Do verb bias effects on sentence production re ect ...

Do verb bias effects on sentence production reflectsensitivity to comprehension or production factors?

Victor S. Ferreira and Elizabeth R. SchotterDepartment of Psychology and Center for Research in Language, University of California, San Diego,La Jolla, CA, USA

Speakers should be motivated to produce easy-to-understand sentences, but they must successfully saysentences that are harder to produce. Four experiments assessed how verb bias influences the mention ofthe optional “that” in sentence-complement structures. Without the “that”, such sentences can be incor-rectly interpreted as including direct objects (garden paths), and especially so after direct-object-biasedverbs (compared to embedded-clause-biased verbs). But direct-object-biased verbs are rarely producedas sentence-complement structures, and so they might be harder to produce as such. Experiments 1and 2 show that speakers mention the “that” more after direct-object-biased verbs than afterembedded-clause-biased verbs. Experiment 3a shows that sentences with verbs biased toward neitherdirect objects nor embedded subjects were often produced with the “that”, and Experiment 3b showsthat postverbal noun phrases after neither-biased verbs are interpreted as direct objects less thandirect-object-biased verbs and so should cause a milder garden path. Thus, frequent “that” mentionis not sensitive to the tendency of a verb to be followed by a direct object, but by how rarely the verbhas been produced in the formulated structure.

Keywords: Language production; Communication; Ambiguity; Frequency.

Speakers speak to be understood. Presumably, theeasier a sentence is to understand, the more likelyit is that it will be understood successfully. So,given a choice and all else equal, speakers shouldproduce sentences that will be easier for theiraddressees to understand.

But all else is not always equal. The mechanismsresponsible for language production, like the mech-anisms responsible for any behaviour, are subject to

cognitive demands. One powerful demand is effort:Some behaviours are easier to perform than others.And so speakers might produce particular sentencechoices rather than others not in service of any goalto be better understood, but instead to perform aneasier rather than a harder behaviour.

Consider a sentence like “The talentedphotographer accepted (that) the money couldnot be spent”. Sentences like these, termed

Correspondence should be addressed to Victor S. Ferreira, Department of Psychology, University of California, San Diego, 9500Gilman Drive, La Jolla, CA 92093-0109, USA. E-mail: [email protected]

The research reported in this manuscript was supported by NIH (National Institutes of Health) R01 Grant HD051030. Thanks toKatie Doyle, Carla Firato, Michelle Groisman, and Allison Peters for assistance with data collection and analysis, Susan Garnsey forher generosity with materials and advice, and Florian Jaeger and the members of the Language Production Laboratory at UCSD(University of California, San Diego) for discussion.

# 2013 The Experimental Psychology Society 1

THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2013http://dx.doi.org/10.1080/17470218.2012.753924

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sentence-complement structures, are grammaticalwhether speakers mention or omit the “that”(termed a complementizer). Furthermore, the pres-ence or absence of the “that” has little (Bolinger,1972; Thompson & Mulac, 1991; Yaguchi, 2001)or no effect on the overall meaning of the sentence.But, research suggests that the mention or omissionof the “that” can have other effects. One such effectis about understandability: The “that” can makesome sentences easier to understand. Anothersuch effect is about cognitive demands: The“that” can accompany sentences that are harder toproduce. Each of these is discussed in turn.

Garden-path sentences

Consider the sentence beginning, “The talentedphotographer accepted the money . . . ”. At thispoint in the sentence, a comprehender is verylikely to interpret the noun phrase “the money” asa direct object, as in a sentence like “The talentedphotographer accepted the money gleefully”. Thisis because at this intermediate point in thesentence, the interpretation where “the money” isa direct object is simpler (F. Ferreira &Henderson, 1990) and more common (Trueswell,Tanenhaus, & Kello, 1993), and so comprehendersare likely to interpret the sentence that way. But inthe actual sentence, “the money” is not a directobject; it is the subject of the embedded clause “themoney could not be spent yet”. This means thatupon comprehending “could”, the comprehendermust revise his or her original interpretation sothat “the money” is understood to be an embeddedsubject—the subject of an embedded clause.

This processing sequence whereby a compre-hender initially interprets a sentence incorrectlyand then revises it is termed a garden path.Garden paths represent the difficulties that com-prehenders experience as they understand sen-tences, and, as a result, they have been heavilystudied in the psycholinguistic literature (becausethe kinds of garden paths comprehenders are vul-nerable to and how they overcome them revealsthe nature of the mechanisms responsible for sen-tence comprehension). Because garden paths posedifficulties for comprehenders, speakers who want

to be understood might avoid producing them.Indeed, in sentence-complement structures, this iseasily done: If a speaker mentions the optional“that”, the garden path is eliminated (“The talentedphotographer accepted that the money . . . ” cannotbe interpreted with “the money” as a direct object).So this raises the interesting possibility that speak-ers might mention the “that” specifically in sen-tences that would otherwise cause especiallydifficult garden paths.

The current research examines how verb biasesinfluence speakers’ sentence-production choices,specifically whether speakers mention the “that”or not in sentence-complement structures. Here,verb bias refers to how frequently the main verbin a sentence-complement structure is generallyproduced in sentence-complement structures—that is, followed by an embedded clause—versusas a simple transitive sentence—that is, followedby a direct object. Main verbs that are frequentlyfollowed by embedded clauses and rarely followedby direct objects are termed embedded-clause-biasedverbs, and main verbs that are frequently followedby direct objects and rarely followed by embeddedclauses are termed direct-object-biased verbs.(Although we describe verb bias as though it is acategorical factor, verbs’ biases can in fact vary con-tinuously. That is, a verb may rarely, sometimes, oroften take an embedded clause, or it may rarely,sometimes, or often take a direct object. Analysesbelow consider verb bias categorically, as well ascontinuously, defined as how often a particularverb is followed by a direct object divided by thesum of how often it is followed by a direct objectplus embedded subject.) Important here is thatthe bias of the main verb in a sentence-complementstructure affects how severely the garden pathwithin that structure disrupts comprehension.Specifically, Garnsey, Pearlmutter, Myers, andLotocky (1997) showed that sentence-complementstructures with direct-object-biased main verbsgenerally caused bigger garden-path effects thansentence-complement structures with embedded-clause-biased main verbs. This difference arisesbecause direct-object-biased main verbs morestrongly encourage comprehenders to interpretthe noun phrases following them incorrectly as

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FERREIRA AND SCHOTTER

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direct objects—they usually are. But of course, insentence-complement structures, these nounphrases are embedded subjects. Meanwhile,embedded-clause-biased main verbs less stronglyencourage comprehenders to interpret the nounphrases following them as direct objects, insteadencouraging the ultimately correct embedded-subject interpretation.

Intriguingly, there is evidence showing that inaccordance with this comprehension difference,speakers are more likely to produce the garden-path-eliminating “that” in sentence-complementstructures with direct-object-biased main verbsthan in sentence-complement structures withembedded-clause-biased main verbs. Garnseyet al. (1997) normed the verbs they used to deter-mine their biases. To do so, they asked a group ofsubjects to complete sentence onsets of the form“Karen accepted __________” and measured howfrequently writers completed the sentences withembedded clauses, direct objects, or some otherstructure. Of course, when writers completedonsets with embedded clauses, they either includedor omitted the “that”. Although not directly rel-evant to Garnsey et al.’s main point, they reportedhow often subjects included the “that” with anembedded clause completion in sentences withembedded-clause versus direct-object-biasedverbs. They found a difference: Writers’ sentence-complement completions with direct-object-biased main verbs included the “that” more thantheir sentence-complement completions withembedded-clause-biased main verbs. This differ-ence is intriguing because it might show thatlanguage production mechanisms in fact choosesentence structures that are easier to understand,in that they insert the “that” more just in thosestructures that would otherwise be harder to under-stand. (It is worth noting that the garden pathunder scrutiny here is relatively mild, so the gainsachieved by avoiding them may not be great. Butthe question here is, given that there is a differencebetween verbs with different direct-object vs.embedded-clause biases, is it due to the disruptive-ness of the garden path elicited by such structures?)

An implementation of a production strategywhereby speakers mention the “that” to avoid

especially disruptive garden paths might begin byhaving verbs in speakers’ production lexiconsencode the likelihood that they continue withdifferent arguments. A verb here classified asdirect-object biased may encode in the productionlexicon that it takes a direct object, say, 75% ofthe time and an embedded clause 10% of thetime. This information could then be used toguide the choice to mention the “that”; thegreater the direct-object likelihood relative to theembedded-clause likelihood, the more that pro-duction mechanisms will be biased to mentionthe “that”. Such a mechanism could be seen as aproduction version of an aspect of the constraint-satisfaction model of sentence comprehensionpresented by McRae, Spivey-Knowlton, andTanenhaus (1998).

Production effort

Producing a sentence is cognitively demanding. Itrequires speakers to conceive of a message, choosewords that can convey that message, construct asyntactic form that grammatically organizes thosewords and conveys relational information, retrievethe sounds of the ordered words, and then articu-late those sounds with an appropriate prosody, allat the same time. Naturally, the extent of thesedemands varies; conveying some messages canrequire harder to produce sentences than do others.

Evidence suggests that when producing sen-tence-complement structures specifically, speakersmention the optional “that” more in relatively diffi-cult-to-produce sentences. This has been shownmostly through manipulations of the difficulty ofretrieving sentence content. V. S. Ferreira andDell (2000) had speakers produce sentence-comp-lement structures from memory where theembedded subject did or did not repeat the mainsubject (e.g., “I knew (that) I . . .” vs. “I knew(that) you . . .”). Embedded subjects that are notrepeated should be harder to retrieve thanembedded subjects that are repeated.Correspondingly, V. S. Ferreira and Dell foundthat speakers said the “that” more in sentence-complement structures with embedded subjectsthat did not repeat main subjects than in those

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VERB BIAS EFFECTS ON SENTENCE PRODUCTION

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that did. Similarly, Jaeger (2010) found that in anatural speech corpus, embedded subjects thatreferred to the same referent as main subjectswere preceded by “that” less. V. S. Ferreira andFirato (2002) had speakers produce sentence-complement structures where the embeddedsubject was conceptually similar to or conceptuallydistinct from three noun phrases in the mainsubject (e.g., “The author, the poet, and the biogra-pher felt (that) thewriter . . . ” vs. “ . . . felt (that) thegolfer . . . ”). Conceptually similar embedded sub-jects should be subject to proactive interference,whereby retrieval is hindered by a type of simi-larity-driven confusion (Keppel & Underwood,1962). Correspondingly, V. S. Ferreira and Firatoshowed that speakers mentioned the “that” morein sentences with the conceptually similarembedded subjects. Furthermore, sentences withconceptually similar embedded subjects were pro-duced with more disfluencies (fillers like “uh” and“um”, etc.) than sentences with conceptually dis-similar embedded subjects, and sentences withmore disfluencies were produced more with the“that” (see also Jaeger, 2005, 2010). V. S. Ferreiraand Hudson (2011) had speakers produce sen-tence-complement structures as answers to ques-tions. To answer the questions, speakers had toadopt either their own perspective on a situationor their addressees’ perspective. Speakers shouldfind it harder to adopt their addressees’ perspectivethan their own, and, accordingly, V. S. Ferreira andHudson found that speakers mentioned the “that”more in answers requiring them to adopt theiraddressees’ perspective (see also Jaeger, 2010, forconverging corpus evidence). In sum, a range ofevidence suggests that speakers include the optional“that” more when producing more difficult-to-produce sentences.

The verb bias variable introduced above is likelyto determine in part the difficulty of producing sen-tence-complement structures. Verb bias reflectshow frequently speakers have produced particularmain verbs as particular structures. If a verb is fre-quently produced as the main verb of a sentence-complement structure, it may be easier to producethat sentence than if a verb is rarely produced asthe main verb of a sentence-complement structure.

Because direct-object-biased verbs are less fre-quently produced as the main verbs of sentence-complement structures, they may be more difficultto produce in such structures than embedded-clause-biased verbs, which are more frequently pro-duced as the main verbs of sentence-complementstructures. We discuss two reasons why the ratewith which verbs are produced as sentence-comp-lement structures may affect difficulty of pro-duction: frequency differences, and differences inmessage formulation.

Frequency is probably among the most heavilyinvestigated factors in the behavioural sciences.Simply put, people are faster, more fluent, andless error prone when executing sequences of be-haviour they have performed more frequently thanwhen executing sequences of behaviours they haveperformed less frequently. This has not beenheavily explored in the sentence-productiondomain, but F. Ferreira and Engelhardt (2006)raise the issue and consider two relevant studies.Tannenbaum and Williams (1968) cued speakersto produce active or passive sentences in miniaturediscourses that sometimes licensed the particularactive or passive structure. Relevantly, actives are amuch more frequent construction than passives(Svartvik, 1966). Tannenbaum and Williamsfound that active-licensing discourses tended toelicit actives and passive-eliciting discourses pas-sives, but in no condition were passives producedwith faster latencies than actives (the strength ofthis conclusion is undermined somewhat by thefact that the latency measure included the durationof the utterance itself, and passive sentences havemore words and morphemes in them than actives;however, in neutral discourses, actives were pro-duced nearly 1.5 s faster than passives, a differencelikely to be much larger than can be accounted forby passives’ additional material). Similarly,F. Ferreira (1994) had speakers produce activesand passives that included verbs that are producedin passives relatively less often versus verbs thatare produced in passives more often (though stillmuch less than half the time). When collapsedacross verb types, formulation latencies (how longspeakers took to indicate they were ready toproduce a sentence) were faster for actives than



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for passive sentences (and here, productionlatencies were onset latencies and did not includeutterance duration). Together, these resultssuggest that speakers can formulate and articulatea more frequent structure (actives) faster than aless frequent structure (passives), consistent withthe possibility that the more frequent structurewas easier to produce.

For the sentence-complement structures underscrutiny here, the relevant frequency difference isfor a particular structure, contingent on the verbthat takes the structure as an argument.Specifically, given a sentence-complement struc-ture, speakers have produced that structure withone set of verbs—embedded-clause-biasedverbs—more frequently than with another set ofverbs—direct-object-biased verbs. This raises thepossibility that the more frequent verb–structurepairing will be easier to produce than the less fre-quent verb–structure pairing. If so, speakers maysay the “that” less in sentence-complement struc-tures with embedded-clause-biased verbs than insentence-complement structures with direct-object-biased verbs, as a reflection of the relativeease of producing the former compared to thelatter.

A closely related result was reported by Gahl andGarnsey (2004). They had speakers produce sen-tences with embedded-clause-biased and direct-object-biased verbs both as sentence-complementstructures (i.e., with an embedded clause) and astransitive structures (i.e., with a direct object).They measured whether speakers reduced the pho-nology of their productions (by deleting the /t/ or/d/), as well as prosodic properties of the pro-ductions. Results showed more deletion of /t/ and/d/ in “bias-matching” contexts (when an embeddedclause was produced with an embedded-clause-biased verb or a direct object with a direct-object-biased verb) than in “bias-violating” contexts(when the bias of the verb and the structure pro-duced mismatched). Similarly, bias-matching pro-ductions were produced with reduced prosody.Speakers tend to reduce their production of morefrequent elements (e.g., Gregory, Raymond, Bell,Fosler-Lussier, & Jurafsky, 1999). This suggeststhat the frequency of a produced structure

contingent on the bias of the verb produced withthat structure can affect production.

Another (not mutually exclusive) reason whyspeakers may find sentence-complement structureswith direct-object-biased verbs to be more difficultto produce than sentence-complement structureswith embedded-clause-biased verbs is due to differ-ences at the level of message formulation (we thankan anonymous reviewer for raising this possibility).Note that in all likelihood, the reason why verbshave the biases they do is because of how speakerstend to use particular verbs to talk about theworld. The verb “accept” is direct-object biasedprobably because when speakers talk about accept-ing, they tend to talk about simple objects ratherthan entire propositions, and so they will usedirect objects; the verb “announce” in contrast isprobably used to announce propositions, and so itwill more often be followed by an embeddedclause. As such, using “accept” to talk about a prop-osition may fit less well with the meaning of“accept” and what it is used to talk about thanusing the verb “announce”. In turn, this maymake it more difficult to formulate sentence-comp-lement structures that use “accept” as the main verbthan sentence-complement structures that use“announce” as the main verb; if so, speakers mayinclude the “that” in sentence-complement struc-tures that have direct-object-biased verbs morethan in sentence-complement structures that haveembedded-clause-biased verbs. Note that the poss-ible effect of formulation difficulty on “that”mention is similar to the result reported byV. S. Ferreira and Hudson (2011), where speakerssaid the “that” in sentence-complement structuresmore when the sentence required adopting theiraddressees’ perspectives than when the sentencerequired adopting their own perspectives—prob-ably a difference in difficulty of messageformulation.

Jaeger (2010) reported an effect similar to theverb-bias effect considered here. He measuredhow often particular verbs in a speech corpus (thePenn Treebank component of the Switchboardcorpus; Godfrey, Holliman, & McDaniel, 1992)were followed by embedded clauses relative toother construction types (which is like verb bias as



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described here, except counting only embeddedclauses and not direct objects) and showed thatthe more a verb tended to be followed by anembedded clause, the less likely the “that” was tointroduce the embedded clause. Similar effects ofomitting optional material have been observed incorpora examining relative clauses (Jaeger, 2006,2011; Levy & Jaeger, 2007; Wasow, Jaeger, &Orr, 2011).

Jaeger positions the results as supportinguniform information density, whereby speakersattempt to spread the informativeness of a sentenceevenly across a sentence. If a verb rarely takes anembedded clause, the arrival of that embeddedclause is surprising and so highly informative. If a“that” introduces the embedded clause, the arrivalof the embedded clause is less surprising and sonot as informative. Thus, by uniform informationdensity, the “that” serves to reduce the “spike” ofinformation that would have accompanied thearrival of an embedded clause following a verbthat is rarely followed by embedded clauses. Thisfits with the Garnsey et al. (1997) effect reportedabove and, though different in interpretation, alsowith the possibility that difficulty affects themention of the “that”.

The present study

Thus, there are two (nonmutually exclusive) expla-nations for the possible effect whereby speakersmention the optional “that” more in sentence-complement structures with direct-object-biasedmain verbs than in sentence-complement structureswith embedded-clause-biased main verbs. Such aneffect (if it holds in online spoken production like itdoes in offline norming and in natural corpora)might reflect a tendency to produce sentence-complement structures with direct-object-biasedmain verbs so that they are easier to understand;or it might reflect that sentence-complement struc-tures with direct-object-biased main verbs areharder to produce. Experiment 1 here verifiedthat in spoken production, speakers include theoptional “that” more in sentence-complementstructures with direct-object-biased main verbsthan in sentence-complement structures with

embedded-clause-biased main verbs. Experiment2 confirmed that this effect was not an artefact ofthe task used in Experiment 1.

Then, Experiments 3a and 3b aim to distinguishthe two explanations just described, to determinewhether speakers say the “that” more in sentence-complement structures with direct-object-biasedmain verbs because they will be easier to understandthat way, because they are harder to produce thatway, or because of a combination of both. Theexperiments do so by dissociating the likelihoodthat a verb is followed by a direct object from thelikelihood that it is followed by an embeddedsubject. Note that “that” mention should varywith the likelihood that a verb is followed specifi-cally by a direct object only if production is sensitiveto the potential disruptiveness of a garden path,because it is the speaker’s comprehender who willbe sensitive to the fact that a noun phrase after averb is likely to be a direct object. In contrast, if pro-duction is sensitive only to difficulty of production,then the likelihood that a verb is followed by adirect object—a structure that the speaker doesnot intend to produce—is irrelevant. By dissociat-ing the likelihoods of a direct object versus anembedded clause, Experiments 3a and 3b candetermine whether production is sensitive to thelikelihood of a direct object, which should be thecase if production is sensitive to the potential dis-ruptiveness of a garden path, or if it is sensitiveonly to the likelihood that a verb is followed byan embedded clause, which should be the case ifproduction is sensitive only to difficulty ofproduction.

All experiments also included a manipulation ofthe plausibility of the embedded-subject argumentas a direct object (following Garnsey et al., 1997).For example, “The proud mother announced(that) the wedding . . . ” includes an embeddedsubject that is plausible as a direct object, whereas“Theproudmother announced (that) theflowers . . . ”includes an embedded subject that is implausible asa direct object. Garnsey et al. (1997) found thatreaders generally showed larger garden-patheffects when the embedded subject was a plausibledirect object in these sentences. The productionexperiments here, however, never showed any



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effect of (or interaction with) the plausibilitymanipulation, and so it is not discussed further(the comprehension experiment shows a plausi-bility effect, replicating Garnsey et al., 1997, sothat effect is briefly reported).

EXPERIMENT 1

The materials for Experiment 1 were taken fromGarnsey et al. (1997). Speakers produced sen-tence-complement structures including threetypes of verbs: direct-object-biased verbs (verbsthat relatively frequently take direct objects),embedded-clause-biased verbs (verbs that relativelyfrequently take embedded clauses), and equibiasedverbs (verbs that take direct objects and embeddedclauses at intermediate rates relative to the othertwo verb classes). They produced sentences in amemory-based sentence-production task.Speakers read a critical sentence and a filler sen-tence in (apparently) random order each for 5 sand were asked to remember them. They werethen prompted to produce the sentences back oneat a time in (apparently) random order, as cued bythe main subject and verb from each sentence.Half of the critical sentences speakers originallyread included the “that”, and half did not (counter-balanced across the other factors). Speakers in taskslike these have imperfect memory for the “that”, assentences are recalled based largely on the gist ofthe originally read sentence and less based on thesuperficial form of the sentence (e.g., E. Bates,Masling, & Kintsch, 1978; Lombardi & Potter,1992; Sachs, 1967). This allows other factorssuch as the bias of the main verb to influence speak-ers’ “that” mention (see V. S. Ferreira, 2003;V. S. Ferreira & Dell, 2000; V. S. Ferreira &Firato, 2002; Lee & Gibbons, 2007). If thepattern found by Garnsey et al. (1997) withwritten sentence completion, as well as what hasbeen revealed using corpus based evidence (Jaeger,2010) happens also in online spoken production,then speakers should say the “that” most in sen-tences with direct-object-biased verbs and least insentences with embedded-clause-biased verbs,and equibiased verbs should be in between.

Method

SubjectsForty-eight members of the University ofCalifornia, San Diego (UCSD) community partici-pated in Experiment 1. They received either coursecredit or cash payment. All reported learningEnglish as their first language.

ApparatusSpeakers were tested on Macintosh computersusing PsyScope (Cohen, MacWhinney, Flatt, &Provost, 1993). Head-worn microphones wereconnected to standard audio cassette recordersand a PsyScope serial button box to record speakers’utterances and to detect voice onsets.

ProcedureSpeakers pressed the space bar to begin each trial.After a 1-s blank interval, speakers saw the firstsentence to be remembered (all stimuli werecentred vertically and horizontally on the screen),which remained on the screen for 5 s. Speakerswere asked to read the sentence aloud, to ensureaccurate encoding. After another 1-s blank interval,speakers saw the second sentence to be remem-bered, also for 5 s. After a 1-s blank interval, speak-ers were shown the main subject and verb of one ofthe just-presented sentences and were asked to sayback the complete original sentence. They weregiven 4 s to produce back the sentence (as triggeredby a voice key), at which point a beep sounded.Speakers were encouraged to attempt to recall thesentence before beginning to speak, to reduce dis-fluency. The other sentence was then promptedsimilarly.

The order that sentences were presented forencoding and recall was pseudorandomly deter-mined. From the speakers’ perspective, the sen-tences can be prompted in the same or in theopposite order as presented; half of all criticaltrials were presented in each of these orders, sothat speakers would not be biased to anticipatethe recall of the first- or second-presented sentence(thus requiring speakers to remember both sen-tences). However, to reduce the likelihood thatspeakers would remember the critical sentence



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verbatim, the order where the critical sentence waspresented second and then immediately promptedfor recall was never used and was replaced withthe order where the critical sentence was presentedfirst and then prompted second. This means thaton half of trials, the encoding and recall of the criti-cal sentence was separated by both the encodingand the recall of the filler sentences, whereas onthe other half of trials, the encoding and recall ofthe critical sentence was separated by either theencoding or the recall of the filler sentence.

The experimental session began with a briefprocedure to calibrate the voice key. Speakerswere then given the instructions for the experiment,including a step-by-step presentation of the pro-cedure using a sample sentence. Speakers werethen presented with five practice trials that werethe same in form as the critical trials.

Materials, design, and analysisThe critical sentences were taken from Garnseyet al. (1997). These were 48 pairs of sentence-complement structures consisting of a mainsubject, a main verb, an optional “that”, anembedded subject, and then the rest of theembedded clause. The main subject was alwaysthree words long and typically was a determiner,an adjective, and a noun. The main verb wasdirect-object biased, equibiased, or embedded-clause biased, with 16 pairs of sentences of eachbias. Each sentence had a different main verb. Inone sentence of each pair, the embedded subjectwas a potentially plausible direct object, whereas

in the other sentence of the pair, it was implausible(as noted above, this manipulation was ineffectiveand so is not formally reported). The remainderof the embedded clauses continued to completemultiple-word verb phrases. Examples of sentencesincluding verbs of each verb bias are shown inTable 1, along with the percentages of sentencesof each verb type that were completed as one ofthe two critical sentence types (from normativedata collected by Garnsey et al., 1997).

One factor of interest was manipulated: verb bias,referring to whether the sentence-complementstructures speakers produced included main verbsthat were direct-object-biased, equibiased, orembedded-clause biased. This factor was manipu-lated within speakers and between items. The sen-tences were manipulated also according to twoadditional factors: The embedded subject of the sen-tence was either a plausible or an implausible directobject, and the optional “that” was included oromitted in the sentence that speakers encoded. Allfactors were manipulated in counterbalancedfashion, such that each speaker saw each verb onceand saw equal numbers of sentences with plausibleand implausible embedded subjects and with andwithout the “that”; every verb was presented in a sen-tence with plausible and implausible embedded sub-jects and with and without the “that” across subjects.

The proportion of sentences that speakers pro-duced with the “that” was calculated for eachspeaker across sentences (in the speaker analysis)and for each sentence across speakers (in the itemsanalysis) within each condition. (Percentages are

Table 1. Examples of sentences used in Experiment 1

Verb type Example sentence

Direct-objectcontinuations

(%)

Embedded-clausecontinuations

(%)

Direct-object biased The talented photographer accepted (that) the money could notbe spent yet.

69.7 13.7

Equibiased The weary traveler claimed (that) the luggage had been stolen inRome.

35.3 36.1

Embedded-clause biased The proud mother announced (that) the wedding would be a bigevent.

11.8 58.7

Note: Embedded-clause continuations and direct-object continuations from normative data reported in Garnsey et al. (1997).



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reported for readability.) These proportions wereentered into two 3× 2 analyses of variance(ANOVAs) with the factors verb bias (direct-objectbiased, equibiased, embedded-clause biased) and“that” inclusion (“that” included or omitted in theoriginally presented sentence). ANOVAs acrossspeakers (F1) and items (F2) are presented. All ana-lyses were also conducted on arcsine-transformedproportions; all significant effects were also signifi-cant after the arcsine transformation. Variation isreported with 95% confidence interval halfwidths(CIs) based on single degree-of-freedom compari-sons as calculated from ANOVA output (Loftus &Masson, 1994; Masson & Loftus, 2003).Significant effects achieved the .05 level or better.

In addition to ANOVAs on aggregate pro-portion data, we analysed the data using logisticregressions (linear mixed-effects models with alogit link) on the individual trial-level data (Jaeger,2008). In order to fit the models, the lmer functionfrom the lme4 package (D. Bates, Maechler, &Dai,2009) was used within the R Environment forStatistical Computing (R Development CoreTeam, 2011). For Experiment 1, the modelsincluded verb bias, defined as a continuous variable,and whether the sentence was presented with a“that” as fixed effects and subjects and items ascrossed random effects (Baayen, Davidson, &Bates, 2008). Continuous verb-bias values weretaken from norms collected by Garnsey et al.(1997) and were defined as the proportion of sen-tences for a particular verb that completed with

embedded-clause continuations divided by thesum of the proportions for that verb completedwith embedded-clause continuations plus direct-object continuations. The random effects structureincluded random intercepts and random slopes ofverb bias and “that”-presentation for subjects andrandom intercepts and random slopes of “that”-presentation for items (because verb bias is abetween-items variable). Both “that”-presentationand verb bias were centred to allow for the interpret-ation of the main effects at the average value of theother factor (i.e., regardless of “that”-presentationand at the average value of verb bias). Because thedependent measure is a binary outcome (i.e.,whether the subject mentioned “that” or did not),we used a generalized linear mixed model with alogit link, for which the test statistic is a z-value.The b values are estimates of effect size in logitspace so they cannot be directly interpreted.

Results

Speakers produced 2,304 critical sentences.Sentences were excluded from analysis if (a) theoriginally presented sentence was not read aloudaccurately (169 sentences); (b) the speaker did notrecall a sentence-complement structure (558 ofthe remaining sentences); (c) the speaker did notproduce the correct main verb (19 of the remainingsentences). In total, 1,558 (67.6%) of sentencesremained for analysis. Table 2 shows the percen-tages of exclusions per condition.

Table 2. Experiment 1 results

Experimental condition Excluded trials (%) “That” produced (%)

Originally encoded with “that”Direct-object biased 37.8 88.9Equibiased 31.8 85.4Embedded-clause biased 29.7 74.9

Originally encoded without “that”Direct-object biased 35.4 72.6Equibiased 33.3 61.8Embedded-clause biased 26.3 57.3

Note: Excluded trials and percentages of “that” produced in sentence-complement structures with direct-object-biased, equibiased, andembedded-clause-biased verbs when originally encoded sentences included or omitted “that”.



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The percentages of “that” speakers producedin sentence-complement structures with direct-object-biased, equibiased, and embedded-clause-biased verbs are shown in Figure 1. Thesepercentages are reported in Table 2 separately forwhether a “that” was in the original sentence.Speakers produced the “that” most in sentence-complement structures with direct-object-biasedverbs (80.8% of sentences) and least in sentence-complement structures with embedded-clause-biased verbs (66.1% of sentences), with equibiasedverbs falling between these (73.6% of sentences).This led to a significant main effect of verb bias,F1(2, 94)= 15.1, CI=+5.3%, F2(2, 45)= 7.98,CI=+7.2%. The main effect of whether the orig-inal sentence included the “that” was also signifi-cant, F1(1, 47)= 46.9, CI=+5.6%, F2(1, 45)=51.4, CI=+5.3%. This shows that speakers saidthe “that” more when the original sentenceincluded the “that” than when the original sentenceomitted it. The interaction between these factorswas nonsignificant, F1(2, 94)= 1.05, CI=+7.6%, F2(2, 45)= 1.39, CI=+9.1%.

Mixed-effects analyses revealed similar results tothe ANOVAs: There was a significant effect of

verb bias, b= –1.57, SE= 0.40, z= –3.93,p, .005, with speakers saying “that” less as thelikelihood that the verb implied an embedded-clause structure increased. Whether the probe sen-tence included a “that” also significantly increasedthe likelihood that subjects would produce a“that”, b= 1.54, SE= 0.19, z= 8.05, p, .001,and there was no interaction, such that the effectwas not significantly different across differentdegrees of verb bias (p. .26).

Discussion

The results of Experiment 1 confirm that verb biassystematically affects “that” mention: Speakers pro-duced the optional “that” more in sentence-complement structures with main verbs that areoften produced with direct objects than in sen-tence-complement structures with main verbs thatare often produced with embedded clauses; sen-tence-complement structures with main verbs thatwere intermediate in this bias were produced with“that” at an intermediate rate. This replicates andextends observations with written and corpusmethods and is consistent with both accounts

Figure 1. Experiment 1 results. Percentages of “that” produced in sentence-complement structures with direct-object-biased, equibiased, andembedded-clause-biased verbs. Error bars show 95% confidence interval halfwidth for the main effect of verb type.



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outlined in the introduction: Speakers may say the“that” more in sentence-complement structureswith main verbs that usually take direct objects,because comprehenders find garden paths in sen-tences with such verbs more disruptive; or speakersmay say the “that” more in sentence-complementstructures with main verbs that rarely takeembedded clauses because they find producingsuch structures with those verbs to be relativelymore difficult, and speakers say “that” in moredifficult-to-produce sentences.

One concern with Experiment 1 comes from thememory-based sentence-production task that wasused. Specifically, in this task, speakers must readthe entire sentence-complement structure beforeproducing it. Presumably, as in the Garnsey et al.(1997) study, speakers will experience a moredisruptive garden path when reading (“that”-less)sentence-complement structures with direct-object-biased main verbs than when reading(“that”-less) sentence-complement structures withembedded-clause-biased verbs. This raises thepossibility that it was the disruption that speakersthemselves experienced when reading the sentencethat influenced “that” mention rather than the biasof the verb. Experiment 2 addressed this concern.

EXPERIMENT 2

Experiment 2 was a replication of Experiment 1with two main differences. First, instead of amemory-based sentence-production task, speakersin Experiment 2 were tested with a sentence-combi-nation task. Here, speakers were given two relativelysimple sentences and were asked to combine theminto one longer sentence. As such, speakers neverread complete sentence-complement structures inExperiment 2, and so would not experience anygarden paths before producing critical sentences. Ifthe result in Experiment 1 happened because speak-ers read sentences before producing them, then theeffect of verb bias should not be observed inExperiment 2. Second, speakers produced differentsentences (provided by Susan Garnsey, personalcommunication, July 12, 2002). The equibiased con-dition was eliminated, and additional sentences were

added to the direct-object-biased and embedded-clause-biased conditions.

Method

SubjectsFifty-one speakers from the same population asthat in Experiment 1 participated in Experiment2. Data from four speakers were removed from ana-lyses because recording difficulties caused nearly allof their productions to be lost, and data from twomore speakers were eliminated because exclusions(described below) eliminated more than 75% oftheir critical productions. (All subjects tested inExperiments 1 and 3 exceeded this criterion.)

ApparatusApparatus was the same as that in Experiment 1.

ProcedureAt the beginning of each trial, speakers were shownthe current trial number and pressed the space barto proceed. After a 500-ms blank interval, speakerssaw a fixation point for 1 s (all stimuli were centredvertically and horizontally). Two sentences werethen presented consecutively, each for 3 s after a500-ms blank interval. After another 500-msblank interval, a prompt to combine the two sen-tences (“. ,”) was shown. The prompt remainedon the screen until the voice key detected thespeaker’s production.

Speakers were given a cover story that they werea story writer for a high-level newspaper, whichtended to publish stories with longer and morecomplicated sentences. They were thus to practisetaking simple sentences and combining them intomore complex ones. Speakers were specificallyinstructed not to change the meaning that thetwo sentences expressed.

The session began with instructions and prac-tice, as in Experiment 1. There were 12 trials inthe practice session.

Materials, design, and analysisEighty pairs of critical sentence-complement struc-tures were developed. These came from 40 differentverbs, such that every verb was used in two pairs of



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sentences. The constitution of the sentence-complement structures was the same as that inExperiment 1. The pairs implemented a plausibilitymanipulation, as in Experiment 1. Each (critical andfiller) sentence was broken into two simpler sen-tences. For the sentence-complement structures,these were one sentence including the mainsubject, main verb, and “something” (e.g., “Thetalented photographer accepted something”) andanother including the rest of the sentence (e.g.,“The money could not be spent yet”). Sixty-eightfiller sentences were added to each list, so that speak-ers produced a total of 148 sentences. Fillers weredesigned to elicit sentences of different types(other than sentence-complement structures),including simple sentences, relative clause structures,and so forth. Table 3 shows an example of sentence-complement structures with each main-verb bias.

The experiment included one primary factor ofinterest: The main verb in the sentence-comp-lement structure was either direct-object biased orembedded-clause biased. This factor was manipu-lated within subjects and between items. Oneother factor, the plausibility of the embeddedsubject as a direct object, was crossed with verbbias and was within subjects and items. Statisticalanalyses were conducted as in Experiment 1,except dropping the factor assessing whether the“that” was originally presented.

Mixed-effects analyses for Experiment 2 weresimilar to those for Experiment 1 with the fol-lowing exceptions. The only fixed effect wasverb bias, which included only direct-object-biased verbs and embedded-clause-biasedverbs. Only random intercepts were used for

items, since verb bias is a between-items factor.Random intercepts and random slopes of verbbias were included for subjects.

Results

A total of 3,600 productions were eligible for analy-sis. Trials were eliminated if (a) the speaker did notproduce a sentence-complement structure (476trials) or (b) the speaker produced the wrongmain verb (482 remaining trials). In total, 2,642(73.4%) of sentences remained to be analysed.Table 3 reports percentages of excluded trials percondition.

Figure 2 shows the percentages of “that” speakersproduced in sentence-complement structures withdirect-object-biased and embedded-clause-biasedmain verbs. Speakers produced the “that” about7.2% more in sentence-complement structureswith direct-object-biased main verbs (70.5% of sen-tences) than in sentence-complement structureswith embedded-clause-biased main verbs (63.3%of sentences). This difference was significant, F1(1,44)= 16.2, CI=+3.6%, F2(1, 78)= 11.4,CI=+4.6%. Mixed-effects analyses revealed a sig-nificant effect of verb bias, b= –0.97, SE= 0.33,z= –2.98, p, .005, with fewer “that”s beingincluded as the likelihood of the verb taking anembedded clause increases.

Discussion

Experiment 2 replicates Experiment 1: Speakersproduced the “that” more in sentence-complementstructures with main verbs that are direct-object

Table 3. Examples of sentences used in Experiment 2



(%)

Embedded-clausecontinuations

(%)

Excludedtrials(%)

Direct-objectbiased

The talented photographer accepted (that) themoney could not be spent yet.

67.7 12.6 31.9

Embedded-clausebiased

The ticket agent admitted (that) the mistake hadbeen careless and stupid.

10.2 57 21.3




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biased than in sentence-complement structureswith main verbs that are embedded-clause biased.Thus, the pattern observed in these online pro-duction tasks is not because of any effect of compre-hending a full sentence-complement structurebefore producing one, because speakers inExperiment 2 did not read full sentence-comp-lement structures before producing them.

Experiments 1 and 2 demonstrate that speak-ers’ mention of the “that” in a sentence-complement structure is sensitive either to howoften the main verb in the sentence-complementstructure occurs with direct objects, or to howoften the main verb in the sentence-complementstructure occurs with embedded clauses, or both.The first of these (degree of direct-object bias)should influence “that” mention only if speakersare sensitive to the degree of potential disruptive-ness of the garden path in a sentence-complementstructure. In contrast, only the second ofthese (degree of embedded-clause bias) shouldinfluence “that” mention if speakers find it moredifficult to produce sentence-complementstructures with verbs that are not produced insuch structures relatively often. But because theverb classes in Experiments 1 and 2 (inversely)

confounded the degree of direct-object biasand the degree of embedded-clause bias,Experiments 1 and 2 are unable to distinguishthese alternatives.

EXPERIMENT 3

In Experiment 3, a third class of verb is introducedthat unconfounds the two biases: neither-biasedverbs. These are verbs like “agree” that rarelytake direct objects or embedded-clause arguments,because they instead often take other sorts of argu-ments (like prepositional phrases, infinitivalclauses, and so forth). In particular, here,neither-biased verbs took direct objects about15% of the time and embedded clauses about15% of the time (see Table 4). Consider first thepossibility that speakers are sensitive to how dis-ruptive their produced garden paths might be.Upon hearing a neither-biased verb, a comprehen-der might immediately estimate that the likeli-hood of a direct object is low (15%); if so, thenthe garden path they experience will be mild.This is the same likelihood that an embedded-clause-biased verb here has of taking a direct

Figure 2. Experiment 2 results. Percentages of “that” produced in sentence-complement structures with direct-object-biased and embedded-clause-biased verbs. Error bars show 95% confidence interval halfwidth for the main effect of verb type.



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object (15%) and a much lower probability than adirect-object-biased verb has of taking a directobject (73%; see Table 4). Thus, if speakers saythe “that” to avoid especially disruptive gardenpaths, then they should say the “that” equallyrarely in sentences that have neither- andembedded-clause-biased verbs, and they shouldsay “that” much more in sentences that havedirect-object-biased verbs. A more sophisticatedcomprehension-sensitive account is that uponcomprehending a neither-biased verb followedby a noun phrase, a comprehender might estimatethe likelihood that the noun phrase is a directobject at about 50%. This would be because,although the likelihood of a direct object overallis just 15%, the comprehender will encounter thenoun phrase before the potential garden pathand so may be able to discard from considerationany outcome that is not a noun phrase evenbefore being garden pathed. This leaves directobjects and embedded clauses, each having a15% overall likelihood, meaning that each has a50% likelihood relative to the other [15%/(15%+ 15%)]. This 50% likelihood of a directobject with neither-biased verbs compares to ananalogous 16% likelihood of a direct object withembedded-clause-biased verbs [14%/(14%+72%)] and an 83% likelihood for direct-object-

biased verbs [73%/(73%+ 15%)]. Therefore, onthis more sophisticated comprehension-sensitiveaccount, speakers should say the “that” most insentences with direct-object-biased verbs (83%chance of a direct object), at intermediate ratesin sentences with neither-biased verbs (50%chance of a direct object), and least withembedded-clause-biased verbs (16% chance of adirect object).

Meanwhile, if speakers are sensitive to how dif-ficult a sentence is to produce, and if it is harder toproduce sentence-complement structures as afunction of how often the verbs in those structuresare produced with embedded clauses, then onlythe likelihood (or frequency, as far as productionis concerned) of a verb taking an embeddedclause is relevant. Embedded-clause-biased verbsare produced with embedded clauses about 73%of the time (see Table 4), whereas direct-object-biased and neither-biased verbs are producedwith embedded clauses just 15% of the time. Ifthe mention of “that” is sensitive just to pro-duction difficulty as reflected by frequency, speak-ers should say the “that” less in sentences withembedded-clause-biased verbs than in sentenceswith neither- and direct-object-biased verbs,which in turn should be produced with the“that” about equally.

Table 4. Examples of sentences used in Experiments 3a and 3b



(%)

Embedded-clause

continuations(%)

Excluded trials

Experiment3a(%)

Experiment 3b

Plausiblecondition

(%)

Implausiblecondition

(%)

Direct-objectbiased

Jenny anticipated (that) the turn would beextremely sharp.

73.1 14.7 23.2 6.5 3.3

Neither-biased

Karen agreed (that) the deal was as appealingas possible.

15.3 15.3 24.3 7.6 3.3

Embedded-clausebiased

Kevin assumed (that) the blame was going tohead his way.

13.7 72.4 11.5 1.1 0.0




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Thepredictionsof the twocomprehension-sensitiveand the production-sensitive accounts are shown inFigure 3. According to all accounts, speakers shouldsay the “that” more in sentences with direct-object-biased verbs than in sentences with embedded-clause-biased verbs, as observed in Experiments 1 and2. Critical are neither-biased verbs. On either compre-hension-sensitive account, speakers should say the“that” less in sentences with neither-biased verbs thanin sentences with direct-object-biased verbs. The pro-duction-sensitive account, in contrast, predicts thatspeakers should say the “that” in sentences withneither-biased verbs and in sentences with direct-object-biased verbs about equally.

(Note that these predictions regarding neither-biased verbs differ from predictions regarding theequibiased verbs from Experiment 1. Critical isthat the equibiased verbs in Experiment 1 takeembedded clauses at intermediate rates (36%),whereas neither-biased verbs in Experiment 3 takeembedded clauses at low rates (15%). As a result,whether speakers mention the “that” to avoid disrup-tive garden paths or as a result of producing a moredifficult to produce sentence, speakers should say the“that” at intermediate rates with equibiased verbs inExperiment 1. Put somewhat differently, inExperiment 1, the three verb types inversely con-founded the likelihood that verbs take direct

objects versus embedded clauses; in Experiment 3,the neither-biased verbs break this confound.)

Experiment 3 consists of two subexperiments(Experiments 3a and 3b). Experiment 3a tests pro-duction, to see how often speakers say the “that” insentence-complement structures with neither-biased verbs, as compared to sentence-complementstructures with direct-object- or embedded-clause-biased verbs. Note, however, that previous workhas not investigated the comprehension of sen-tence-complement structures with neither-biasedverbs, so Experiment 3b assessed whether compre-henders indeed take noun phrases after neither-biased verbs to be direct objects less than nounphrases after direct-object-biased verbs.

EXPERIMENT 3A

Method

SubjectsSeventy-two speakers from the same population asthat in Experiment 1 participated in Experiment 3a.

ProcedureThe procedure was identical to that inExperiment 2.

Figure 3. Predicted percentages of “that” produced in sentence-complement structures with direct-object-biased, neither-biased, andembedded-clause-biased verbs for Experiment 3a.



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Materials, design, and analysisForty-two new pairs of sentence-complementstructures were constructed. The main subjects ofthese were single proper names. The main verbwas direct-object biased, embedded-clause biased,or neither-biased. The embedded subject was asimple noun phrase that was manipulated forplausibility. The rest of the embedded clauseincluded at least two more words. Table 4 showsan example of sentence-complement structureswith main verbs of each bias. Forty-two filler sen-tences that were designed to elicit a variety of struc-tures (other than sentence-complement structures)were added to each list.

The design and analyses were the same as thosein Experiment 1, but with neither-biased verbsinstead of equibiased verbs and without anymanipulation of whether the original sentenceincluded a “that” (because the sentence-combi-nation paradigm does not require sentences toinclude or omit the “that”). Mixed-effects analyseswere similar to those in Experiment 2 with theaddition of the neither-biased verbs as a level ofverb bias.

Results

A total of 3,024 productions were eligible for analy-sis. Trials were excluded if (a) subjects did notproduce a sentence-complement structure (538trials), or (b) the sentence was produced with thewrong main verb (57 remaining trials). In all, 2,429trials (80.3%) remained for analysis. Percentages ofexcluded trials per condition are shown in Table 4.

Figure 4 shows the percentages of “that” producedin sentence-complement structures with direct-object-biased, neither-biased, and embedded-clause-biased main verbs. As in Experiments 1 and2, speakers produced the “that” more in sentence-complement structures that had direct-object-biased main verbs (71.2%) than in sentence-comp-lement structures that had embedded-clause-biasedverbs (63.1%). Importantly, speakers did notproduce the “that” in sentence-complement struc-tures with neither-biased main verbs statisticallyless than in sentence-complement structures withdirect-object-biased main verbs, as speakers pro-duced the “that” in 69.1% of sentence-complementstructures with neither-biased verbs. The main

Figure 4. Experiment 3a results. Percentages of “that” produced in sentence-complement structures with direct-object-biased, neither-biased, and embedded-clause-biased verbs. Error bars show 95% confidence interval halfwidth for the main effect of verb type.



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effect of verb bias was significant by subjects, F1(2,142)= 9.21, CI=+3.9%, though not by items,F2(2, 39)= 1.57, CI=+9.5%; the items analyseshas substantially less statistical power both becauseverb type is manipulated between items andbecause only 14 items per condition could befound, given limitations on the number of verbsthat are neither biased. Note that given the by-sub-jects confidence interval of 3.9%, the 2.1% differencefound between sentences with direct-object-biasedverbs versus with neither-biased verbs is nonsignifi-cant. Meanwhile, the 8.1% difference betweensentences with direct-object- versus embedded-clause-biased verbs was significant, as was the 6.0%difference between sentences with neither-biasedversus embedded-clause-biased verbs. This is mostconsistent with the pattern shown in Figure 3c, theone predicted if verb bias effects reflect difficulty ofproduction. The small number of items also compro-mised power in the mixed-effects analyses, as therewas no significant difference between the direct-object-biased verbs and either the neither-biased orthe embedded-clause-biased verbs (p. .68).

Discussion

Speakers produced the “that” in sentence-comp-lement structures with verbs biased neither towarddirect objects nor toward embedded clauses relativelyoften—statistically as often as they produced the“that” in sentence-complement structures withverbs biased toward direct objects, and significantlymore often than they produced the “that” in sen-tence-complement structures with verbs biasedtoward embedded clauses. Because the nounphrases after neither-biased verbs are less likely tobe direct objects, the observation that speakers didnot say the “that” in sentence-complement structureswith neither-biased verbs less than they did in sen-tence-complement structures with direct-object-biased verbs suggests that it is not a sensitivity tothe disruptiveness of a garden path that drives speak-ers’ mention of the “that”. Rather, neither-biasedand direct-object-biased verbs are similar in thatthat both types of verbs are rarely produced withembedded clauses, and this is probably what drivesthe higher “that” mention in both cases.

EXPERIMENT 3B

The logic of Experiment 3a relies on the claim thatthe difficulty induced by a garden path is driven atleast in part by how likely a noun phrase after a verbis to be a direct object—the less so, the lessdisruptive the interference should be when thedirect-object analysis proves incorrect. If not—ifcomprehension processes suffer equal garden-patheffects regardless of how often a main verb takes adirect object argument (say, because garden pathsare sensitive only to how often a main verb takes asentence complement)—then direct-object-biasedverbs and neither-biased verbs should be equally dis-ruptive. If direct-object-biased verbs and neither-biased verbs are equally disruptive, then on acomprehension-sensitive account (as on a pro-duction-sensitive account), speakers should say the“that” about equally in sentences with the twotypes of verbs, as was observed in Experiment 3a.

Experiment 3b assessed whether the postverbalnoun phrases in sentence-complement structureswith neither-biased main verbs are less likely tobe taken as a direct object than postverbal nounphrases in sentence-complement structures withdirect-object-biased main verbs. If so, then it islikely that sentence-complement structures withneither-biased verbs cause less disruptive gardenpaths. To do so, the experiment used a sentence-completion task to assess the comprehensionbiases of the to-be-produced sentence-complementstructures when they had direct-object-biased,embedded-clause-biased, and neither-biased mainverbs. For critical sentences, subjects were pre-sented with the main subject, main verb, andembedded subject of the sentence-complementstructure speakers produced in Experiment 3a(e.g., “Jenny anticipated the turn . . . ”) and wereasked to complete the sentence as they wished.To do so, subjects had to read and understandthe main subject, main verb, and postverbal nounphrase. This requires that the subject interpret thepostverbal noun phrase as an embedded subject, adirect object, or some other type of argument.The subjects’ completion was then analysed todetermine how they interpreted the postverbalnoun phrase. We expected subjects to interpret



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postverbal noun phrases after embedded-subject-biased main verbs to be embedded subjects morethan postverbal noun phrases after direct-object-biased verbs, implying that subjects would sufferless of a garden path with embedded-subject-biased verbs. Of particular interest is whether sub-jects interpreted the postverbal noun phrases afterneither-biased verbs as direct objects less than thepostverbal noun phrases after direct-object-biasedverbs, which on a comprehension-sensitiveaccount of “that”-mention predicts that speakersshould say the “that” less in sentence-complementstructures with neither-biased verbs.

It is worth noting that this task is not a directassessment of the comprehension of garden-pathsentences. We did design and execute an eye-track-ing experiment to assess the disruptiveness of thesentences in Experiment 3a directly. Resultsshowed no differences among any conditions atall, including between sentences with direct-object- and embedded-clause-biased verbs, failingto replicate Garnsey et al. (1997). We assumethat because the sentences in Experiment 3a werenot designed for an eye-tracking study, their prop-erties rendered them a poor fit for proper assess-ment using eye tracking. As such, we elected touse the simpler sentence-completion methodologyused here, so that we could assess the exact sen-tences used in Experiment 3a, even if the measureonly indirectly indexes the likelihood that a com-prehender will interpret the postverbal noun asthe direct object, thereby leading to a garden path.

Method

SubjectsTwenty-six subjects from the same population as thatin Experiment 1 participated in Experiment 3b.

ProcedureSubjects completed a web-based form. For eachstimulus, subjects were presented with the writtenbeginning of a sentence on one line. The next linewas a blank slot. Subjects were instructed to completeeach sentence by entering text into the blank slot witha completion that used asmanywords as theywished,

but that must include at least one word. Subjectscompleted the form at their own pace.

Materials, design, and analysisExperiment 3b tested truncated forms of the sen-tences constructed for Experiment 3a. All criticalsentences were truncated after the embedded-subject noun phrase. Half of the sentences includedthe “that”, and half did not, counterbalanced acrosssubjects and items. Across all eligible trials, 97.8%sentences with “that” were completed as sentence-complement structures, so trials with the “that” arenot considered further. Filler sentences were trun-cated at a point after the main verb but before theend of the sentence. Note that the postverbal nounphrases in Experiment 3a were manipulated forplausibility, and so for comparability, the postverbalnoun phrases in Experiment 3b were manipulatedfor plausibility as well. Because this manipulationhad a strong effect on the sentence-completionresults, these are analysed further below.

A research assistant naive to the experimentalhypotheses coded all sentence completions forwhether the postverbal noun phrase was interpretedas a direct object, an embedded subject, or someother argument. The main dependent variable isthe proportion of trials where subjects took thepostverbal noun phrase as a direct-object argument.Sentences were manipulated for whether the mainverb was embedded-clause biased, direct-objectbiased, or neither biased, as well as for the plausi-bility of the postverbal noun phrase as a direct-object noun phrase. Two items were excludedfrom the items analyses because of empty cells.

Mixed-effects models in Experiment 3b weresimilar to those in Experiment 3a, with the inclusionof plausibility of the postverb noun (centred) as adirect object as a fixed effect and random slopesfor subjects and items. Instead of “that”-inclusionas the dependent variable, the dependent variablewas whether the subject completed the sentencewith a direct-object interpretation.

Results

A total of 546 sentence completions were eligible foranalysis. Of these, 20 were excluded because subjects



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completed sentences with nonsensical completions,leaving 526 trials (96.3%) for analysis. Percentages ofexcluded trials in each condition are shown inTable 4.

Figure 5 shows the percentages of postverbalnoun phrases interpreted as direct-object nounphrases as a function of the bias of the main verband the plausibility of the postverbal noun phraseas a direct object. Postverbal noun phrases afterdirect-object-biased main verbs were 16.9% morelikely to be interpreted as direct objects (63.5%)than postverbal noun phrases after neither-biasedverbs (46.6%). At the same time, postverbal nounphrases after direct-object-biased main verbs were42.8% more likely to be interpreted as directobjects than postverbal noun phrases afterembedded-clause-biased verbs (20.7%). Thesedifferences led to a significant effect of verb bias,F1(2, 50)= 36.6, CI=+10.1%, F2(2, 37)= 9.6,CI=+19.6%. Most important is the observation

that subjects took the postverbal noun phrasesafter neither-biased verbs to be direct objects16.9% less than the postverbal noun phrases afterdirect-object-biased verbs, which (given the10.1% confidence interval on the main effect ofverb type) is a significant difference (however, dueto the small number of items and the resultantgreater variability, this difference was marginallysignificant by items, p, .07).

Postverbal noun phrases that were plausibledirect objects were 34.6% more likely to be inter-preted as direct objects than postverbal nounphrases that were implausible direct objects(60.9% vs. 26.3%), a significant difference, F1(1,25)= 121, CI=+6.5%, F2(1, 37)= 40.1,CI=+10.7%. Plausibility and verb type interactedby subjects only, F1(2, 50)= 7.81, CI=+9.8%,F2(2, 37)= 1.99, CI=+18.6%, reflecting theobservation that the plausibility difference was

Figure 5. Experiment 3b results. Percentages of postverbal noun phrases interpreted as direct objects with main verbs that are direct-objectbiased, neither-biased, and embedded-clause biased and when postverbal noun phrases were plausible or implausible as direct objects. Errorbars show 95% confidence interval halfwidth for the plotted interaction effect.



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smaller for embedded-clause-biased verbs (18.9%)than for the direct-object-biased (43.7%) orneither-biased (41.3%) verbs. As this interactionis not pertinent to the primary issues investigatedin this paper, it is not discussed further.

Mixed-effects analyses revealed a significanteffect of verb bias, b= –6.46, SE= 0.87,z= –7.39, p, .001, with fewer sentences beingcompleted with direct-object interpretations asthe likelihood of the verb taking an embedded-clause structure increased. There was a significanteffect of plausibility, b= 3.10, SE= 0.49, z=6.33, p, .001, such that sentence fragments withnouns that were more plausible as direct objectswere more likely to be completed with direct-object interpretations. There was a significantinteraction between plausibility of the noun andverb bias, b= –3.21, SE= 1.52, z= –2.11,p, .05, with the effect of plausibility beingsmaller as the likelihood for the verb to take anembedded clause increased.

Discussion

Experiment 3a revealed that speakers did not con-sistently mention the “that” in sentence-comp-lement structures with neither-biased verbs lessthan in sentence-complement structures withdirect-object-biased verbs. That is, speakerstreated sentence-complement structures withneither- and direct-object-biased verbs the same,even though comprehenders ought to take anyimmediate postverbal noun phrase as less likelyto be a direct object after neither-biased verbsthan after direct-object-biased verbs. Experiment3b confirmed this latter observation, showingthat when comprehenders were presented withnoun phrases immediately after neither-biasedverbs, they interpreted them as direct objects lessthan noun phrases after direct-object-biasedverbs. This suggests that sentences with neither-biased verbs probably cause weaker garden paths,though direct demonstration of this effect withsentences designed for comprehension studywould strengthen this conclusion. (It is reassuring,however, that plausibility affected the likelihoodthat subjects took postverbal noun phrases as

direct objects, which is analogous to the garden-path effects reported in Garnsey et al., 1997.) Atthe same time, speakers did mention the “that”in sentence-complement structures withembedded-clause-biased verbs less than in sen-tence-complement structures with direct-object-biased (or neither-biased) verbs. Together, theseobservations suggest that speakers mention the“that” in sentence-complement structures atdifferent rates as a function of the bias of themain verb not because of any estimate of how dif-ficult the sentence will be for their comprehenders(in terms of a garden-path effect), but ratherbecause of how difficult it is to produce that sen-tence structure continuation given that verb.Verbs that are more frequently produced in sen-tence-complement structures are presumably pro-duced more easily in such structures, and sospeakers mention the “that” in them less; verbsthat are less frequently produced in sentence-comp-lement structures are presumably produced withmore difficulty in such structures, and so speakersmention the “that” in them more.

GENERAL DISCUSSION

Two main points follow from the currentexperiments:

1. Speakers say the “that”more in sentence-comp-lement structures with direct-object-biasedverbs than in sentence-complement structureswith embedded-clause-biased verbs. This con-firms offline results reported in Garnsey et al.(1997) and corpus results reported by Jaeger(2010).

2. However, themention of the “that” is not sensitiveto how often the main verb in a sentence-comp-lement structure appears with a direct object.Neither-biased verbs—verbs that do not oftenappear with direct objects—nonetheless are pro-duced in sentence-complement structures rela-tively often with the “that”. Rather, what seemsto influence “that” mention is how rarely speakersproduce sentences with particular verbs as sen-tence-complement structures; the less a main



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verb tends to appear with an embedded clause, themore likely speakers are to say the “that”.

Implications for how speakers communicatesuccessfully

The observation that speakers do not avoid produ-cing garden paths more in sentences where thatgarden path would be more disruptive (in thosewith direct-object-biased verbs) fits with otherresults in the literature. V. S. Ferreira and Dell(2000) reported that speakers do not say the“that”more in recalled sentence-complement struc-tures with embedded subjects that could beinterpreted as direct objects (and so permittedgarden-path interpretations) than in sentenceswith embedded subjects that could only be inter-preted as embedded subjects (and so did notpermit a garden-path interpretation; e.g., “Thecoach knew (that) you . . . ” vs. “The coach knew(that) I . . . ”). V. S. Ferreira (2006) reported asimilar result, but in written production and whenwriters were given specific instructions to write sen-tences that were as easy to understand aspossible. V. S. Ferreira and Hudson (2011) alsoshowed a similar effect, but in relatively naturalisticinteractive dialogue. Arnold, Wasow, Asudeh, andAlrenga (2004) showed that speakers do not avoidgarden paths in a different structure—namely, aprepositional dative (e.g., “The foundation gaveGrant’s letters to Lincoln to a museum inPhiladelphia”). Kraljic and Brennan (2005)showed that speakers do not disambiguategarden-path sentences with prosody any more inambiguous situations than in unambiguous situ-ations. And Snedeker and Trueswell (2003)showed that only speakers who were consciouslyaware of a potential garden path used prosody toavoid that garden path more in ambiguous situ-ations than in unambiguous situations. Tworesults suggest speakers do avoid garden paths:Temperley (2003) and Haywood, Pickering, andBranigan (2005). It may be that other confoundingfactors were responsible for the effects in theseexperiments, or that the effects may not beespecially robust (Roland, Dick, & Elman, 2007).It also may be that especially long (and so

potentially disruptive) ambiguities are at leastweakly avoided (Jaeger, 2010). At the very least,the bulk of evidence suggests that speakers do notgenerally avoid garden-path sentences.

The current evidence goes beyond previousresults in one important way, however. In previousdemonstrations, the difference between the garden-path and non-garden-path situations hinged onfeatures of the specific sentences that speakers pro-duced or the specific context in which the pro-duction was situated. For example, to say the“that” more in sentence-complement structuresbeginning “The coach knew (that) you . . . ” thanin those beginning “The coach knew (that)I . . . ”, speakers must recognize that a particularnoun phrase (“you”) is ambiguous in just the waythat allows a garden path in the to-be-producedsentence-complement structure, and that anotherpronoun (“I”) is not. This requires that speakersdetermine online as they produce the sentencethat it may or may not include a garden path.Here, no such online determination was necessary.In principle, speakers could build into their“offline” lexicalized grammatical knowledge a biasto say the “that” more in sentence-complementstructures that are generally more disruptive—those that are often followed by direct objects.Still, even a sensitivity to comprehension difficultythat speakers could represent in a (relatively) staticacross-the-board way does not seem to guidespeaker behaviour.

These results fit with the idea that there is adivision of labour for communicative success(V. S. Ferreira, 2008; see also Clark & Wilkes-Gibbs, 1986, for the notion of minimal collabora-tive effort). By this account, speakers in generaldo not produce sentences that are designed to beas easy to understand as possible (for example, byavoiding garden paths) because to do so is beyondthe speakers’ responsibility. The time and effortspeakers probably require to try to craft optimallycomprehensible utterances may simply be toocostly. Instead, speakers are responsible for produ-cing utterances that will convey their meanings suf-ficiently—even if they are not optimal forsubsequent comprehension—and to do so withsome dispatch. If a speaker’s addressee has some



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difficulty comprehending the sentence, communi-cation will probably still succeed well enough(F. Ferreira & Patson, 2007). If the addressee hasexcessive difficulty, she or he can interrupt the con-versation, request clarification, and so forth. Thecurrent results extend this framework by showingthat the relatively static biases speakers mighthave that guide sentence production also do notreflect comprehension sensitivity, at least asinduced by garden-path sentences. By this view,overall, speakers and their production biases guidethe production process; the subsequent compre-hension process does not.

It is worth noting that when consideringwhether speakers choose sentence features (e.g.,the “that”) to formulate easier to understand sen-tences, the current work (as well as much researchin the literature) has focused on garden-path-typeeffects. It may be that speakers’ production behav-iour might be sensitive to other factors that disruptcomprehension, especially if the disruptivenesscould exceed that precipitated by garden paths (asjust noted). Generalization of the notion of a div-ision of labour beyond ambiguity would bevaluable.

Non-retrieval-based influences on “that”mention

One other novel implication follows from thecurrent results. Previous demonstrations thatspeakers produce the “that” more in harder toproduce sentences have largely examined factorsthat reflect how easy or hard it is to retrieve sen-tence content (e.g., whether words repeat orwhether proactive interference is greater, asreviewed in the introduction here). The currentresults suggest that difficulty as measured bygreater “that” mention can also come from speak-ers’ past experience—in particular, how often theyhave produced particular structures with particularverbs. This is consistent with corpus studies onsyntactic production in spontaneous speech(Jaeger, 2006, 2010; Levy & Jaeger, 2007;Resnik, 1996), as well as analyses of /t/ and /d/deletion and prosodic reduction (Gahl &Garnsey, 2004). This shows that the production

of sentence structure might be sensitive to fre-quency in the same way as, say, the productionof individual words (Oldfield & Wingfield,1964). This fits well with approaches to pro-duction that view everyday language use asshaping speakers’ knowledge of the features oftheir language (Chang, 2002; Chang, Dell, &Bock, 2006; Chang, Dell, Bock, & Griffin, 2000).

The current results—including that neither-biased verbs were produced with “that” more—are also consistent with claims of how uniforminformation density influences language pro-duction (Jaeger, 2010). In terms of cognitivemechanism, greater frequency probably yieldseasier production. But in terms of mechanism-independent information, greater relative fre-quency of a syntactic structure corresponds toless informativeness from that syntactic structure.Indeed, the two accounts can be seen as differentlevels of description of the same sort of phenom-enon. Uniform information density is a compu-tational-level explanation that characterizes thedesign of certain classes of effects in sentence pro-duction. The effects of frequency observed here orretrievability in previous work can be seen as howcognitive mechanisms implement such a compu-tational account.

CONCLUSIONS

In principle, speakers’ sentence choices mightreflect a goal of being more easily understood, orthey might reflect the ease or difficulty they hadformulating sentences. Past research suggests thatspeakers do not choose one structure over anotherbecause they can assess online that that structurewould be easier for their addressee to understand.The current research takes this further and showsthat speakers do not choose one structure overanother because they have encoded in their gram-matical knowledge that the chosen structure tendsto be easier for addressees. Instead, speakers havethe responsibility of managing their own pro-duction burdens, so that they can say utterancesefficiently. If their grammar offers some flexibilityin the choice of an utterance on a particular



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occasion, they use that flexibility to promote thatefficiency.

Original manuscript received 16 November 2010Accepted revision received 13 November 2012

First published online 7 January 2013

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