OT learning and the development of coreference Reinhard Blutner University of Amsterdam Anton Benz Syddansk University Kolding 2005

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

12/7/2005Groningen3 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).

12/7/2005Groningen4 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.

12/7/2005Groningen5 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  Thus how do we reconcile children’s poor performance on comprehension tasks with their near-perfect production data?

12/7/2005Groningen6 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.

12/7/2005Groningen7 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)

12/7/2005Groningen9 Optimality Theory as a Framework Contraint-Hierarchy: C1 >> C2 >> C3 Evaluator Output Input Generator Candidates

12/7/2005Groningen10 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)

12/7/2005Groningen11 Constraints (slidely modifying Burzio 1998)  PRINCIPLE A: A reflexive must be bound locally  REFERENTIAL ECONOMY: Avoid R-expressions >> Avoid pronouns >> Avoid reflexives pro self disjconj pro self disjconj PRINCIPLE A REFERENTIAL ECONOMY

12/7/2005Groningen12 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. pro self disjconj pro self disj conj

12/7/2005Groningen13 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 disjconj pro self disjconj strong bidirection weak bidirection

12/7/2005Groningen14 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. pro self disjconj pro self disjconj strong bidirection weak bidirection

12/7/2005Groningen15 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.

12/7/2005Groningen16 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)

12/7/2005Groningen17 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.

12/7/2005Groningen18 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

12/7/2005Groningen20 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) = 0elsewhere  EU(S,H) =  P(m i ) U(S,H,m i )

12/7/2005Groningen21 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)

12/7/2005Groningen22 Forms of Learning Agent x Teacher Sx Hx Agent x Teacher Sx Hx Agent x Sx Hx Agent y Sx Hx supervised learning unsupervised learning cultural learning

12/7/2005Groningen23 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 pro self disjconj pro self disjconj Bias Constraints Markedness Constraints A B

12/7/2005Groningen24 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.

12/7/2005Groningen25 The Initial Step Teacher –*H –*S pro self disjconj pro self disjconj A B Learner –S –H pro self disjconj A pro self disjconj B L0L0 L 1: A-first (ambiguous pro) L 1: B-first (ambiguous self) A-first B-first Initial State

12/7/2005Groningen26 The Final Step Teacher –*H –*S pro self disjconj pro self disjconj A B pro self disjconj A L0L0 L 1: A-first L2L2 pro self disjconj A B

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 implicatures some elephants have a trunk