Computational Approaches to Reference

1. Computational Approaches to Reference Massimo Poesio (University of Essex) Lecture 4: Centering Theory LSA

2. Today’s lecture • A formalization of the notion of ‘in focus’: Centering • Evidence for centering: • Behavioral • Corpora • Centering-based anaphora resolution LSA

3. Theories of salience & focusing • Fixed number of foci: • Sidner’s theory • Centering • Unbounded: • Unbounded, but no activation • Strube’s S-List 1998, Henschel Cheng & Poesio • Activation-based: • Kantor, Alshawi / Lappin & Leass, Haijcova LSA

4. Massimo Poesio: Gordon survey makes it quite clear that the `local focus’ plays here a role similar to that of Short Term Memory (STM) in the Kintsch and van Dijk model – but interestingly, Gordon himself seems to assume that it’s the stack that corresponds to the STM! Perverse ??? Maybe we should discuss Guindon’s model in chapter centering, as an alternative to the idea of the local focus as a CF list? (Just as Walker’s cache model would be an alternative to the stack model?) The Grosz and Sidner theory of discourse • Central idea: COHERENCE and SALIENCE go hand in hand • Reintroduce the idea of a separation between `local’ and `global’ bal’ aspects of coherence and salience (the LOCAL FOCUS and GLOBAL FOCUS) from Grosz, 1977 • Two separate theories for each component: • Global focus: Grosz and Sidner, 1986 • Local focus: Centering theory (Grosz, Joshi and Weinstein, 1983, 1995) LSA

5. Massimo Poesio: Focus stack not necessarily situation-based The Global Focus • At this level of discourse organization, • Coherence has to do with INTENTIONAL STRUCTURE, I.e., a discourse is perceived as GLOBALLY COHERENT if the intentions expressed by its constituents are related • ATTENTIONAL STRUCTURE is about situations rather than events: GLOBAL ATTENTION is on FOCUS SPACES, subsets of the global knowledge base • Three levels of discourse structure: • LINGUISTIC STRUCTURE (cfr. Van Dijk and Kintsch’s `linguistic structure’ • INTENTIONAL STRUCTURE: intentions associated with segments together with their relations, DOMINANCE and SATISFACTION-PRECEDES • ATTENTIONAL STRUCTURE: a stack of FOCUS SPACES, each associated with an intention, and whose position reflects the relations among intentions LSA

6. Example: the Grosz 1977 `tent’ story • P1: I’m going camping next week-end. Do you have a two-person tent I could borrow? • P2: Sure. I have a two-person backpacking tent. • (3) P1: The last trip I was on there was a huge storm. • It poured for two hours. • I had a tent, but got soaked anyway. • P2: What kind of tent was it? • P1: A tube tent. • P2: Tube tents don’t stand well in a real storm. • P1: True. LSA

7. Example: the Grosz 1977 `tent’ story • P1: I’m going camping next week-end. Do you have a two-person tent I could borrow? • P2: Sure. I have a two-person backpacking tent. • P2: Where are you going on this trip? • P1: Up in the Minarets. • P2: Do you need any other equipment? • P1: No. • P2: OK. I’ll bring the tent in tomorrow. LSA

8. Massimo Poesio: Note how the idea that discourse structure is determined by intentions is different from ideas like kintsch and van Dijk and more in general of ‘situational models’ or ‘event structure’ (cfr. Gordon survey) DOMINATE DSP2: P1 explains why P1 needs tent Intentional structure DSP1: P1 intend to get tent from P2 LSA

9. Intentional structure DSP1: P1 intend to get tent from P2 LSA

10. X1 S1 tent(X1) S1:of(P2,X1) DSP1: P1 intend to get tent from P2 X2 E1 S2 tube-tent(X2) S2:of(P1,X2) E1:washed-up(X2) DOMINATE DSP2: P1 explains why P1 needs tent The Focus Space Stack LSA

11. The Focus Space Stack X1 S1 E3 X3 X4 E4 tent(X1) S1:of(P2,X1) Minarets(X3) E3:go(P1,X3) tent(X4) X4=? E4:bring(P2,X4) DSP1: P1 intend to get tent from P2 LSA

12. Other formalizations of the global focus • Reichman’s ‘context space model’ (1981, 1985) • Context spaces very similar to focus spaces, but with levels of activation • Richer repertoire of relations • Walker’s cache model (1996, 1998) • Replace stack with cache LSA

13. Massimo Poesio: Check Rosemary’s notes: situation is a bit nuanced Good discussion in Garnham, p. 88-91 (although some of the experiments he mentions do not seem terribly relevant) Even better discussion in Gordon survey. But is there any evidence supporting idea of intentional structure as opposed to event structure? (All the evidence mentioned here is from even structure, as is old work by Garrod and Sanford). Gordon mentions correlation with prosody and cue phrases – perhaps Vonk et al? Should also mention that there is real question whether this global structure can be reliably identified Perhaps even mention work with Barbara? And what about ideas from Ali etc that global discourse is entity-structured in certain genres? Some evidence • Clearest evidence for distinction between global focus and local focus: the Clark and Sengul’s experiments discussed in Lecture 1 • Evidence that discourses have a `global organization’ and that discourse segments (and associated episodes) become unaccessible: • Experiments by Anderson et al 1983 suggesting that `temporally closed’ situations become unaccessible • Lesgold, Roth, and Curtis, 1979 • Vonk, Hustin and Simmons 1992 • Corpus work: • Grosz’ own work • Chafe 1979’s analysis of the `pear stories’ • Evidence relevant to the claim that attentional state is a stack: • O’Brien, 1987 • But there is also evidence that antecedents which are ‘too far’ are not accessible any longer (Walker, 1998; O’Brien et al, 1997) LSA

14. Massimo Poesio: Cfr. Knott, Oberlander and Mellish entity coherence as a global organizing principle? The local discourse level • Whereas the global focus theory from Grosz and Sidner 1986 is meant to characterize INTERSEGMENTAL coherence and salience, Centering is meant to characterize INTRASEGMENTAL coherence and salience • The first claim is that what matters most at this level is ENTITY COHERENCE: discourse segments in which successives utterances keep mentioning the same utterances are perceived to be more coherent than discourse segments in which different entities are mentioned each time • A second important claim is that each utterance has a main CENTER, or CB, and that utterances whose CB is the same as the previous one are easier to process • A third claim is that the entities mentioned by an utterance (`realized’) are RANKED (cfr. Sidner’s ordering of DFLs). This ranking determines the CB of subsequent utterances, and changes in ranking also make utterances more difficult to process. LSA

15. The local focus: Centering • Centering is often presented as a development of Sidner, but in fact it is radically different in outlook and fairly different in its details as well • Unlike Sidner’s theory, Centering (Joshi and Weinstein, 1979; Grosz, Joshi and Weinstein, 1983; Grosz, Joshi and Weinstein, 1995) is more of a `linguistic’ theory than a computational one: its primary aim is to develop a vocabulary for talking about local salience and coherence, rather than specific algorithms • The precise specification of many of the central concepts (‘ranking’, ‘utterance’, ‘realization’) is left for further research – indeed, it has been claimed that these concepts may be instantiated in different ways in different languages (Walker et al, 1994) LSA

16. Ranking and local coherence • Grosz et al (1983, 1995): texts that do not have a clear ‘central entity’ feel less coherent (1) a. John went to his favorite music store to buy a piano. b.  He had frequented the store for many years. c.   He was excited that he could finally buy a piano. d.  He arrived just as the store was closing for the day. (2) a. John went to his favorite music store to buy a piano. b. It was a storeJohn had frequented for many years. c. He was excited that he could finally buy a piano. d. It was closing just as John arrived. LSA

17. Local salience and pronominalization • Grosz et al (1995): the CB is also the most salient entity. Texts in which other entities are pronominalized are less felicitous (1) a. Something must be wrong with John. b.  He has been acting quite odd. c.   He called up Mike yesterday. d.  John wanted to meet him quite urgently. (2) a. Something must be wrong with John. b. He has been acting quite odd. c. He called up Mike yesterday. d. He wanted to meet him quite urgently. LSA

18. Massimo Poesio: NB: the one bit that Sidner does not predict is a contrast between c. and e. In the cases d. and f., we have a pronoun in AGENT position referring to an entity in non-AGENT position, and viceversa, which could be claimed to result in processing difficulties. Sidner would also claim that all the pronouns in AGENT position are ambiguous (although not clear what she does with ambiguity) Note also that according to Strube, both entities would be equally ranked. Uniqueness of the center • Grosz et al (1995) argue against Sidner that utterances have a single CB. (1) a. Susan gave Betsy a pet hamster. b.  She reminded her that such hamsters were quite shy. c. She asked Betsy whether she liked the gift. d. Betsy told her that she really liked the gift. e. Susan asked her whether she liked the gift. f. She told Susan that she really liked the gift. LSA

19. Massimo Poesio: Add examples of utterances and CFs! Concepts and definitions • Every UTTERANCE U in a discourse (segment) DS updates the local attentional state, or local focus, which consists of a PARTIALLY RANKED set of discourse entities, or FORWARD-LOOKING CENTERS (CFs) • An utterance U in discourse segment DS updates the existing set of forward-looking centers by replacing it with the set of CFs REALIZED in U, CF(U,DS) (usually simplified to CF(U)) • The most highly ranked CF realized in utterance U is CP(U) (1) u1. Susan gave James a pet hamster. CF(u1) = [Susan,James,pet hamster]. CP(u1) = Susan (2) u2. She gave Peter a nice scarf. CF(u2) = [Susan,Peter,nice scarf]. CP(u2) = Susan LSA

20. The CB: Examples NB: The CB is not always the most ranked entity of the PREVIOUS utterance (1) u1. Susan gave James a pet hamster. CF(u1) = [Susan,James,pet hamster]. CB = undefined CP=Susan (2) u2. She gave Peter a nice scarf. CF(u2) = [Susan,Peter,nice scarf]. CB=Susan. CP=Susan (2’) u2. He loves hamsters. CF(u2) = [James]. CB=James. CP=James … or the most highly ranked entity of the CURRENT one (2’’) u2. Peter gave her a nice scarf. CF(u2) = [Peter,Susan, nice scarf]. CB=Susan. CP=Peter LSA

21. Transitions • Grosz et al proposed that the load involved in processing an utterance depends on whether that utterance preserves the CB of the previous utterance or not, and on whether CB(U) is also CP(U). They introduce the following classification: CENTER CONTINUATION: Ui is a continuation if CB(Ui) = CB(Ui-1), and CB(Ui) = CP(Ui) CENTER RETAIN: Ui is a retain if CB(Ui) = CB(Ui-1), but CB(Ui) is different from CP(Ui) CENTER SHIFT: Ui is a shift if CB(Ui) ≠ CB(Ui-1 LSA

22. Massimo Poesio: Note that you need to establish the CB first – see Walker et al 1994, Kameyama 1998, etc. Utterance classification (0) u0. Susan is a generous person. CF(u0) = [Susan] CB = undefined CP = Susan. (1) u1. She gave James a pet hamster. CF(u1) = [Susan,James,pet hamster]. CB = Susan CP=Susan SHIFT: CONTINUE: (2) u2. She gave Peter a nice scarf. CF(u2) = [Susan,Peter,nice scarf]. CB=Susan. CP=Susan CONTINUE (2’) u2. He loves hamsters. CF(u2) = [James]. CB=James. CP=James SHIFT RETAIN: (2’’) u2. Peter gave her a nice scarf. CF(u2) = [Peter,Susan, nice scarf]. CB=Susan. CP=Peter RETAIN LSA

23. Main claims CONSTRAINT 1: All utterances of a segment except for the first have exactly one CB RULE 1: if any CF is pronominalized, the CB is. RULE 2: (Sequences of) continuations are preferred over (sequences of) retains, which are preferred over (sequences of) shifts. LSA

24. Massimo Poesio: Emphasize what the claims say: these are preferences that make a text easier or harder to read! Violations of the claims • A violation of Rule 1 • Violations of Constraint 1 (1) a. Something must be wrong with John. b.  He has been acting quite odd. CB=John c.   He called up Mike yesterday. CB=John d.  John wanted to meet him quite urgently. CB=John (1) a. Something must be wrong with John. b.  He has been acting quite odd. c.   He called up Mike yesterday. d.  It must have been four o’clock in the morning. CB=undef (1) a. Something must be wrong with John. b.  He has been acting quite odd. c.   He and Susan had a fight yesterday. d.  He didn’t want her to go to the party. CB=John, CB=Susan LSA

25. The parameters of the theory • Grosz et al do not provide algorithms for computing any of the notions used in the basic definitions: • UTTERANCE • PREVIOUS UTTERANCE • REALIZATION • RANKING • What counts as a ‘PRONOUN’ for the purposes of Rule 1? (Only personal pronouns? Or demonstrative pronouns as well? What about second person pronouns?) • One of the reasons for the success of the theory is that it provides plenty of scope for theorizing … LSA

26. The CB • A second CF is singled out as BACKWARD-LOOKING CENTER, CB – Centering’s implementation of the notion of ‘topic’ or, better, ‘main character’ in the sense of Garrod and Sanford (1988) • Originally, the CB was only characterized in intuitive terms. Ever since Grosz, Joshi and Weinstein (1986, 1995), the CB has been DEFINED as follows: • Note however that other characterizations of CB have been proposed – e.g., by Gordon et al (1993) and Passonneau (1993). CONSTRAINT 3: CB(Ui) is the highest-ranked element of CF(Ui-1) that is realized in Ui LSA

27. Utterance and Previous Utterance • Originally, utterances implicitly identified with sentences. Later, however, Kameyama (1998) and others suggested to identify utterances with finite clauses. • If utterances are identified with sentences, the previous utterance is generally easy to identify (except for texts with titles, etc.) But if utterances are identified with finite clauses, there are various ways of dealing with cases like: • (u1) John wanted to leave home (u2) before Bill came home. (u3) He would be drunk as usual. • KAMEYAMA: PREV(u3) = u2. • SURI and MCCOY: PREV(u3) = u1 LSA

28. Realization • A basic question is whether entities can be ‘indirectly’ realized in utterances by an associate (as in Sidner’s algorithm) • (u1) John walked towards the house. • (u2) THE DOOR was open. • A second question is whether first and second person entities are realized: • (u1) Before you buy this medicine, • (u2) you should contact your doctor. • Realization greatly affects Constraint 1. LSA

29. Massimo Poesio: A problem for Strube: how do you account for all that evidence about subject assignment in English? Ranking • The most studied parameter • GRAMMATICAL FUNCTION (Kameyama 1986, Grosz Joshi and Weinstein 1986, Brennan et al 1987, Hudson et al 1986, Gordon et al 1993): • SUBJ < OBJ < OTHERS • A student was here to see John today: A STUDENT < JOHN • INFORMATION STATUS (Strube and Hahn, 1999): • HEARER-OLD < MEDIATED < HEARER-NEW • A student was here to see John today: JOHN < A STUDENT • THEMATIC ROLES (Cote, 1998) • FIRST MENTION / LINEAR ORDER (Rambow, 1993; Gordon et al, 1993) • In Lisa’s opinion, John shouldn’t have done that • Also, the one parameter that is supposed to vary across languages • E.g., ranking in Japanese and Turkish have been claimed to have additional functions (Walker et al 1994; Turan, 1995) LSA

30. Massimo Poesio: On constraint 1: reference to Ehrlich and Johnson-Laird in Gordon et al 1993. Gordon survey also mentions Kintsch, Kozminsky, Streby, McKoon and Keenan 1975, and Manelis and Yekovich 1976 (.p 34) Gordon also sees the 1993 experiments as relevant for Constraint 1 For Strube / Hahn ranking: Sanford Moar and Garrod and our naming paper Empirical evaluations of Centering theory • Some of the evidence about the general architecture of focusing discussed in connection with Sidner’s theory relevant for Centering as well • In particular, evidence concerning interaction with commonsense knowledge, and concerning serial vs. parallel • Constraint 1: supported by work such as Ehrlich &Johnson Laird (1982) • Rule 1: Quite a lot of psychological results, whose connection with Centering is, however, not always so direct: • Hudson, Tanenhaus, and Dell, 1986 • Gordon et al, 1993 and subsequent papers (Gordon and Chan, 1995; Gordon and Scearce, 1995; Gordon et al, 1999) • Brennan, 1995 • Rule 2: no evidence for these preferences (e.g., Gordon et al 1993, Gordon and Scearce 1995) • Several algorithms based on centering theory have been proposed (Brennan et al, 1987; Strube and Hahn, 1999; Tetreault, 2001) and evaluated using annotated corpora • Poesio et al, 2000, 2002: evaluate the claims of the theory by trying various possible parameter settings and finding the one which minimizes the violations of the claims LSA

31. Massimo Poesio: Note that the first entity is most highly ranked both by subject and by implicit causality verbs Ranking: Hudson, Tanenhaus, and Dell • Hudson, Tanenhaus, and Dell, 1986 ran some reading time experiments using materials as follows, in which `Jack’ is made more highly ranked in a. by being the subject and by choosing an NP1 verb • Results: RT(b1) << RT(b2) = RT(b4) << RT(b3) which violates Rule 1 a. Jack apologised profusely to Josh. b1. He had been rude to Josh yesterday. b2. Jack had been rude to Josh yesterday. b3. He had been offended by Jack’s comment. b4. Josh had been offended by Jack’s comment. LSA

32. Massimo Poesio: Remark on the need for an incremental version of centering to evaluate these claims (at least two exists; see also Kehler, 1997) Some comments • Notice that while Centering predicts problems with b3, it does not predict the faster reading times for b1 (see also discussion of Gordon et al’s experiments, next) • In fact, in order to claim that the slow reading time for b3 is consistent with Rule 1, we have to assume that when the subject encounters the pronouns she already knows what the CB is going to be • Furthermore, the materials do not really allow us to tell whether the effect here is due to a true focusing effect, or it’s only a subject assignment preference • Finally, no difference in this case between the predictions according to a theory of ranking based on grammatical function and that proposed by Strube and Hahn (which uses linear order to break ties) LSA

33. Ranking and pronominalization: Gordon, Grosz and Gilliom, 1993 • A series of reading time studies that revealed a REPEATED NAME PENALTY (RNP): an increased reading time when a proper name is used instead of a pronoun PRO-PRO: (1) a. Bruno was the bully of the neighborhood. b.  He chased Tommy all the way home one day. c.   He watched him hide behind a big tree and start to cry. d.  He yelled at him so loudly that all the neighbors came outside. PRO-NAME: (1) a. Bruno was the bully of the neighborhood. b.  He chased Tommy all the way home one day. c.   He watched Tommy hide behind a big tree and start to cry. d.  He yelled at Tommy so loudly that all the neighbors came outside. LSA

34. Ranking and pronominalization: Gordon, Grosz and Gilliom, 1993 NAME-PRO: (1) a. Bruno was the bully of the neighborhood. b.  Bruno chased Tommy all the way home one day. c.   Bruno watched him hide behind a big tree and start to cry. d.  Bruno yelled at him so loudly that all the neighbors came outside. LSA

35. Repeated Name Penalty LSA

36. Massimo Poesio: Exp 2 for b, exp 3 for c Add data supporting claim that first mention and subject same ranking? Ranking and pronominalization: entities subject to RNP • Gordon et al only observed a RNP for entities in SUBJECT position referring to either the FIRST MENTIONED or SUBJECT of the previous utterance (Exp. 2 and 3) • Gordon et al: these results support both Costraint 1 and Rule 1 • They suggest to replace the definition of CB with one based on the RNP • A difference: (2b) above • a. Susan gave Fred a pet hamster. b.  In his / Fred’s opinion, she/Susanshouldn’t have done that.c. She/Susan just assumed that anyone would love a hamster.c’. He/Fred doesn’t have anywhere to put a cage. (2) a. Lisa gave Fred a pet hamster. b.  In her / Lisa’s opinion, an hamster was the best present for him/Fred.c.   In his / Fred’s opinion, She/Lisashouldn’t have done that. LSA

37. A few comments • The RNP is a very interesting result, but a lot of people wonder whether it really makes sense to take it as a verification of Centering, at least in its `classical’ version • Gordon et al didn’t find RNP for entities that would be CBs according to the original definition • Even if we accept Gordon et al’s suggestion that we should modify the theory by dropping the definition in Constraint 3 and adopting the RNP as an operational test for the CB, we would still need to modify Rule 1 – which in its classical form does not REQUIRE the CB to be pronominalized. LSA

38. Massimo Poesio: Skip this for now Check Garnham and survey paper by Gordon Other Gordon experiments • Gordon and Scearce, 1995: focusing generates hypotheses independently from commonsense knowledge • Gordon and Chan, 1995: ranking depends on subjecthood rather than agenthood • Gordon et al, 1999: ranking in complex NPs (coordinated NPs, possessive NPs) depends on structural factors rather than linear order LSA

39. Corpus-based evaluation • Notions from Centering used in a number of studies, especially of the connection between status in the local focus an NP form • Passonneau (1993): comparison of uses of IT and THAT • IT primarily used to refer to LOCAL CENTERs • THAT to entities which are not local centers • Di Eugenio (1992, 1998): `weak’ vs. `strong’ pronouns in Italian • `weak’ pronouns used to maintain CB • `strong’ pronouns for shifting LSA

40. Poesio et al 2000, submitted: A corpus-based evaluation of Centering • Using the GNOME corpus to compare ‘parameter configurations’ using the number of violations of Constraint 1, Rule 1, and Rule 2 as metrics • Can be used on-line: http://cswww.essex.ac.uk/staff/poesio/cbc LSA

41. The trade-off between Constraint 1 and Rule 1: Utterance parameters LSA

42. Massimo Poesio: Have to add here discussion of Tetreault Algorithms based on centering theory • Anaphora resolution: • Brennan, Friedman and Pollard, 1987 (BFP) • ‘Basic algorithm’, Strube and Hahn 1999 • Incremental algorithms: Strube, 1998; Tetreault, 1999, 2001 • Generation: • Text planning: Kibble and Power, 2000; Karamanis, 2001, 2002 • NP realization: Henschel, Cheng, and Poesio, 2000 • A number of evaluation studies: • Walker, 1989 (BFP vs. Hobbs) • Strube and Hahn, 1999 (SH vs. BFP) • Strube, 1998 (S-LIST vs BFP) • Tetreault, 2001 (History List vs. Hobbs vs. BFP vs S-LIST vs. LRC) LSA

43. Brennan et al (1987) • The first and, arguably, still best-known algorithm for pronoun resolution based on Centering was proposed by Brennan, Friedman and Pollard (1987) • Parameter configuration: • Utterances: sentences • Ranking: grammatical function • Realization: direct?? • Along the way, Brennan et al also developed the formalization of Centering which is best-know • E.g., the terminology of ‘Constraints’ and ‘Rules’, or the division of ‘Shifts’ into ‘Smooth shift’ and ‘Rough Shifts’ LSA

44. The algorithm • GENERATE possible Cb-Cf combinations (or anchors) • FILTER these anchors by constraints: • Binding theory, • sortal predicates • Centering rules and constraints • RANK the remaining anchors according to transition preferences: CONTINUE < RETAIN < SMOOTH-SHIFT < ROUGH-SHIFT LSA

45. An example (1) u1. Terry really goofs sometimes. (2) u2. Yesterday was a beautiful day and he was excited about trying out his new sailboat. (3) u3. He wanted Tony to join him on a sailing expedition. (4) u4. He called himat 6AM. (5) u5. He was sick and furious at being woken up so early. LSA

46. Analysis of the example (1) u1. Terry really goofs sometimes. CB = NIL CF = [Terry] (2) u2. Yesterday was a beautiful day and he was excited about trying out his new sailboat. Referring expressions = [yesterday, A1, A2, the sailboat] Possible CF lists: [yesterday, Terry, Terry, the sailboat] Anchors = a1. <Terry, [yesterday, Terry, Terry, the sailboat]> a2. <NIL, [yesterday, Terry, Terry, the sailboat]> Filter out a2. CB = Terry CF = [yesterday, Terry, Terry, the sailboat] transition = ESTABLISH / CONTINUE LSA

47. Example, cont’d (3) u3. He wanted Tony to join him on a sailing expedition. CB = Terry CF = [Terry, Tony, Terry, a sailing expedition] (4) u4. He called himat 6AM. Referring expressions = [A3, A4] Possible CF lists: [Terry, Terry] [Terry, Tony] [Tony, Terry] [Tony, Tony] Anchors = a1. <Terry, [Terry, Terry]> a2. <NIL, [Terry, Terry]> a3. <Tony, [Terry, Terry]> ….. Filter out all anchors except for <Terry, [Terry, Tony]> (CONTINUE) and <Terry, [Tony, Terry]> (RETAIN) CB = Terry CF = [Terry, Tony] transition = CONTINUE LSA

48. Example, end (5) u5. He was sick and furious at being woken up so early. Referring expressions: [A1] Possible CF lists: [Terry], [Tony] Possible anchors: <Terry, [Terry]> (CONTINUE) <Tony, [Tony]> (SMOOTH-SHIFT) CB = Terry CF = [Terry] LSA

49. A more complex example (1) u1. Susan gave Betsy a pet hamster. CB = NIL CF = [Susan, Betsy] (2) u2. She reminded her that such hamsters were quite shy. Referring expressions = [A1, A2, hamsters] Possible CF lists: [Susan, Betsy, hamsters], [Betsy, Susan, hamsters] Anchors = a1. <Susan, [Susan, Betsy]> a2. <Betsy, [Susan, Betsy]> a3. <NIL, [Susan, Betsy]> a4. <Susan, [Betsy, Susan]> a5. <Betsy, [Betsy, Susan]> a6. <NIL, [Betsy, Susan]> Filter out a2, a3, a5, a6. LSA

50. Kehler, 1997 (1) u1. Terry gets really angry sometimes. (2) u2. Yesterday was a beautiful day and he was excited about trying out his new sailboat. (3) u3. He wanted Tony to join him on a sailing expedition, and left him a message on his answering machine. (4) u4. Tony called him at 6AM the next morning. (RETAIN) (5) u5. He was furious for being woken up so early. He = Terry: CONTINUE. He = Tony: SMOOTH-SHIFT. (5’) u5. He was furious with him for being woken up so early. (CB = Tony) He = Tony, him = Terry: SMOOTH-SHIFT He = Terry, him = Tony: ROUGH-SHIFT (5’’) u5. He was furious with Tony for being woken up so early. (CB = Tony) He = Terry: violation of Rule 1 LSA