4.
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Summarv ReDort of Research Activities and
Results (Grant No. ROOO222647).
When we read a sentencewe first identify the words of the sentenceafter which we
computethe structural(syntactic)relationsbetweenthe words. Oncethe syntactic
structureof the sentenceandthe individual word meaningsareknown, it is possibleto
computethe meaningof the sentenceas a whole. Thematicprocessingis a
subprocessinvolved in the computationof the meaningof a sentence.Essentially,
thematicprocessinginvolves working out who or what did what to whom. Linguists
have long stressedthe importanceof thematicroles in the descriptionof linguistic
phenomena(Carlson, 1984;Gruber, 1965;Filhnore, 1968;Jackendoff,1972;
Chomsky, 1981;Bresnan,1982). Thematicroles suchasAgent, Instrument,
Location, Patientetc are linguistic constructsthat allow us to capturethe semantic
relationsbetweenevents,statesor objectsin a sentence.Psycholinguistshaveargued
that thematic roles may act as a link betweenthe syntacticand semanticcomponents
of language(e.g. Bock & Loebell, 1990;RaynerCarlson& Frazier, 1983). Consider
an example. A sentencecontainingthe verbput usually involves an entity moving a
particular object to a particular location. In the sentenceTheboyput the mug on the
table, the entity performing the action,the Agent, is the-boy. The object being put,
the Patient, is the mug andthe Location is the table. Eachverb hasa thematicgrid in
which all the thematicroles associatedwith it are stored. For example,the verbput
hasa thematic grid with threethematicroles in it. Thus, thejob of the thematic
processorduring languagecomprehensionis to computewhich entitiesmentionedin
the sentenceare assignedto which thematicroles. It is in this way that the thematic
processoractsas a bridge betweenthe syntacticprocessor(concernedsimply with
constructingthe structuralrelationships)betweenwords andthe semanticprocessor
(concernedwith computationof the overall meaningof a sentence).
In a recent article, Liversedge,Pickering, Braniganand Van Gompel,(1998) reported
two eye movementstudiesthat investigatedthe psychologicalreality of thematic
roles. In particular, they were interestedto know whether wh-words(e.g. where or
who) inpreceding sentencesaffectedhow peopleprocessa subsequentsentencethat
is thematically ambiguous. Liversedgeet al usedsentenceslike 1.and 2.
la. The head gardenerdecidedwhereto plant the shrubs.
lb. The headgardenerdecidedwho shouldplant the shrubs.
2a.,In fact the shrubswere plantedby the greenhouse.
2b. In fact the shrubswere plantedby the apprentice.
The target sentencesin (2a) and (2b) contain a by-phrasethat is ambiguousbetweena
Location (by the greenhouse)and an Agent (by the apprentice). Liversedgeet al
showedthat precedingcontext affectedthe easewith which readersprocessedthe
ambiguousby-phrasein the target sentence.
In the first two experimentsin our proposalwe attemptedto extendthesefindings to
adjunct ambiguitiesusing sentenceslike 3a and 3b.
3a. The maid thought aboutwhen to prepare/whereto prepare/preparingthe
vegetables.
3b. In fact shepreparedthe vegetablesin the morning/kitchen,and cookedthe meat
aswell.
We measuredreadingtimes for suchsentencesin an eyetracking experiment.
However, therewere no reliable differencesin readingtimes for the early experiments
(despiteearlier sentencecompletionstudiesindicating that the materialsdid induce
the appropriatethematic expectations).We thereforemodified our material set to
removeany extraneouslinguistic information to ensurethat subtlethematiceffects
were not being swamped. We testedthe new material setin anothereyetracking
experimentand this time found reliable readingtime differences. Participantstook
longer to readthe target sentenceswhenthey were precededwith a thematically
incongruouscontext sentencethan when they were precededby a thematically
congruouscontext sentence.
Finally, we developeda secondstrandof researchthat we conductedin parallel to the
main ongoing vein of thematicresearch.Collaborativelinks with Dr Kevin Paterson
at the University of Derby led to an experimentinvestigatingfocusoperators.
Paterson,Liversedge& Underwood,(1998) showedthat, contraryto the claims of Ni,
Crain and Shankweiler,(1996),the focus operatoronly doesnot guideparsingof
reducedrelative clausesentences(like 4a and 4b) with a noun phrase,verb, noun
phrasestructure.
4a. The teenagersallowed a party invited a juggler straightaway.
4b. Only teenagersallowed a party invited a juggler straightaway.
we arguedthat this is becausethe thematicprocessorhasa very strongpreferenceto
assignan Agent role to the first noun phraseof the sentenceand a Patientrole to the
second. We thereforeran a secondexperimentusing sentenceslike 5a and 5b in
which a prepositionalphraseimmediatelyfollowed the ambiguousverb thereby
blocking the strongly preferredthematicassignment.
5a. The soldiersattackedin the night capturedmany prisoners.
5b. Only soldiersattackedin the night capturedmany prisoners.
We hypothesisedthat sincethe stronglythe preferredreadingwas ruled out due to the
presenceof the prepositionalphrase,then the focus operatormay exertmore of an
influence over the initial syntacticanalysisassignedto the sentence.Indeed,when we
examinedreadingtimes for thesesentenceswe found that subjectsexperienced
difficulty reading sentenceslike 5a,but did not when they read sentenceslike 5b. We
concludedthat the focus operatorcaninfluenceinitial parsingdecisionsfor some
structures‘for which there is not a stronglypreferredinitial syntacticanalysis(for a
full accountof this experimentseeClayes,Liversedge& Paterson,2000).
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