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<?xml version="1.0" standalone="yes"?> <Paper uid="J79-1027"> <Title>American Journal of Computational Linguistics Mi crof i C~Q 2 7 A FORMAL PSYCHOLINGUISTIC MODEL OF SENTENCE COMPREHENSION</Title> <Section position="8" start_page="30" end_page="30" type="concl"> <SectionTitle> JJ </SectionTitle> <Paragraph position="0"> a link Ui=Vj (whsre Vj occupies the same argument-place in B~~ as does vf J in the predicate B of the pattern) 1 for ui to match a description Ajvj, there must be an expression Ajui in the ISR.</Paragraph> <Paragraph position="1"> For instance, pqlr earlier example (20) r (20) This bread was sold to John by the Italian baker. contains the constituents BRW, JOrIN, BAKER, and SELL8 They are linked in accordance with the pattern (21), which stated fhat bakers typically sell baked goods to people. 3ere BR~Av in (20) matches (by implicatfon) BAKE~GOOD in (21), BAKER in (20) matches BAKZR Ln (21), JWN matches HUMAN, Bnd SW matches SELL. iiecall that the Intersection Strategy in (19) debmines just which patterns are called up far a giben sentence. Th~re will usually only be a limited number of activated patterns, Next consider the Contradiction ~limination Strategy.</Paragraph> <Paragraph position="2"> An abbreviated verEIion of it is aiven in (29) Roughly, the rule %ests which roles each NP could play without leading to a contradicption, Then it checks whether this would lead to a unique combined role assignment for all noun phrases, and if so, it accepts this combination as the interpretation. (29) Contratiiction Elimination Strateevr (1) Let vlaSav be prefix head-variablea of a single rn type T, and ul...u WB-arguments of the same type TI n (23 add each combinatorily possible non-contradictory link Vito a list: if there is a uniaue combinead m-tuple of lank8 vl=ud & . & v,=uk (where no ui or vi OCCUF~ more than once), then add this m-tuple of ZLnks to the SR.</Paragraph> <Paragraph position="3"> An example is shown in (30)' Notice that even though mouse, taken by itself, corrld be either logfcal subject or object of see, the combination mouse/cheese has a unique semantic relation to see, because cheese can of course only be logical object of see. The ~an~nicai Order Stratem is shown in (31). iioughly, the strategy attempts to equate the surface order of the major clause oonatituents with 'their &quot;deep order I I (31) Canonical Order Stratenar (1) Let vl, .a,v rn (m>l) be prefix headvariables of a single type T (where Vi precedes vj; for i< j(m) , and let ul,e.~,u, be type T argument places of MVB (where ui precedes u for i<j~n) 8 (2) then each Vi not yet linked to any matru-constituent is linked to the MVB-argument ui, unless MVB has the feature PASV in the syntactic structure.</Paragraph> <Paragraph position="4"> Far example, let (33) be the preliminary SR of (32): (32) John gave the cat some milk.</Paragraph> <Paragraph position="5"> Here the first three prefixes are not yet linked to any matrix-constituent, and their head-yariablee &, y, p, are of the same type. Hence they are linked as in (34), yielding, after simplification, the find SR (35).</Paragraph> <Paragraph position="6"> Finally, 3 describes the svntax-sensitive rule. It is seneuive to the fdature 3?Aw of the verb and links the constituents marked S7Mr OBJl, 0BJ2, and AGenT to the main verb, insofar as this has not been done by earlier strategies. (36) Wtu-sensit-ive NNB-rRulet (1) 2he first MVB-argument is linked to the prefix head~&t?ia5le pointlng to: {a) the SW-phrase if MVB is not marked PASV; (b) the AGT-phrase if there is such a phrase: (2) link the - prefix head-variable pointing to 8 (a) an ORTI-phrase to the second MVB-argument1 (b) an OBJ2-phrase to the third WB-argument; (3) if MVB is PASV Unk the prefix head-variable pointing to the SBJ-phrase to the remaining free (but not the f irst-) MVB-argument.</Paragraph> <Paragraph position="7"> An example is given in (37)d~ere as elswhere in this paper, &quot;#&quot; atande for initial and &quot;$&quot; for final clause boundary.) (37) # The churchSBJ had been givenPASv the moneyow2 $ L#Pos~c~] by the bakerACT $a</Paragraph> <Paragraph position="9"> Links; x pdints to OBJ2. hence x=zg; y pomt.8 to S0J of a PASV verb, hence</Paragraph> <Paragraph position="11"> Linkr z points to AGT-phrase, hence z=zl by option (lb)i VXII a DIFFEi3ENT XOD3S OF PROCESSING Let me interrupt here to consider the practical problem of constructing an automatic sentence recognizer. Some aspects of the thapry I have just sketched may not be optimal for a ~omputational model, even though they seem appropriate for a psychological model. For instance, to a pefson engaged in normal conversation accuracy of understanding is not very crucial most of the time&quot; Often, the goal may only be to '-get the essentials,&quot; and if some mistake &s made, it is simply corrected later on.</Paragraph> <Paragraph position="12"> This &quot;normal mode of processingw is what the psychological model sets out to describe. Now, in the case of an artificial intelli~rtnce system, one would probably demand higher accuracy, so as to minimize the need for correctionsm This is, in some ways* similar to the situation where you put subjects in a psychulinguistic experiment. They usually abandon the &quot;normal mode of processingw very soon and instead employ the strategies that guarantee best performance for the specific experimental task they are faced with . To give an example, consider the common type of experiment where a subject has to verify sentences like those in 138).</Paragraph> <Paragraph position="13"> (38a) 5 precedes 13.</Paragraph> <Paragraph position="14"> (38b) 5 is preceded by 13.</Paragraph> <Paragraph position="15"> (384 13 is preceded by 5.</Paragraph> <Paragraph position="16"> In order to interpret such sentences correctly, his knowledge that 5 in fact precedes 13 is of no help whatsoever to the listener, because true sentences occuf together with false ones in this game. Therefore, he will soon drop all semantic short cuts --which he normally eaploys-- and interpret the sentences purely on the basis of their syntax. In a way, therefore, such experiments do not really tell us anything about normal speech processing.</Paragraph> <Paragraph position="17"> Still, such conditions o'f heightened aecuracy may be just the onee we want to apply to the artificial intelligence system. Let us therefore consider how such a non-normal mode of processing could be sinulated in our theory.</Paragraph> <Paragraph position="18"> Now, looking back at the Linking Strategies in (22) above (~lnking by Variable Type, Pattern latching, Contradictinn-Xlimination, Canonical Order, ana Syntax-sensitive MVB-~ule), there is indeed ar. obvious way of simulating the &quot;high accuracy procedure,&quot; namely by dropping type 2, 3, and 4 strategies. 'Phese coflstitute the &quot;shore cuts&quot; which work 90% of the time, but sometimes lead to misinterpretations. Notice that the result is still not a syntax-governed model, because most of the linking would still be handled by the syntax-free ne'chod of Linking4by Variable Type, and syntactic btruc tare ~ould still be erased in clause-intervals, As a matter of fact, in this last respect I think it is possible to go even further than I have done here, and erase syntactic structure after each major clause constituent (i.e., after each NP, adverb, or main verb), retaining only its functional feature, which is then simply integrated into the semantic representatbn. I have already done this here for the constituent ~ain~er~, so in a way this woula only be a logical extension of my proposal Looking at the syntax-sensitive MVB-Rule (36) , it is evident that it rerers exactly to those functional features, namely SBJ, OBJ1, OBJ2, MVB, and AGT.</Paragraph> <Paragraph position="19"> It would seem, then, that even for purposes of artific'ial in%lligence, it may be preferable to operate with a parallel processing model, thereby minimizing the size of the syntactic gltructl~re and the amount of syntactic operations.</Paragraph> <Paragraph position="20"> Apart from this, I would like to argue that the essential ingredients. of Pattern Matching and Contradiction-Elimination are still required for any adequaze tJleo~. Ws-bri~g back to the sixth type of Semantic Linking Strategies, namely Alternative Linking Strategies.</Paragraph> <Paragraph position="21"> IXsWALTERNATNE LINKING STRATEGIES&quot; Alternative Linking Strategies apply if the normal strategies (types 1-51 have failed to produce a semantically acceptable reading. These strategies rely heavily on the Semantic Knowledge Rules.</Paragraph> <Paragraph position="22"> The most important and most general (and the only one to be discussed in the present paper) is the Obvious Connection Strategy in (39). It says, roughly, that if a variable g cannot be linked to the RnB then if the encyclopedia contains a rule conne~ting q to same other entity 11' then try and link this new entity yo to the MVB.</Paragraph> <Paragraph position="23"> If the head-variable u cd a prefix (QTF~UIAU) cannot be lhked to its appropriate IWB-argument V, and both u and v point to a rule in the encyclopedia such that a connection (~~~~u't~u')[~uu'~between u and u' is derivable, then t (a) qhange (QTF~UIP-~) to <QTF~U'Z(QTF~U~AU)(BU~ & CUU')), (b) link ut to v.</Paragraph> <Paragraph position="24"> For Instance, consider again sentence (9b)l (9b) They published Wodehouae immediatela he came over.</Paragraph> <Paragraph position="25"> s indicated in (40), the object of PUBLISH must be some ritten work, and Wodehoyse of course does not qualify as uch. Therefore, the l5nR between x odeho house) and the ogical object ye of PUBL~~H is rejected. Notice that this s just the kind of &quot;semantic anomaly test&quot; which was central o the Contradiction-Elimifiation Strategy Its intuitive asis is obviousr the listener normally assumes that the peaker is trying to make sknse, and therefore, he will eject all non-sensical interpretations.</Paragraph> <Paragraph position="26"> Now, staying with our sentenae (40) hey published h ode house), if you know that Wodehouse was a writer you also know that he created written works3 and ths new entity introduced by this encyclopedic rule, namely &quot;written works created by Wodeh~use,~ is the one which is interpreted as .logical object of the predicate PUBLISH. This then is the kind ofWsernantic detourw descrttJeb by tRe ObvTous ConnectLon strategy, and this strategy is applicable to the other sentences in (9) too Now, I think the sentences in (9) exemplify something that happens all the time in speech: namely omission of the obvious. I also think it would be extremely inconvenient if we had to ask people to use only their best Sunday Grammar when conversing with an English-speaking robot. Me might as well ask them not to use pronouns, or to speak at a constant pitch of 4.00 Hertz. To be competitive, the robot should undecstand Monday Gramar as well, and that means, sentences</Paragraph> <Paragraph position="28"> For the remainder, 3: would like to discuss clause-to-clause 1Mcing. The dieti~lguishing feature of my proposal, as will See ~chank(1972) for a different approach to the problem of recovering implicit information. He outlines, for instance, a method by which &quot;I like books&quot; would be expanded into the conceptual equivalent of &quot;I like to read books.&quot; SchankDs theory is baqed on wconceptual casesw and lexical decomposition rather than meaning postulates. For instance, he claims that &quot;John would be pleased by Il:ary8s going&quot; is a proper part of the meanhg of John wants Marv to come home, while in my terms &quot;John would be pleased by !daryw s going&quot; is merely an allowable inference which may or may not be drawn. Failure to Eraw an allowable inference explains the possibility of holding contradictory beliefs . For instance, somebody might judge John's uncle left to be true, while at the same time believing that the brother of John's mother or father left was false, because he failed to apply the mean%% rule relating uncle and brother of mother or father.</Paragraph> <Paragraph position="29"> It is difficult to see how a theory basedon lexical decomposition would explain such f&c ts Certainly , it would be unreasonable to claim that a person has not understood the sentence John's uncleJaft unless he also is aware of the synonymy relation between this sentence and the brother of John's mother or father Left be recalled, is that syntactic structure is erased clause-byclause. The problem, therefore, is to show that sentences containing more than one clause can in fact be interpreted correctly without referring to the full syntactic structure of any (completed) earlier clause.</Paragraph> <Paragraph position="30"> Consider first wPost-clauses&quot; e, clause-final adverbs, temporal nouns, and preposition-phrases Tliey are already covered by the strategy of Linkillg by Variable Type discussed earlier. For instance, consider again sentence (25a). (yesterday the father of tne boy sang horribly in the bath.) It contains the two P08-b-clauses horribly and in the bath; and it was shown earlier how they are linked to the main clalase by Variable Type The only smtac tic information required for this operation was the marking of the MVB in the semantic representation* (41) indicates roughly how relative clauses are integrated.</Paragraph> <Paragraph position="31"> (~ctuall~, there are some complications here, but they are irrelevant to the present discussion; the main point here is that again no reference need be made to the syntactic strracture of the first clause. For details, see ~eimold (f orthcomina where coordinate clauqes, comp&rison-clauses, and various sl~bjectleos complement-clauses are treated as well.) (41) # The girl (if who was tired 3) giggled q.</Paragraph> <Paragraph position="32"> (TMEX:GIRLX)[--~ and (~y) [T1i(E~yl link, y-xj integrated structure a (T~IEX I GIRLX & TIi-iEDx) C -- 7 Next consider circumstantial clairses like because the kan~aroo ium~ed in (43). The strategy for these claus~s, stat-ed in (42), does again not refer to the syntactic structure of the first clause* (42) Circumstantial - Clause Ruler Substitute the matria of the main clause for the free s-argument of the JUNCtor of the circumstantial clause, and join the prefix of the main clause before the prefix of the circumstantial clat~se.</Paragraph> <Paragraph position="33"> (43) # The boy wap nappy $(# lbecause JUNCJ the kangaroo jumped$)</Paragraph> <Paragraph position="35"> The same holds true for complement-clauses like that the cake was ~oisoned in (45). The corresponding strategy is given in (44).</Paragraph> <Paragraph position="36"> In sum, the principle of clause-by-clause erasure of syntactic structure seems ihdeed compatible with the requirements of clause-to-clause lirling. The exception is the feature MVB, and it was suggested earlier that this syntactic feature is integrated into the semantic representation Notice also that certain aspects of syntactic structure are reboverable from our semantic representations. For instance, the order of the prefixes in the SR reflects the surface order of the NP'a of a clause. Hence, if certain constructions require access to such syntactic aspects, this i8 still not incompatible with erasure of syntactic structure in clause intervals. or instance, coordinate clauses and certain subjectless complement clauses do often require identification of the surface subject. For detailed discussion, see</Paragraph> <Paragraph position="38"> The last strategy discussed here concerns the tense of consecutive clauses. When we interpret sentences S1, 52 in a text or sentence conjunct, where S3, and S2 have the same tense, we often assign a relative chrondlogy to the events described by these sentences. I will refer to the principle assigning such a chronology as the Temporal Sequence Strategy.</Paragraph> <Paragraph position="39"> For example, consider (46) (Agatha Christie, Thev came to Baghdad, pmlOO)t (46) Then his head jerkedtl back a little and he lay still.</Paragraph> <Paragraph position="40"> Assigning PAST(^^) to the first clause and PAST(^^) to the conjoined clause in (46) does not account for actual comprehension: the listener knows that t2 is later than tl, even though there is no overt sequewe marker (e sg*, before, after, then) As a first approximation, the strategy might be stated as f 011 ows t (47 ) Tem~oral Sequence stratem (preliminary) I Given two main or conjoined clauses C1, C2 such that C1 precedes C2 and the time tl of C1 has the same &quot;tense predicatew (e.g., PAST, FUTURE) as the time t2 of C2, then assume that DIRFRBC tp= (47) will require several modifications . First, the rule holds for certain nan-tensed clauses as well, as illustrated by (48) (~hesr came- to Baghdad p 044) 8 (48) Then he was out, across the Khan, back into the Suq. . The full interpretation of (48) must specify that the time of out precedes that of acrcws, which in turn precedes that of bacq. Since across and back had no overt tense predicate in i48), the strategy must somehow be Liberalized to include SUC~ C~S~S.</Paragraph> <Paragraph position="41"> In this connection, consider also (49)(~hey came to Baghdad. pa711 1 (49) Never. I thought, would the plane land. It went round and round*:! and roilndt,.</Paragraph> <Paragraph position="42"> t 1 If we assumed that tpt2=t3 in (49), then the two conjoined phrases pnd round and round* should be redundant in the same sense in which Fido ia a dog and is a doe: and is a dog is. However, (49) can quite naturally be interpreted as &quot;the plane went-round and then round and then roundN be.. as 45. -DIRPREC t2 & _t3 DIRPREC t3).</Paragraph> <Paragraph position="43"> Next, the Temporal Sequence Strategy seems blocked if some general semantic principles \in ~articular, Pattern Matching) suggest a chronology caR#licting with that imposed by the Temporal Sequence Strategy. For instance, consider a dialogue like (50): (50a) What's the matter with John? (50b\ Oh, he broketl his arm. He felltZ off his bike. Here the second sentence in (sob) is interpreted as preceding the first sentence in (50b) temporally, counter to what the Temporal Sequence Strategy would prediict. The reason is obviousr there is a perceived causal connection between the sentences, such that the second sentence describes the cause of the first. Since a cause must precede its effect, t2 must precede tl in (50b).</Paragraph> <Paragraph position="44"> To formalize this, we can make use of Pattern ittcbing. For instance, the encyclopedia would contain a pattern like (51), and there would furthermore be a meaning rule like (52). (52) (AU.,tl,t2) LCAUSE<A(. dl. a) ,B(. at2. 43 IMPL tl CIRPREC t2 3 We need only make sure that the pattern (51) is activated by the two sentences he broke his arm and he fell off his bike in (~oB), which can be- done by calling up all patterns which are in the intersection of the main verbs of the two sentences. pa or instance, break and fell both point to (51).) In effect, we have to add the following principle to the Temporal Sequence of C1 and C2. If 4 DIRPREC tl is heuristically derivable from a pattern, then add this link tu C2 and do not apply the Temporal Sequence Strategy.</Paragraph> <Paragraph position="45"> Another restriction seems to be that the Temporal Sequence Strategy is inapplicable to proaessive tense. For instance, while tl must precede t, in (54), they seem to be roughly simi~ltaneous in (59, even though liatina a ci~mette and leaving a room normally count as &quot;instantaneous&quot; events (see The condition against conjunction by and is necessary since pnd can never mean &quot;and before that..,&quot; For instance, a sentence like pe broke his arm and fell off his bike. cannot be interpreted as &quot;he broke his arm because he fell off his bike. tB progressive tense turns events into non-instantaneous events.</Paragraph> <Paragraph position="46"> Finally, I come to EUhe most general and important restriction on the Temporal Sequence Strategy, Phis restriction is of a subtle semantic nature: it states that the strategy is applicable to clauses C1, C2 on1~ if the events described by C1 and C2 are unlikely to he simultaneous. Consider, fqr instance, the following sentence: (56) She just stood there and looked at him.</Paragraph> <Paragraph position="47"> It is perfectly possible for someone to stand somewhere and at the same time to look at somebody. Hence no temporal sequence is imoosed on stood and looked. By contrast, in (57) (~heu came to Baghdad, p.76) wen3 and stood must be interpreted as seqyenced, since one .cannot at the same time a somewhere and stand somewhere elser (57) She wenttl out from the bar onto the terrace outside and stood% by the railing...</Paragraph> <Paragraph position="48"> Note that it will not do to define.the condition of &quot;possible simultaneity' directly for verbs. We cannot say, e.g., that clauses containing stand and a must be&quot;sequencad.&quot; For instance, in (58) and (5% stood and went would be interpreted as simultaneous, the reason being, of course, that different agents are involved, which makes simultanei-ty c onc e ivabl e .</Paragraph> <Paragraph position="49"> (58) Jack stood by the window. Jane went to the door. (-59) Jane went to the door. Jack stood by the window. It is clear, then, that a detailed semantic analysis is need6d to determine &quot;possible simultaneity of two events. The principle can be stated as follows: (60) possible Simultaneitv Constraint: Call u~ allEncyclopedic Rules in the intersection of the MVBms of. C1 and C2. Unless tl t2 is derivable (stricrtly or heuristically) the Temporal Sequence Strategy is inapplicable There are some cases, however, where two events are nocmally ihterpreted as sequenced, even though they could, stric-tly speaking, be sirnultaneous~ For instance, it is theoretically possible to light a cigarette while g&tting up, and one certainly would not want to add a rule to the encyclopedia stating that two such events are unlikely to be' sinnaltaneo~s~ Nonetheless, (61) is normally interpreted a8 sequences I (61) John got up and lit a cigarette.</Paragraph> <Paragraph position="50"> Aather than adding some ad hoc principle whlch somehow codes the intuition that it is awkward to strike a match and hold it to the cigarette while geteing up, we can exnlain this as a consequence of a much more general heuristic principle. Notide that both clauses of ( 61 ) describe instantaneous events. Now, the shorter tdo events, the lower the probability that they coincidel For instance, the probability that the radio plays at the same time when there is a- shot is duch higher than the probability of there being a shot at the same time wi~h a hiccough. As another illustration. consider (62)(~hev came to Baadad, p. 72): (62) With a fatherly smile he withdrewel, Victoria sat down, on the Ded and passed, an experimental hand over her hair. Although it is Legically conceivable that all three events el-e3 happened simultaneous~y, the normaL in~erpretation of these sentences takes them to be sequenced, because they are short and henca unlikely to coincide.</Paragraph> <Paragraph position="51"> This means, then, that we must add the following heuristic principlm t If C1, C2 denote $nst$uvt@neous events e, JNSTANT tl and STA ANT t2 are derivable from M-rules and E-rules) assume that tl#t2.</Paragraph> <Paragraph position="52"> In summary, the Tem:poporal Sequence-Strategy takes on the followinq form: (64) Tem~oral Seauenee ~trate~v(revised)t (1) Let C1, C2 be two main or conjoined clauses such that CL is to the left of C2 and the time tl of the MVB of C1 has the same tense predicate as the time t2 of the MVB of C2, or t2 or both tl and t2 have no tense predicate; and neither tl nor t2 has the tense predicate PROGRESSIVE; (2) call up all Encyclopedia Rules in the intersection of the WB of C1 and the WB of C2; (a) if C2 is not introduced by and, and 2 DIRPREG tl is heuristically derivable from the active E-rules and i-rules, then add 42 DLSPREC ti and break off the application of this strategy; (b) if ei'ther - tl= or INSTANT t~& it? dderi-e (strictly or heuristically) from the active E-rules and M-rules, then add the link DIRPRZC t9.</Paragraph> </Section> class="xml-element"></Paper>