpretation of pronouns even up to the age of 6;6

Sentences like (1) are correctly understood from a young age (95% of the time according to some studies), but the him in (2) is misinterpreted as coreferring with the subject about half the time.

E.g. Jakubowicz (1984); Koster and Koster (1986); Chien and Wexler (1990); McDaniel, Smith Cairns and Hsu (1990); McDaniel and Maxfield (1992); McKee (1992); Grimshaw and Rosen (1990).


Children‘s Production of Pronouns and Reflexives

(3) I hit myself.(4) John hit me(5) * I hit me. Bloom et al. (1994): Even in the youngest age

groups investigated (ranging from 2;3 or 2;4 to 3;10), the children consistently used the pronoun me to express a disjoint meaning (99.8% correct), while they used the reflexive myself to express a coreferential interpretation (93.5% correct).

Conclusion: very young children have competence in binding principles.


The problem

Usually, comprehension of a given form precedes production of this form – Bates, Dale and Thal 1995; Benedict 1979;

Clark 1993; Fraser, Bellugi and Brown 1963; Goldin-Meadow, Seligman and Gelman 1976; Layton and Stick 1979.

Thus how do we reconcile children’s poor performance on comprehension tasks with their near-perfect production data?


Previous accounts Reject the comprehension data (Bloom et a. 1994)

– the tasks used in the comprehension experiments did not adequately test children’s grammatical competence

Dissociation between a comprehension grammar and a production grammar.– requires some ad hoc stipulations

Revise the binding principles, making a distinction between coindexation and coreference (Chien and Wexler 1990; Grodzinsky and Reinhart 1993). – This is based on the observation that children seem to

correctly interpret pronouns in the scope of quantified noun phrases.


Outline

Hendriks & Spenader‘s account (accepting the data and the original binding theory)

The evolutionary approach The evolution of binding (Mattausch) General Discussion Conclusions

1 Hendriks & Spenader‘s account

“Our account, formulated in the framework of Optimality Theory handles the comprehension data as well as the production data by arguing that children acquire the ability to reason about alternatives available to other conversation participants relatively late. It is this type of bidirectional reasoning, we argue, that is necessary for correctly interpreting pronouns.” (H&S 2004)


Optimality Theory as a Framework

Contraint-Hierarchy:C1 >> C2 >> C3 Evaluator

Output

Input

Generator

1 2 3 4 5Candidates


Bidirectional OT

Consider two directions of optimization (Hearer-oriented, Speaker-oriented)

Use the same set of constraints and the same ranking for both perspectives

Hence, the evaluator evaluates pairs of representations (e.g. form-meaning pairs)


Constraints(slidely modifying Burzio 1998)

PRINCIPLE A: A reflexive must be bound locally

REFERENTIAL ECONOMY: Avoid R-expressions >> Avoid pronouns >> Avoid reflexives

proself

disj

conj

proself

disj

conjPRINCIPLE A REFERENTIAL ECONOMY


Assuming a Ranking

PRINCIPLE A >> REFERENTIAL ECONOMY

Hearer‘s perspective: one optimal interpretation for self but two optimal interpretations for pro.

Speaker‘s perspective: correct unique form for each interpretation.

proself

disj

conj

pro

self

disj

conj


Strong and Weak Bidirection 1

Strong bidirection associates best form with best meaning (the figure is using alternative constraints!)

Weak bidirection is a recursive bidirection that (step-by-step) restricts the set of available alternatives. pro

self

disj

conj

proself

disj

conjstrong bidirection weak bidirection


Strong and Weak Bidirection 2

We use the constraints taken by Hendriks & Spenader

Whereas weak bidirection sometimes yields more solutions than strong bidirection, in the present case they give the same result.

proself

disj

conj

proself

disj

conjstrong bidirection weak bidirection


Delayed (Weak) Bidirection The proposal is that children begin with

unidirectional optimization, and only later acquire the ability to optimize bidirectionally.

A child must, when hearing a pronoun, reason about what other non-expressed forms the speaker could have used, compare the interpretation associated with the pronoun and realize that a coreferential meaning is better expressed with a reflexive. Then, by a process of elimination, the child must realize the pronoun should be interpreted as disjoint.

Optimizing bidirectionally inherently involves reasoning about alternatives not present in the current situation, which may be a skill acquired very late, thus explaining the lag in acquisition.


Advantages The authors are able to derive Principle B

effects from Principle A alone, through bidirectional optimization.

The analysis clearly distinguishes the task of a speaker from the task of a hearer. As a result the analysis is able to model different results for production and comprehension.

Besides the stipulation of the constraints and their ranking no other stipulations are required

The approach nicely combines a pragmatic explanation with a processing account (lack of processing resourses)


Disadvantages The constraints are partly stipulated - no constraint

grounding For the solution of the optimization task strong

bidirection is enough. There is no big difference of processing load for unidirectional optimization and strong bidirection (Kuhn 2004)

Theory of Mind (Perner, Leekam and Wimmer 1987) requires awareness of other conversation participant’s choices. Hence, theory of mind is based on controlled rather than automatic processing. However, the effects of pronoun processing are automatic rather than controlled. There is no explicit hint for mind reading capacities in such tasks

Beaver’s and Zeevat’s arguments against strong bidirection as an online mechanism.


A Reinterpretation of Hendriks & Spenader‘s account

We propose a reinterpretation based on the idea that the ranked system of constraints is changing during learning

Rather than stipulating a change from unidirectional to bidirectional processing we account for the effects of (weak) bidirection by only changing the constraint ranking

Bidirectionally otimal pairs in the original system come out as unidirectionally optimal pairs in the developed system.

Our system explains why principle B (taken as an OT constraint) is delayed – in a literal sense.

Our modell can be extended to the case of language change by cultural evolution.

OT learning theory


Hearer‘s and Spreaker‘s strategies

Speaker‘s strategy: given the possible utterance meanings m, the OT system specifies a function S(m)

Hearer‘s strategy: given the possible language forms F, the OT system specifies a function H(F)

1 if m = H(S(m)) U(S,H,m) =

0 elsewhere EU(S,H) = P(mi) U(S,H,mi)


Learning as utility optimization

Learning consists in improving the value of expected utility.

In OT-learning theories the ranking of a given system of constraints is (stepwise) changed

Learning leads to a stable outcome if the relevant EU(s) reach its maximum value

Forms of learning can be classified according to the role (Speaker/Hearer) that is taken by the agent (and the role which is possibly taken by an external agent)


Forms of Learning

Agentx

Teacher

S x

H x

Agentx

Teacher

S x

H x

Agentx

S x

H x

Agentx

Agenty

S x

H x

supervised learning

unsupervised learning

cultural learning


Constraints (selection) Bias Constraints

– PRINCIPLE A: A reflexive must be bound locally– PRINCIPLE B: A pronominal is free (in its

governing cat)

Markedness Constraints– DISJOINT REFERENCE: disj > conj– EXPRESSIVE ECONOMY: pro > self

proself

disj

conj

proself

disj

conjBias Constraints Markedness

Constraints

AB


Assumptions for describing stages of learning

1. There is a teacher who is a competent speaker/hearer of the language. He takes both roles.

2. The initial state of the learner (initial ranking of the constraints): markedness constraints dominate bias constraints.

3. The reranking of a bias constraints is the crucial element for defining an developmental step. In each step only one reranking of a bias constraint is allowed (but many rerankings of other constraints)

4. If there are different possibilities for reranking the constraints, the ranking with the highest EUs wins.


The Initial StepTeacher– *H– *S

proself

disj

conj

proself

disj conj

AB

Learner– S– H

proself

disj

conj

A

proself

disj

conj

B

L0

L1: A-first

(ambiguous pro)

L1: B-first

(ambiguous self)0.1 0.2 0.3 0.4 0.5Prob for Conj

0.6

0.7

0.8

0.9

1

EU

A-first

B-first

Initial State


The Final Step

Teacher– *H– *S

proself

disj

conjpro

selfdisj co

nj

AB

proself

disj

conj

A

L0

L1: A-

first

L2

proself

disj conj

AB

Conclusions Languages are evolving via cultural rather

than biological transmission on a historical rather than genetic timescale. This explains the cultural evolution of binding principles (Mattausch)The idea is an instance of the ‚universal Darwinist‘ claim (Dawkins 1983, Dennett 1995) that the methodology of evolutionary theory is applicable whenever any dynamical system exhibits (random) variation, selection amongs variants, and thus differential inheritance

In language acquisition a similar learning theory can applied but this time with two players only: child + adult (fixed strategy)

The explanation of the development of binding behavior is memory-based, not processing-based

Generalizations?? – Acquisition of scalar implicaturessome elephants have a trunk

ot learning and the development of coreference reinhard blutner university of amsterdam anton benz...

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