gundel & poesio - computational approaches to reference

July 2003 LSA Summer School 1

Gundel & Poesio - Computational Gundel & Poesio - Computational Approaches to ReferenceApproaches to Reference

Massimo Poesio (University of Essex)

Lecture 2:More on the Interpretation of Anaphora Psychological Evidence


A quick recap / clarification re: A quick recap / clarification re: interpreting referring expressionsinterpreting referring expressions

In FAMILIARITY-BASED theories such as ‘Vanilla DRT’, each type of referring expression assumed to EITHER always introduce a new discourse entity (INDEFINITES) or to always require an appropriate discourse entity to be found in context to provide the interpretation (DEFINITES)In this course we will mostly focus on nominals usually classified as DEFINITES, but we are NOT assuming familiarity as the defining feature of definiteness – we only take it to be an important property of many definitesNevertheless, we will mostly be concerned with methods to identify the `appropriate discourse entity in context’, if one is there – I.e., on FAMILIAR, ACTIVATED and IN-FOCUS entities

Except for definite descriptions (W3, L1)


Today’s lectureToday’s lecture

Discourse modelsConstraints and preferences in anaphora interpretationThe time course of anaphora interpretation(If time allows) Commonsense- and recency- based methods for pronominal interpretation


Interpreting referring expressionsInterpreting referring expressions

Interpreting (‘resolving’) a referring expressions involves at least three steps:1. Deciding whether it refers to a familiar discourse entity, or

whether it introduces a new discourse entity2. If it’s familiar, identifying its antecedent (possibly not

introduced by a nominal)3. Determining its meaning (identity of sense vs. identity of

reference)

(These three steps not necessarily taken in this order)


The Antecedents of Anaphoric The Antecedents of Anaphoric Expressions: Discourse Expressions: Discourse Comprehension and ContextComprehension and Context

Interpreting anaphoric expressions requires keeping track of antecedents available in context:

A man and a woman entered the room. The man sat down. (Anaphora)John got home. He was feeling very tired. (Anaphora)The ship came into the harbour. It docked. (Temporal order)

Context contains more than just objects which are mentioned:

John bought a new car. The engine needed tuning. (Clark, 1977)When Ross visited his Aunt Cecily, they spent the afternoon talking. Then, as arranged, Nadia arrived. Ross kissed his aunt good-bye, and set off with Nadia to the discotheque, where they danced the night away. (Hirst, 1981)

Massimo Poesio:

Use classic examples from Webber / Karttunen

Massimo Poesio:

Use classic examples from Webber / Karttunen


The Discourse Model as a separate The Discourse Model as a separate level of representationlevel of representation

Entities introduced in discourse model do not necessarily denote anything ‘in the real world’:

We don’t have a car, which is a shame, because we could really use ?it / one. If I had a DVD reader, I could use it to play movies on my notebook.

Arguments in linguistics and CL literature: Karttunen 1967, 1976; Webber, 1978; Kamp and Reyle, 1993.


Discourse Models in the Discourse Models in the Psychological Literature: A HistoryPsychological Literature: A History

Context as list of structural representationss-structures: many AI algorithms (e.g., Hobbs)d-structures (Miller; Fodor, Bever, and Garrett, 1974)

Propositional Representations (Kintsch and van Dijk, 1978; Clark and Sengul, 1979)

Context = list of propositions (possibly hierarchically structured)Motivations: Lesgold 1972, Ratcliff and McKoon 1978, Clark and Sengul’s experiments, among others

Bransford and Franks, 1971; Bransford, Barclay, and Franks, 1972; Barclay, 1973: mental models

Subjects perform additional inferences which seem to be based on their building a model of the situation

Johnson-Laird, 1983; van Dijk and Kintsch, 1983: Context = Mental models + linguistic representations

Massimo Poesio:

Best discussion of these issues: Fletcher 1994Need to look at Kintsch and van Dijk, as well?Check Stavroula’s referencesThis should become ‘varieties of discourse models’ without mentioning psych

Massimo Poesio:

Best discussion of these issues: Fletcher 1994Need to look at Kintsch and van Dijk, as well?Check Stavroula’s referencesThis should become ‘varieties of discourse models’ without mentioning psych


Background: Self-paced reading Background: Self-paced reading experimentsexperiments

Clark and Sengul 1979 are example of self-paced reading studyIn this type of studies, the subjects read text by pressing a button so that parts of the text are displayed on a computer screenThe computer measures the time between button pressesVariants:

Amount of text displayed: a whole sentence (as in Clark and Sengul’s experiment), a clause (e.g., Stevenson Crawley and Kleinman 1994, tomorrow), a single word Display can be cumulative, or each press can completely replace previous textEtc.


Context as an ordered list: Context as an ordered list: Clark and Sengul’s experimentsClark and Sengul’s experiments

Subjects read a context with three sentences, and a target sentence containing a reference to an entity mentioned in context sentence 1, 2 or 3 (pronoun or noun)Example:

The campers erected a shelter of lightweight plastic in the clearing. They piled a supply of dry wood next to a tree. The smell of coffee mingled with smoke from the campfire. TARGET2: The tree was an enormous redwood.

Results:

Significant effect of distance: F’=18.99, p < .001

Type of nominal

Context Sentence 1

Context Sentence 2

Context Sentence 3

Full NP 2174 2166 1802

Pronoun 2280 2133 1847

Mean 2227 2150 1825

Massimo Poesio:

Main point: antecedent much faster when in context 3 than in 2 or 1

In fact, this has more to do with local focus / global focus separation than propositional vs. situational (perhaps Lesgold 1972 would have been better!)

Massimo Poesio:

Main point: antecedent much faster when in context 3 than in 2 or 1

In fact, this has more to do with local focus / global focus separation than propositional vs. situational (perhaps Lesgold 1972 would have been better!)


The problem with ‘purely structural’ The problem with ‘purely structural’ views of contextviews of context

The discourse model must clearly contain SOME syntactic information:

At least agreement informationJane blamed Bill because he spilt the coffee

‘Parallelism’ effects suggest that some structural information is available, too

But clearly anaphora resolution cannot be simply a matter of copying structural information:

Bach-Peters sentencesThe pilot that shot at it hit the Mig that chased him.

Webber:John gave Mary five dollars. It was more than he gave Sue.John gave Mary five dollars. One of them was counterfeit.


Bransford, Barclay, and Franks, 1972Bransford, Barclay, and Franks, 1972

CONTEXT: Three turtles rested on a floating log and a fish swam beneath them.

(a): Three turtles rested beside a floating log, and a fish swam beneath it.

(b): Three turtles rested on a floating log and a fish swam beneath it.

Result: correctly rejected (a) but accepted (b)


Mental modelsMental models

These experiments suggested that contexts are not simply lists of propositions, but that these propositions are somehow ‘merged’ to create `world-like’ representations Johnson-Laird, 1983: While processing, humans construct representations of worlds/ situations related (identical with?) those built from perceptionReasoning is reasoning with these representations

Massimo Poesio:

Some of these inferences could be performed with propositional

representations, as well (in fact, this might be what Haviland claimed?).

Indeed, Frazier claims just that.

Massimo Poesio:

Some of these inferences could be performed with propositional

representations, as well (in fact, this might be what Haviland claimed?).

Indeed, Frazier claims just that.


Some preliminary considerationsSome preliminary considerations

Some of the discussion concerning the supposed dichotomy between ‘propositional representations’ and `mental models’ appears to reflect a misunderstanding about reasoning:No reason in principle why a human subject, given a propositional representation of the facts about turtles & logs, & knowledge about spatial relationships, shouldn’t be able to (defeasibly) make additional inferences & conclude that the fish is under the log. This fact would ALSO be represented in propositional format In fact, in most modern logic we have an equivalence between ‘syntactic’ inference and ‘semantic’ inferenceIn order to argue for a ‘situational’ representation, one has to argue that the inferences that take place are very idiosyncratic (difficult to prove)


A formal discourse model: Discourse A formal discourse model: Discourse Representation Theory (Kamp and Reyle, Representation Theory (Kamp and Reyle, 1993)1993)

M W Y Z E

man(M)

woman(W)

room(Z)

Y = M+W

E: entered(Y,Z)

man(X)

S: sat-down(X)

X = M

X S

A man and a woman entered the room. The man sat down.

Massimo Poesio:

Point here: both the ‘propositional’ and the ‘situational’ view of context are merged in DRT& similar formalisms

Massimo Poesio:

Point here: both the ‘propositional’ and the ‘situational’ view of context are merged in DRT& similar formalisms


DRT vs Mental Models TheoryDRT vs Mental Models Theory

DRT can be viewed as a formalization of mental models Advantages:

Propositional / mental model distinction disappearsMore precise theories of the meaning of anaphoric expressions and of semantic composition

Differences:Inference in mental models is not classical

But: unclear whether mental models really have ‘spatial’ structure

Massimo Poesio:

Check Fletcher 1994 though – he does seem to believe that there is evidence for spatial arrangement!

(E.g., Mani and Johnson-Laird)

Massimo Poesio:

Check Fletcher 1994 though – he does seem to believe that there is evidence for spatial arrangement!

(E.g., Mani and Johnson-Laird)


Semantics of anaphoric expressionsSemantics of anaphoric expressions

Psychological work often unclear about the precise interpretation of certain anaphoric expressions; even more so about how this interpretation is compositionally derived.Some of them (eg., Garnham; Sanford) now rely on ideas from formal semantics Simplifying assumptions: ignore sense anaphora; uniform treatment of bound and referring anaphora a la DRT

Massimo Poesio:

Another advantage of linguistic representations of discourse models

Massimo Poesio:

Another advantage of linguistic representations of discourse models


Anaphoric expressions in DRTAnaphoric expressions in DRT

M W Y Z E

man(M)

woman(W)

room(Z)

Y = M+W

E: entered(Y,Z)

man(X)

S: sat-down(X)

X = ?

X S

Massimo Poesio:

Although formal semantics very explicit about meaning of AE after resolution, not always very clear about their lexical meaning.

Here, simplifying assumption.

Massimo Poesio:

Although formal semantics very explicit about meaning of AE after resolution, not always very clear about their lexical meaning.

Here, simplifying assumption.


If we really keep all the antecedents If we really keep all the antecedents in the discourse model … in the discourse model …

The Hodja was walking home when a man came up behind him and gave him a thump on the head. When the Hodja turned round, the man began to apologize, saying that he had taken him for a friend of his. The Hodja, however, was very angry at this assault upon his dignity, and dragged the man off to court. It happened, however, that his assailant was a close friend of the cadi [magistrate], and after listening to the two parties in the dispute, the cadi said to his friend: “You are in the wrong. You shall pay the Hodja a farthing damages.”

His friend said that he had not that amount of money on him, and went off, saying he would get it. Hodja waited and waited, and still the man did not return. When an hour had passed, the Hodja got up and gave the cadi a mighty thump on the back of his head. “I can wait no longer”, he said. “When he comes, the farthing is yours.”

(From Downing, Tales of the Hodja, 1964 (reported in Hirst (1981)))

Massimo Poesio:

First step: find the antecedents.

Discourse model our search space.

Massimo Poesio:

First step: find the antecedents.

Discourse model our search space.


Yet, all (or at least a ‘currently Yet, all (or at least a ‘currently salient subset’) are accessed in salient subset’) are accessed in parallel parallel

Corbett and Chang, 1983: all antecedents of a pronoun are accessed

Tanenhaus et al, 1995: all antecedents of a definite description referring to a visual situation are accessedAs a result, the more ambiguous, the slower (Fredriksen, 1981; Garnham, 1989)Same results obtained for other aspects of semantic interpretation, such as word sense disambiguation (e.g., Swinney, 1979)

Karen poured a drink for Emily and then {Karen, she} put the bottle down.

Probe (Karen, Emily)

Massimo Poesio:

Point: all antecedents accessed

Marslen-Wilson, 1975: interpretation as a parallel process that simultaneously exploits info at all levels

This effect of ambiguity may be worth mentioning as one of the factors affecting the choice of expression in Lec 2 (as done by Ariel)

Massimo Poesio:

Point: all antecedents accessed

Marslen-Wilson, 1975: interpretation as a parallel process that simultaneously exploits info at all levels

This effect of ambiguity may be worth mentioning as one of the factors affecting the choice of expression in Lec 2 (as done by Ariel)


Explicit vs. non explicit antecedents Explicit vs. non explicit antecedents

The easier it is to identify the antecedent, the quicker the anaphor is processedE.g., Haviland and Clark 1974: anaphors with explicit antecedents easier to process

But cfr. results on UNHERALDED PRONOUNS (= no explicit antecedent) (Greene, Gerrig, McKoon and Ratcliff, 1994)Also cfr. Garrod and Sanford 1982 ‘drive’ examples (Garrod and Sanford 1994, Garnham)

Also, Garrod and Sanford, 1977: when anaphor more removed from antecedent, slower (the tank / the vehicle vs. the car / the vehicle)

Massimo Poesio:

Perhaps skip this?

Massimo Poesio:

Perhaps skip this?


Factors that play a role in antecedent Factors that play a role in antecedent search: form of anaphoric expression search: form of anaphoric expression (`bottom-up strategies’)(`bottom-up strategies’)

Contrasts like the following suggest that the type of anaphoric expression determines the search procedure:

Keith drove to London yesterday. The car kept breaking down. Keith drove to London yesterday. ?? It kept breaking down.

Or Partee classic ‘marble’ example:I dropped ten marbles and found nine of them.

?? It is probably under the sofa.The missing marble is probably under the sofa.

Massimo Poesio:

Need to rethink this discussion a bit

This should just become the beginning of ‘interpreting anaphoric expressions’, continuing into incrementality and parallelism

E.g., discuss more linguistic evidence such as proposals by Linde (1979) and Passonneau (1993) that ‘that’ signals transitions; and similar proposals by Fox (1984) (see p. 15 of Rosemary’s new version of chapter 6) before discussing the psych evidence, and ONLY THEN go on to Gundel et al’s hierarchy and Grosz and Sidner’s claim

Clearly, the search for antecedents is not a simple matter of finding the one antecedent that matches.

Massimo Poesio:

Need to rethink this discussion a bit

This should just become the beginning of ‘interpreting anaphoric expressions’, continuing into incrementality and parallelism

E.g., discuss more linguistic evidence such as proposals by Linde (1979) and Passonneau (1993) that ‘that’ signals transitions; and similar proposals by Fox (1984) (see p. 15 of Rosemary’s new version of chapter 6) before discussing the psych evidence, and ONLY THEN go on to Gundel et al’s hierarchy and Grosz and Sidner’s claim

Clearly, the search for antecedents is not a simple matter of finding the one antecedent that matches.


Evidence suggesting that different Evidence suggesting that different NPs are interpreted in a different NPs are interpreted in a different wayway

The time it takes to resolve pronouns and definite descriptions depends on the number of antecedents (Fredriksen, 1981; Garnham, 1989); this is not the case with proper names (Gordon et al, 1999)The experiments by Garrod, Freudenthal and Boyle (1994) suggest that definite descriptions and proper names are always resolved, but pronouns sometimes aren’t (similar claims made by Green, McKoon, and Ratcliff, 1992)

Massimo Poesio:

First item based on discussion by Garnham, p. 87

Add discussion of Vonk Hustinx and Simons 1992? (cfr. Rosemary’s version of chapter 6, p. 16-17)

Check Garrod’s paper

Plus evidence supporting claim that pronouns and definite descriptions interpreted differently? Fletcher, 1984; Marslen-Wilson and Tyler, 1982? (reference by Gordon et al 1993) Or put that together with focusing?

Massimo Poesio:

First item based on discussion by Garnham, p. 87

Add discussion of Vonk Hustinx and Simons 1992? (cfr. Rosemary’s version of chapter 6, p. 16-17)

Check Garrod’s paper

Plus evidence supporting claim that pronouns and definite descriptions interpreted differently? Fletcher, 1984; Marslen-Wilson and Tyler, 1982? (reference by Gordon et al 1993) Or put that together with focusing?


Theoretical accounts of the role of Theoretical accounts of the role of the type of referring expressionthe type of referring expression

Grosz and Sidner (1986): pronoun antecedents founds in the LOCAL FOCUS, antecedents of full NPs in the GLOBAL FOCUS (see Clark and Sengul, 1979; next week?) Gundel Hedberg and Zacharski (1993): GIVENNESS HIERARCHY (discussed on Monday):

It, he, she: IN FOCUSThis, That, This N: ACTIVATEDThat N: FAMILIARDefinite descriptions: UNIQUELY IDENTIFIABLEA N: IDENTIFIABLE

For the moment, we concentrate on PRONOUNS (some of the notions discussed play a role for other expressions as well – cfr. Sidner 1979). More on definites in Week 3.


Factors that play a role in pronoun Factors that play a role in pronoun interpretationinterpretation

`Constraints’ vs. ‘Preferences’Constraints:

Morphological information (gender, number, case)Syntactic information (e.g., binding )Semantic information (cfr. DRT)

Preferences:Commonsense knowledgeSyntactic preferences (e.g., subject assignment, parallelism – tomorrow)Discourse factors? (tomorrow, rest of the week)

Classification into ‘constraints’ and `preferences’ not always very easy

Massimo Poesio:

The discussion of factors go into separate point? E.g., with non-salience based methods? Or separate chapter?

Massimo Poesio:

The discussion of factors go into separate point? E.g., with non-salience based methods? Or separate chapter?


Gender and pronouns: psych Gender and pronouns: psych evidenceevidence

Ehrlich, 1980: interpretation is faster when gender disambiguates

Jane blamed Bill because he spilt the coffee.John blamed Bill because he spilt the coffee

Corbett and Chang 1983: both antecedents still activated at the end of the sentence only when gender doesn’t disambiguateGarnham, Oakhill, Ehrlich, and Carreiras: effects are equally rapid in languages with ‘semantic’ gender (such as English) and in languages with ‘syntactic’ gender (Italian, Spanish, French)Cacciari, Carreiras, and Cionini: in Italian, pronouns referring to EPICENES – words that can refer to individuals of either gender (‘la vittima’) - interpreted more quickly if match the gender (‘la donna / la vittima’ vs. `l’uomo/ la vittima’)

Massimo Poesio:

Rosemary’s notes in chapter 6: use of gender info depends on task (not used if only sentence comprehension tested)

Massimo Poesio:

Rosemary’s notes in chapter 6: use of gender info depends on task (not used if only sentence comprehension tested)


But …But …

Effect of gender less strong when it conflicts with other strong preferencesE.g., Caramazza et al, 1977; Ehrlich 1980

(faster with he than with she)

Steven blamed Jane because he/she spilled the coffee


NumberNumber

Garrod and Sanford (1982): singular and plural pronouns referring to conjuncts interpreted equally easily in subject position, but plurals interpreted more easily in object position:

It was a fine Saturday morning.John and Mary went into town. She / they / Mary wanted some new clothes. The shop attendant told her / them / Mary to wait.

Gordon, Hendrick, Ledoux and Yang (1999): plural pronouns referring to antecedents introduced by conjunct interpreted more easily than singular pronoun referring to either conjunct:

Pam and Stan asked the usherette for assistance. She / they quickly followed the usherette to their seats.

Massimo Poesio:

Note that these experiments are not exactly about constraints, but about

the effect of plural form on search

Massimo Poesio:

Note that these experiments are not exactly about constraints, but about

the effect of plural form on search


Binding ConstraintsBinding Constraints

Lees and Klima (1963), Langacker (1969), Lasnik (1976), Reinhart (1976, 1983), Chomsky (1981, 1986): syntactic constraints limit intrasentential anaphoric relations

The Binding Theory (Chomsky, 1981):Principle A: anaphors (= reflexives) must have an antecedent in their governing categoryPrinciple B: pronouns cannot have an antecedent in their governing categoryPrinciple C: R-expressions (PNs, etc) must be free everywhere

Bill Clinton hates him

Bill Clinton hates himself

*Bill Clinton hates him


Binding constraints: evidenceBinding constraints: evidence

Nicol and Swinney (1989): a cross-modal priming experiment

Associates of ‘boxer’, ‘skier’ and ‘doctor’ presented after anaphorsPriming only for words consistent with binding theory

Gordon and Hendrick (1997):Good evidence that reflexives and pronouns are in complementary distribution (as predicted)John met John’s roommates at the restaurant. John’s roommates met John at the restaurant. He met John’s roommates at the restaurant.His roommates met John at the restaurant.

The boxer told the skier that the doctor for the team would blame himself for the recent injury.The boxer told the skier that the doctor for the team would blame him for the recent injury.

Massimo Poesio:

Check Gordon and Hendrick

Massimo Poesio:

Check Gordon and Hendrick


Semantic constraintsSemantic constraints

Scope limits accessibility:If a man owns a donkey, he beats it.*If every man owns a donkey, he beats it.

X Y W Z

Man(X)

Donkey(Y)

Owns(X,Y)

W=X

Z=Y

Beats(W,Z)

X

Man(X)

W Z

W=X

Z=Y

Beats(W,Z)

Donkey(Y)

Owns(X,Y)

Y

Massimo Poesio:

No evidence?

Massimo Poesio:

No evidence?


Preferences, I: Commonsense Preferences, I: Commonsense knowledgeknowledge

Sidner (1979):The city council refused the women a permit because they feared violence.The city council refused the women a permit because they advocated violence

BRISBANE – a terrific right rip from Hector Thompson dropped Ross Eadie at Sandgate on Friday night and won him the Australian welterweight boxing title. (Hirst, 1981)Ellipsis (Hirst, 1981)

Ross loves his wife and Daryel does tooNadia is able to twitch her nose and Ross is too.


Inference in anaphora resolutionInference in anaphora resolution

Haviland and Clark 1974: best-known evidence of backward inference

Garrod and Sanford 1981, etc: it takes longer to process a bird .. the robin than a robin … the bird or a bird .. the birdCentral question in psychological literature: is there any clear evidence for forward inference?

Bradford et al: inferences really carried out right away?

McKoon & Ratcliff 1992 ‘minimalist theory of inference’?Do not infer broom from sweep the yard

Corbett and Dosher: ‘shovel’ good cue for ANY sentence involving digging a hole (even if digging with a pitchfork)

We got some beer out of the trunk. The beer was warm.

We checked the picnic supplies. The beer was warm.

Massimo Poesio:

Check McKoon and Ratcliff

Massimo Poesio:

Check McKoon and Ratcliff


Context also includes `linguistic’ Context also includes `linguistic’ informationinformation

The previous discussion suggests that context must include (at least provisionally) some linguistic information as well:

E.g., gender for pronouns“la table” <- “elle”“le meuble” <- “il”

Or memory of antecedents for ellipsis:John has spoken to Mary, and Bill has too

Massimo Poesio:

Move this AFTER discussing commonsense-based knowledge? (Or at least, after discussing disamb factors?)

Massimo Poesio:

Move this AFTER discussing commonsense-based knowledge? (Or at least, after discussing disamb factors?)


Mental Models + Linguistic Mental Models + Linguistic representationsrepresentations

Johnson-Laird, 1983;Kintsch and van Dijk, 1983:Mental models + linguistic representation

Van Dijk and Kintsch, 1983: understanding a discourse results in three distinct ‘memory traces’:

The SURFACE FORMThe PROPOSITIONAL TEXT BASEThe SITUATION MODEL

See also Grosz and Sidner, 1986:`Linguistic level’Intentional levelAttentional level


CRT (Poesio, 1991, 1994; Poesio and CRT (Poesio, 1991, 1994; Poesio and Traum, 1997)Traum, 1997)

M W Y Z E

man(M)

woman(W)

room(Z)

Y = M +W

E: entered(Y,Z)

U1 U2 U3 U4 U5 U6 U7 CE1 K1

U1: utter(A,”a man”)

Syn(U1) = [cat=NP,num=sg]

Generate(U7,CE1)

CE1: assert(A,K)

K1 =

U7

U1 U2 U3 U4

U5 U6


CRT (Poesio, 1991, 1994; Poesio and CRT (Poesio, 1991, 1994; Poesio and Traum, 1997)Traum, 1997)

M W Y Z E

man(M)

woman(W)

room(Z)

Y = X+W

E: entered(Y,Z)

U1 U2 U3 U4 U5 U6 U7 CE1 K1

U8: utter(A,”the man”)

Syn(U8) = [cat=NP,num=sg]

Generate(U10,CE2)

CE2: assert(A,K2)

elaboration(CE1,CE2)

K1 =

U10

U8 U9

U8 U9 U10 CE2 K2

X S

man(X)

S: sat-down(X)

X = M

K2 =

………

Massimo Poesio:

See also: SDRT

Massimo Poesio:

See also: SDRT


How long do these linguistic How long do these linguistic representations last?representations last?

Sacks, 1967; Jarvella, 1971: short-livedJarvella 1971: while current sentence is readily available for verbatim recall, sentence one back is no

But others (e.g., Kintsch and Bates, 1977) later showed that the representation of at least some sentences in short-term memory includes at least some surface information Discussion in Fletcher, 1994

Massimo Poesio:

Skip unless lots of time

Massimo Poesio:

Skip unless lots of time


Context also contains: discourse Context also contains: discourse structurestructure

Meyer, 1975, Kintsch and van Dijk 1978:Subordination relations affect recall

Stevenson, Crawley and Kleinman, 1994: rhetorical relations affect salience (on Wed)Kintsch and van Dijk, 1978; Stevenson et al, 2000: parts of discourse model connected by referential and rhetorical relationsCAUSAL RELATIONS:

The stone hit the window. It broke. Can be represented in DRT

`TRUE’ RHETORICAL RELATIONS (e.g., EVIDENCE)Connors used kevlar sails. I read it in The Guardian.

Other extensions of DRT provide this (e.g., SDRT – Asher, 1993; Asher and Lascarides, 1998)

Massimo Poesio:

In book, we may have a discussion of ‘structure in discourse models’ in chap anaphora mentioning theories of discourse structure motivated by work on recall and memory, and then a discussion of claims like Grosz’ and Reichman’s that discourse structure affects salience in chap salience

The discussion should include material from Gordon survey, including discussion of `event based’ models of structure like story grammars, Kintsch and van Dijk, and perhaps causal networks; and maybe also mention alternative of ‘intentional models’

Massimo Poesio:

In book, we may have a discussion of ‘structure in discourse models’ in chap anaphora mentioning theories of discourse structure motivated by work on recall and memory, and then a discussion of claims like Grosz’ and Reichman’s that discourse structure affects salience in chap salience

The discussion should include material from Gordon survey, including discussion of `event based’ models of structure like story grammars, Kintsch and van Dijk, and perhaps causal networks; and maybe also mention alternative of ‘intentional models’


We will mostly ignore these We will mostly ignore these complexities … complexities …

And assume a vanilla DRT notion of discourse model unless necessary


The time-order of sentence The time-order of sentence processingprocessing

GARDEN-PATH phenomena shows that parsing is INCREMENTALThe horse raced past the barn fell (Bever, 1974)

Frazier and Rayner, 1982:

(encounter difficulty with second, but not first)

Marslen-Wilson 1973, 1975: semantic information ALSO accessed immediatelySwinney, 1979: lexical access incrementalJust and Carpenter,1980: IMMEDIACY HYPOTHESIS

“Every word encountered should be processed to the deepest level possible before the eye moves on to the next word”

Sam loaded the boxes on the cart …

BEFORE LUNCH / ONTO THE VAN

Massimo Poesio:

Check Marslen-Wilson 1975

Massimo Poesio:

Check Marslen-Wilson 1975


The time course of anaphoric The time course of anaphoric processingprocessing

Anaphoric garden-paths are also possibleIf an incendiary bomb drops near you, don’t lose your head. Put it in a bucket and cover it with sand.

Hobbs, 1974: effect of ellipsis (but evidence ???)

Just and Carpenter (1977), Ehrlich (1980), Gernsbacher (1989): pronoun interpretation is INITIATED when the pronoun is encountered.Empirical evidence that definite descriptions are interpreted incrementally: the experiments of Tanenhaus et al (1995)

My uncle doesn’t have a spouse, but your aunt does, and he is lying on the floor.

Massimo Poesio:

Add Dilbert? Else, Woodehouse examples from Caroline

Hobbs example n ot terribly convincing

Massimo Poesio:

Add Dilbert? Else, Woodehouse examples from Caroline

Hobbs example n ot terribly convincing


Incrementality in definite Incrementality in definite descriptions: Tanenhaus et al (1995) descriptions: Tanenhaus et al (1995)

Pick up the red triangle that is below the green circle


Underspecification in syntactic Underspecification in syntactic processingprocessing

Frazier and Rayner, 1987: cases of local syntactic ambiguity that do not trigger immediate commitment

(subjects spend more time fixating unambiguous examples than ambiguous ones)

I know that the DESERT TRAINS young people to be especially though

I know that the DESERT TRAINS are especially though on young people

I know that THIS desert trains young people to be especially though

I know that THESE desert trains are especially though on young people

Massimo Poesio:

Notice that there is a contradiction here with earlier claim that it took longer to process ambiguous expressions – unless we claim that this type of expressions are treated differently!)

Massimo Poesio:

Notice that there is a contradiction here with earlier claim that it took longer to process ambiguous expressions – unless we claim that this type of expressions are treated differently!)


Underspecification in semantic Underspecification in semantic processingprocessing

Frazier and Rayner, 1990

After they were scratched, the records were closely guarded. After the takeover, the records were closely guarded. The records were closely guarded after they were scratched. The records were closely guarded after the takeover.

Lying in the rain, the newspaper was destroyed. Managing advertising so poorly, the newspaper was destroyed. Unfortunately the newspaper was destroyed, lying in the rain.Unfortunately the newspaper was destroyed, managing advertising so poorly.


The `Moses Effect’The `Moses Effect’

This book fills a much-needed gap (Johnson-Laird, 1981)No head injury is too small to be ignored. (Wason and Reich, 1979)How many animals of each sort did Moses put on the ark? (Erickson and Mattson, 1981)Barton and Sanford (1993):

There was a tourist flight travelling from Vienna to Barcelona. On the last leg of the journey, it developed engine trouble. Over the Pyrenees, the pilot started to lose control. The plane eventually crashed right on the border. Wreckage was equally strewn in France and Spain. The authorities where trying to decide where to bury the survivors.

What is the solution to this problem?


Pronouns: begin immediately, Pronouns: begin immediately, possibly delaypossibly delay

Gernsbacher (1989), extending work by Corbett and Chang (1983)

Garrod and Sanford (1985): spelling error detection taskWith proper names and definite descriptions: subjects take longer to detect spelling error with inconsistent verbWith pronouns: delayed recognition effect only with pronouns referring to ‘thematic subject’ of passage

Garrod, Freudenthal and Boyle (1993): eye-tracking study

1. Bill handed John some tickets to a concert but {Bill / he} took the tickets back immediately.

2. Ann predicted that Pam would lose the track race, but {Pam / she} came in first very easily.

With full names: non-antecedent deactivated immediately after the anaphor is processedWith pronouns: non-antecedent deactivated only at the

end of the sentence

Massimo Poesio:

Gordon and Scearce seem to show that in some cases at least pronouns

ARE resolved immediately, even in same-gender contexts: because more

evidence?

Massimo Poesio:

Gordon and Scearce seem to show that in some cases at least pronouns

ARE resolved immediately, even in same-gender contexts: because more

evidence?


Garrod and Sanford, 1985Garrod and Sanford, 1985

A dangerous incident at the pool

Elizabeth was an inexperienced swimmer and wouldn’t have gone in if the male lifeguard hadn’t been standing by the pool. But as soon as she got out of her depth she started to panic and was her hands about in a frenzy.

(a) Within seconds Elizabeth senk (sank) into the pool.

(b) Within seconds Elizabeth jimped (jumped) into the pool.

(c) Within seconds the lifeguard senk into the pool.

(d) Within seconds the lifeguard jimped into the pool.

(e) Within seconds she / he senk into the pool.

(f) Within seconds she/ he jimped into the pool.


Garrod, Freudenthal & Boyle, 1994Garrod, Freudenthal & Boyle, 1994

Elizabeth1/(Alexander1) was an inexperienced swimmer and wouldn’t have gone in if the male lifeguard2 hadn’t been standing by the pool. But as soon as she/(he) got out of her/(his) depth she/(he) started to panic and wave her hands aboutin a frenzy…..

(1)Within seconds she1 sank1 into the pool (+Focus+Gender)(2)Within seconds she1 jumped2 into the pool(3)Within seconds he1 sank1 into the pool (+Focus-Gender)(4)Within seconds he1 jumped2 into the pool(5)Within seconds he2 jumped2 into the pool (-Focus+Gender)(6)Within seconds he2 sank1 into the pool


Garrod et al. (1994) FindingsGarrod et al. (1994) Findings

Immediate Focus/Gender mismatch effect, so gender has an immediate effect (Bonding, Sanford et al. ‘83: Garrod & Terras,

2000)

But resolution is delayed except when Gender and Focus jointly identify pronoun antecedent


Arnold, Eisenband et al (2000)Arnold, Eisenband et al (2000)

Donald is bringing some mail to {Mickey/Minnie}(He’s sauntering down the hill, )While a violent storm is beginning. He’s/She’s carrying an umbrella…..


Findings from Arnold, Eisenband et al Findings from Arnold, Eisenband et al (2000)(2000)

Expt1&2: Gender + Focus, Gender alone or Focus alone produce immediate pronoun resolution (i.e., fixation on the target within 400 msecs. of pronoun onset)

Conclusion: Difference between resolution process with surrogate models (G,F&B, ‘95) and interface models(A, E, et al, 2000)


Commonsense knowledgeCommonsense knowledge

The Hodja was walking home when a man came up behind him and gave him a thump on the head. When the Hodja turned round, the man began to apologize, saying that he had taken him for a friend of his. The Hodja, however, was very angry at this assault upon his dignity, and dragged the man off to court. It happened, however, that his assailant was a close friend of the cadi [magistrate], and after listening to the two parties in the dispute, the cadi said to his friend: “You are in the wrong. You shall pay the Hodja a farthing damages.”

His friend said that he had not that amount of money on him, and went off, saying he would get it. Hodja waited and waited, and still the man did not return. When an hour had passed, the Hodja got up and gave the cadi a mighty thump on the back of his head. “I can wait no longer”, he said. “When he comes, the farthing is yours.”

(From Downing, Tales of the Hodja, 1964 (reported in Hirst (1981)))

Massimo Poesio:

Some of these cases accounted for in terms of constraints

The Maupin example probably better

Massimo Poesio:

Some of these cases accounted for in terms of constraints

The Maupin example probably better


`Pure’ commonsense knowledge `Pure’ commonsense knowledge methods in AImethods in AI

Early work: Rieger (1972), Charniak (1972)Wilks (1974): preference semantics

TYPE A resolution: ‘fuzzy matching’ between antecedent type and property asserted of pronoun

Monkeys animate -> more likely to be hungryBananas a fruit -> more likely to be ripe

If type A fails, apply analytic inference (type B) and deeper reasoning (type C); if both fail, use focus

Hobbs 1974: ‘semantic-based’ algorithm

Give the bananas to the monkeys although they are not ripe, because they are very hungry

Massimo Poesio:

Check Charniak

Check Carter as well

Notice that ‘type A’ resolution looks a lot like ‘property sharing’ a la Kameyama / Smyth 1994

Massimo Poesio:

Check Charniak

Check Carter as well

Notice that ‘type A’ resolution looks a lot like ‘property sharing’ a la Kameyama / Smyth 1994


Problems with `pure’ commonsenseProblems with `pure’ commonsense

Very difficult to discriminate between arguments on the basis of commonsense knowledge only.

Number forty-two gets the ball from thirty-four; he quickly moves forward

Cases in which Wilks’ algorithm would predict the wrong interpretation:

John can open Bill’s safe – he knows the combination (Hobbs, 1979)Nadia hastily swallowed the licorice, and followed Ross to the bathroom. She stared in disbelief at the water coming out of the tap: it was black. (Hirst, 1981)

Algorithms such as Wilks can’t explan why examples such as the following are funny:

If an incendiary bomb drops near you, don’t lose your head. Put it in a bucket and cover it with sand. John left the window and drank the wine on the table. It was brown and round.

At the present time, these methods are impossible to evaluate by building a system and running it over a large corpus


Psychological evidencePsychological evidence

No question that commonsense knowledge is USEDFor pronouns: interference with gender observed by Caramazza et al, Stevenson Crawley and Kleinman, etcFor definite descriptions: essential for bridging references (e.g., Haviland and Clark, 1974; Garrod and Sanford, 1981, 1982, … ) and for references to visual situation (cfr. Tanenhaus et al)

As said in previous lecture, research has focused on WHEN it is used: immediately or ‘on demand’

Haviland and Clark vs. Garrod and Sanford

On Wednesday: use of commonsense knowledge to assess plausibility of hypotheses

Massimo Poesio:

Actually, MORE can be said:

1. the Tanenhaus experiments (diff between ‘world there’ and ‘encyclopedic knowledge’?

2. the Marslen-Wilson / Tyler work

3. ?? the Brennan examples??

4. interaction with gender already discussed

Massimo Poesio:

Actually, MORE can be said:

1. the Tanenhaus experiments (diff between ‘world there’ and ‘encyclopedic knowledge’?

2. the Marslen-Wilson / Tyler work

3. ?? the Brennan examples??

4. interaction with gender already discussed


RecencyRecency

Clear preference for pronouns to be interpreted as referring to most recent antecedents:

Recency can often beat commonsense knowledge:The companies had a lot of money and spent lavishly on their boat. The boys, in contrast, built their boat on a tight budget. They knew they would win the race easily. (Allen, 1995)

Quantitative data support the intuition:Hobbs (1974): 98% of antecedents in current or previous sentenceClark and Sengul (1979): antecedents in current or previous sentence resolved much faster than antecedents in previous sentences

Most basic models of pronoun resolution in NLP attempt to capture this intuition

John and Mary went to the library. It was quite full. The librarian sat behind a desk.He smiled at Mary.

Massimo Poesio:

James: even more so for ellipsis,p. 429 (but example not completely convincing)

Recency example not terribly convincing either.

Massimo Poesio:

James: even more so for ellipsis,p. 429 (but example not completely convincing)

Recency example not terribly convincing either.


Recency-based algorithmsRecency-based algorithms

Basic history list algorithm: keep list of discourse enties in order of mention (most recent first)To resolve a pronoun, find most recent antecedent that matches in gender and number and satisfies binding constraints.

One evaluation: Tetreault (2001): Use the algorithm to assign an interpretation to about 2000 pronouns in two domains (195 newspaper articles and 3 narratives) ‘naïve recency’ algorithm interprets about 60% of pronouns correctly (as opposed to 76% correct for Hobbs’ algorithm, described below)

Massimo Poesio:

Evaluate using GNOME corpus?

Classic counterexamples?

Massimo Poesio:

Evaluate using GNOME corpus?

Classic counterexamples?


Problems with ‘pure’ recencyProblems with ‘pure’ recency

Charniak (1972):

John can open Bill’s safe – he knows the combination (Hobbs, 1979) When Sue went to Nadia’s home for dinner, she ate sukiyaki au gratin. (Hirst, 1981)Classic Wilks (1974) example (unintended joke) John left the window and drank the wine on the table. It was

brown and round.

Jack invited Janet to his birthday party.Janet wondered if Jack would like a kite. But Bill said Jack already had a kite. Jack would make her take it back.

Massimo Poesio:

Note that Wilks’ example is a very good argument for Hobbs’ algorithm (pace Hirst)

Massimo Poesio:

Note that Wilks’ example is a very good argument for Hobbs’ algorithm (pace Hirst)


Empirical evidence against ‘pure’ Empirical evidence against ‘pure’ recencyrecency

Corbett and Chang (1983), Gernsbacher (1989): advantage of first mention

Effect of first mention also observed by Crawley, Stevenson and Kleinman (1990) by Stevenson, Crawley, and Kleinman (1994), and Gordon et al (1993), inter alia. Conclusion: Although sentences are considered right-to-left, NPs in clauses are considered left-to-right (see also Hobbs algorithm below)Relevant again when talking about Sidner’s ‘RECENCY RULE’

NP1:Bill handed John some tickets to a concert but he took the tickets back immediately.

NP2: Ann predicted that Pam would lose the track race, but she came in first very easily.

Massimo Poesio:

These materials from Gernsbacher 1989. Idea: reading time significantly faster when NP1 (as in 1) than in NP2 (as in 2)

Check Garnham

Matthews and Chodorow p. 246: evidence that search is left-to-right within the sentence (Corbett and Chang), right-to-left in the context (Clark and Sengul)

Massimo Poesio:

These materials from Gernsbacher 1989. Idea: reading time significantly faster when NP1 (as in 1) than in NP2 (as in 2)

Check Garnham

Matthews and Chodorow p. 246: evidence that search is left-to-right within the sentence (Corbett and Chang), right-to-left in the context (Clark and Sengul)


Syntactic prominence: `Subject Syntactic prominence: `Subject assignment’assignment’

Hirst example shows that often discourse entities in `syntactically prominent’ positions such as subject preferred over more recentThis preference for pronouns to occur in subject position, and to refer to entities in subject position, is one of the most robust effects in the literature on pronoun interpretationAcross most corpora, about 60-70% of pronouns occur in subject position; about 70% of pronouns in subject position have an antecedent in subject position

Massimo Poesio:

Mention that this is the most basic type of

`salience’

Massimo Poesio:

Mention that this is the most basic type of

`salience’


Psychological evidence on subject Psychological evidence on subject assignmentassignment

About 70% of pronouns in subject position are interpreted as referring to an antecedent in subject position; as well as about 60% of pronouns in non-subject position in non-parallel sentences (Broadbent, 1973; Clancy, 1980; Crawley, Kleinman, and Stevenson, 1990)Faster reading time for pronouns in subject position referring to antecedents in subject position (Fredriksen, 1981; Crawley, Kleinman, and Stevenson, 1990; MacDonald and MacWhinney, 1995)


Algorithms exploiting subject Algorithms exploiting subject preferencespreferences

Winograd’s SHRDLU (1972):Check all possibilities and assign a global score rather than simply find the first matchScore incorporates syn component: entities in subj position higher score than entities in object position, in turn ranked more highly than entities in adjunct positionPerformance made more impressive by including solutions to a number of complex cases, such as reference to events (Why did you do it?) – often ad hoc


Extensions of the idea of syntactic Extensions of the idea of syntactic preferencespreferences

Syntactic ParallelismHobbs’ algorithm


ParallelismParallelism

A number of researchers found evidence that the position of the pronoun affect its interpretationSheldon (1974):

Studied how 4- and 5-year-olds interpret relative clausesClaim: many of their mistakes could be explained by assumption that they adopted a PARALLEL FUNCTION STRATEGY: preference for individuals to play same function in main clause and relative clause

John saw a man who he liked

Kameyama (1986): PROPERTY SHARINGPronouns must match their antecedents in function as well

Crawley, Stevenson and Kleinman (1990): the early studies only considered pronouns in subject position; need to look at pronouns in non-subject position, as wellSmyth (1994): look at both

Massimo Poesio:

Check actual Sheldon data

Possibly move this to the end of this lecture (after focusing)

Massimo Poesio:

Check actual Sheldon data

Possibly move this to the end of this lecture (after focusing)


Parallel Function vs. Parallel OrderParallel Function vs. Parallel Order

Smyth (1994), Stevenson, Nelson and Stenning (1995): need to distinguish between PARALLEL FUNCTION STRATEGY and PARALLEL ORDER STRATEGY

Results:Stronger effect: preference for subject pronouns to refer to antecedents in subject position (SUBJECT ASSIGNMENT)Parallelism effects stronger when parallelism of functionPragmatic effects easily override parallelism

PARALLEL FUNCTION: John punched Sammy on the nose and

he kicked Ellen in the backEllen kicked him in the back

PARALLEL ORDER: Mary helped Priscilla change the wheel and

she talked to Graham without interestGraham talked to her without interest

Massimo Poesio:

Smyth (1994): account in terms of property sharing

Need to mention Kehler’s claims (cfr. question in class)

Massimo Poesio:

Smyth (1994): account in terms of property sharing

Need to mention Kehler’s claims (cfr. question in class)


(Semantic) parallelism and ellipsis(Semantic) parallelism and ellipsis

(Dalrymple, Pereira, and Shieber, 1991; Prust, 1992; Kehler, 1993; Asher, 1993): ellipsis resolution is based on parallelism

John revised his paper before the teacher did.

Hobbs and Kehler (1997): a general theory of parallelism claimed to account for both ellipsis and pronoun resolution (especially paycheck pronouns)

Two fragments of discourse stand in a parallel relation if they describe similar propertiesSIMILAR[P(e1,x1,…xn),P(e2,y2,….yn)]:

P(e1,x1,…xn) -> Q(e1,x1,…xn)P(e2,y1,….yn) -> Q(e2,y1,….yn)COREF(xi,yi) OR SIMILAR(xi,yi);

SIMILAR[Xi,Yi]: if other ‘inferentially independent’ properties are similar


ReadingsReadings

Garnham, chapters 3-6


ReferencesReferences

Good general discussions of anaphora and anaphora interpretation:

Alan Garnham – Mental Models and the interpretation of anaphora – Psychology Press, 2001 (excellent survey especially for the psychological part) Simon Garrod and Tony Sanford, Resolving Sentences in a Discourse Context. Chapter 20 of M. Gernsbacher(ed), Handbook of Psycholinguistics, Academic Press, 1994. (Incrementality and underspecification)Graeme Hirst - Anaphora in Natural Language Understanding: A Survey – Springer-Verlag, 1981 (a bit outdated now)Hans Kamp and Uwe Reyle – From Discourse to Logic – Kluwer, 1993 (comprehensive intro to DR, good on semantic constraints)


Other referencesOther references

Bransford, J. D. and Franks, J. J. The abstraction of linguistic ideas. Cognitive Psychology, v. 2, 331-350, 1971.Bransford, J. D., Barclay, J. R. and Franks, J. J. Sentence memory: a constructive vs interpretive approach. Cognitive Psychology, v. 3, 193-209, 1972.Clark, H. H. Bridging. In P. Johnson-Laird and P. C. Wason (eds), Thinking: Readings in Cognitive Science. Cambridge, 1977Clark, H. H. and Sengul, C. J. In search of referents for noun phrases and pronouns. Memory and Cognition, v. 7, 35-41, 1979Corbett, A. T. and Chang, F. R. Pronoun disambiguation: accessing potential antecedents. Memory and Cognition, v. 11, 283-294, 1983.Van Dijk, T. A. and Kintsch, W. Strategies of Discourse Comprehension. Academic Press, 1983.Fodor, J. A, Bever, T.G., and Garrett, M. F. The Psychology of Language. Mc Graw –Hill, 1974. Haviland, S. E. and Clark, H. H. What’s New? Journal of Verbal Learning and Verbal Behavior, v. 13, 512-521,1974.


References (cont’d)References (cont’d)

Johnson-Laird, P. N. Mental Models. Cambridge, 1983.Karttunen, L. Discourse Referents. In J. Mc Cawley (ed),Syntax and Semantics: v. 7. Academic Press, 1976Kintsch. W. and van Dijk, T. A. Towards a model of discourse comprehension and production. Psychological Review, v. 85, 363-394, 1978Tanenhaus, ….B. L. Webber. A formal approach to discourse anaphora. Garland, 1978.

gundel & poesio - computational approaches to reference

Documents

e mezza

appropriate discourse

prendi quello e mettilo

descrizioni definite

context verbal

definite descriptions

mario e stato visto

indefinite pronouns