Memory & Cognition1976, Vol. 4 (3), 283-290

Understanding sentences with relative clauses

DAVIn T. HAKES. JUDITH S. EVANS and LINDA L. BRANNONUniversity of Texas. Austin, Texas 78712

Sentences containing self-embedded relative clauses are generally believed to be difficult to understandbecause such clauses interrupt the clauses in which they are embedded. However. the experiments thatpurport to have demonstrated this have confounded the self-embedded or right-branching location of therelative clauses with their internal structure, comparing self-embedded object relatives withright-branching subject relatives. In order to break this confounding. Experiment I compared thecomprehension difficulty of self-embedded arid right-branching object relative clauses on two measures ofcomprehension difficulty. Experiment II made the same self-embedded vs. right-branching comparisonfor subject relative clauses. The results of both experiments consistently failed to support theinterruption hypothesis.

During the past decade, sentences with self-embeddedrelative clauses like Sentence 1, taken from Miller and!sard (1964), have received considerable attention fromlinguists and psycholinguists alike.

The prize that the ring that the jeweler that theman that she liked visited made won was givenat the fair. (1)

Such sentences are generally regarded as being extremelydifficult to comprehend, even though grammatical,and much research has been devoted to demonstratingthat they are more difficult to understand than othersentences of comparable semantic complexity butdifferent structure, Le., that there is a special difficultyinvolved in understanding self-embedded sentences.

Miller and Isard (1964), for example, studied thefree recall of sentences of constant length but varyingnumbers of self-embedded relative clauses, fmding thatrecall tended to become worse as the number of self­embeddings increased. Blumenthal (1966) found thatsubjects often paraphrased sentences with multipleself-embeddings incorrectly; and Stolz (1967) foundthat only after considerable practice could subjectsinterpret such sentences correctly. Foss and Lynch(1969) and Hakes and Foss (1970) showed that on-linecomprehension difficulty, measured by the phonememonitor task, was greater for doubly self-embeddedsentences than for right-branching sentences. And morerecently, Blaubergs and Braine (1974) have reportedthat in a short-term memory probe task sentences withthree or more levels of self-embedding were retainedmore poorly than comparable right-branching sentences.

Given the evidence of these and numerous other

This research was supported by Grant OEG-0-72-3941 fromthe National Institute of Education. The authors wish to thankDonald J. Foss for his comments. Author Brannon is now atMcNeese State University. Lake Charles, Louisiana 70601.

studies, there seems little doubt that self-embeddedsentences are difficult to understand and, in particular,more difficult than synonymous right-branchingsentences. The question is how best to account for thisdifficulty.

The "standard" account is one proposed by Millerand his co-workers (see, e.g., Miller & Chomsky, 1963;Miller & Isard, 1964), based on the observation thatself-embedded sentences like Sentence 1 are moredifficult to understand than right-branching sentenceslike Sentence 2 that have the same number of relativeclauses, and based also on formal considerationsconcerning how a sentence comprehension device mightoperate that made only a single left-to-right pass througha sentence.

She liked the man that visited the jeweler thatmade the ring that won the prize that was givenat the fair. (2)

Miller noted that each relative clause in a self-embeddedsentence interrupts the clause in which it is embedded,something not true in a right-branching sentence. Heproposed, essentially, that in comprehending a self­embedded sentence the processing of the main clausemust be interrupted between the subject and predicatein order to process the first relative clause; processingof that clause must, in turn, be interrupted to processthe second relative clause, and so on for as many clausesas are embedded. Assuming a limited capacity short­term processing memory that holds partially analyzedparts of clauses until their completions are available,Miller argued that more than a few self-embeddingswould overload the memory, resulting in comprehen­sion difficulty and/or failure.

Since Miller proposed the "interruption" hypothesis,it has achieved nearly the status of a received truth,and its validity has rarely been challenged. Further,

283

284 HAKES, EVANS, AND BRANNON

it seems to be equally widely accepted that the diffi­culty function for self-embedded sentences is discon­tinuous. One level of self-embedding is generallybelieved to cause little or no difficulty, while two ormore levels cause considerable difficulty (see, e.g.,Miller & Chomsky, 1963).

Miller and Chomsky appear to have suggested sucha discontinuity on the basis of informal intuitions;and it does seem intuitively clear that increasing thenumber of self-embedded clauses does increase diffi­culty and the likelihood of comprehension failure.But intuitions about difficulty seem to reflect mostdirectly on the number of self-embeddings necessary tocause comprehension failure, and it seems clear thatdifficulty can vary considerably before reaching a levelwhere it results in complete failure.

The results of Miller and Isard's study have oftenbeen taken as suggesting a difficulty discontinuitybetween one and two levels of self-embedding. Theseauthors do note that across successive recall trials"the performance curves for zero and one degree ofself-embedding are quite close, as are the curves forthree and four embeddings, with performance on thedoubly embedded sentence falling somewhere inbetween." But they present no analysis which would.support the conclusion that the difficulty differencebetween one and two embeddings is significantly greaterthan that between zero and one. In any event, theirdata concern multiple.trial free recall; and there is noparticular reason to believe that verbatim recall isrelated in any simple way to comprehensibility. Inaddition, as we will indicate below, all between­condition comparisons in this experiment are con­founded, with the result that their interpretation mustbe unclear. .

We suggest, then, that there is little empirical reasonto believe that comprehension difficulty increasesdiscontinuously with the number of embeddings.Further, we note in passing that different estimates ofwhere the discontinuity occurs do not agree. Conven­tional wisdom has it that the discontinuity occursbetween one and two embeddings; Blaubergs andBraine, on the other hand, report a discontinuity intheir probe recall data between two and threeembeddings.

Our concern here is not to question the conventionalwisdom that self-embedded sentences are difficult tounderstand. They are. Our concern is, rather, to questionwhether the interruption hypothesis accounts for thatdifficulty.

In comparing self-embedded sentences with right­branching sentences, there is, as Miller noted, adifference in the location of the relative clauses. In theformer, each relative clause modifies the subject of theclause that dominates it, separating the subject of thatclause from the predicate. In the latter, each relative

clause modifies the object of the dominating clauseand occurs after that clause's predicate.

However, for the self-embedded and right-branchingsentences that have been used in all the pertinent experi­ments there is an additional difference. These typesof sentences have differed in the internal structure ofthe relative clauses used, a difference that has beencompletely confounded with the self-embedded vs.right-branching difference. The relatives used in the self­embedded sentences have been object relatives, onesin which the direct object of the clause has been frontedand relativized. Those used in the right·branchingsentences, however, have been subject relatives, onesin which the subject of the relative clause has beenrelativized. Given this confounding of a difference inrelative clause location with a difference in the internalstructure of the relatives, it is entirely possible that theresults of all the pertinent experiments could be attri­buted to the internal structure difference rather thanto the difference between self-embedded and right­branching locations.

Thus an unbiased evaluation of the interruptionhypothesis requires breaking the confounding that hasbeen present in previous studies of the difficulty ofself-embedding. This could be accomplished in eitherof two ways: (I) holding the internal structure of therelative clauses constant while varying their location,or (2) holding their location constant while varying theirinternal structure. The first of these is the more directtest of the interruption hypothesis, and we have chosenit for that reason. Experiment I examines the self­embedded vs. right-branching difference using objectrelative clauses; Experiment II examines the samedifference using subject relative clauses.

One problem associated with this approach is thatthe sentences used in the two conditions of eachexperiment cannot be synonymous. This, of course,is a common problem in research on sentence compre­hension, for it is generally the case that differences instructure are associated with differences in meaning.In fact, some of the earlier, confounded studies ofself-embedding and right-branching allowed meaningto vary between conditions (see, e.g., Foss & Lynch,1969). We have attempted to minimize the possibleinfluence of such semantic differences in waysdescribed below.

A second problem is more apparent than real. As wehave noted earlier, it is generally believed that thedifficulty of self-embedded sentences increases discon­tinuously with the number of such embeddings. Eventhough there is scant evidence for such a discontinuity,it is clear that difficulty does increase with the numberof such embeddings. For this reason, the strongestcomparison of self-embedded and right-branchingsentences would be between sentences with severalobject relative clauses occurring in self-embedded

UNDERSTANDING SENTENCES WITH RELATIVE CLAUSES 285

position and sentences with the same number of objectrelatives in right-branching position (or, alternatively,between sentences with several self-embedded subjectrelatives and ones with an equal number of right­branching subject relatives).

Such a comparison is, however, impossible inprinciple. Sentence 3 contains a single right-branchedobject relative clause.

The girl hated the teacher that the boyliked. (3)

Since that clause is verb final, there is no way in whichthat clause can be modified by another relative clausewithout its being interrupted, Le., without the secondclause being embedded within the first. A similarproblem arises when using subject relative clauses,though here the difficulty occurs when such clausesare self-embedded rather than right-branched. Attempt­ing to construct the relevant examples should quicklyconvince the reader.

The result of this is that the comparison must bebetween one level of self-embedding and zero, betweentwo levels and one, etc. As we have indicated earlier,conventional wisdom to the contrary, there is no com­pelling reason to believe that the difficulty differencebetween two levels of self-embedding and one is anygreater than the difference between one level and zero,so we have chosen the latter comparison to examine.

It does seem possible, however, that a differencein comprehension difficulty between self-embeddedand right-branching sentences involving only singlerelative clauses might not become apparent unless theoverall level of comprehension difficulty is relativelyhigh. For this reason, another variable-relative clausereduction-was included in both experiments. Fodorand Garrett (1967) have shown that omitting the relativepronouns from doubly self-embedded sentences resultsin their being even more difficult to comprehend.Hakes and Cairns (1970) and Hakes and Foss (1970)have shown that this reduction also significantly affectsperformance on an on-line measure of comprehensiondifficulty, the phoneme monitor task. For this reason,each sentence in each experiment was presented withits relative clause either reduced or unreduced.

To assess comprehension difficulty, we chose twotasks: paraphrasing and phoneme monitoring. The firstof these provides a postsentential measure of compre­hension difficulty. The second requires that the subject,while trying to understand a sentence presented audi­torily, listen in the sentence for a word beginning witha specified target phoneme and, if the target occurs,respond to it as quickly as possible. A number ofexperiments have shown reaction time in this taskto be a sensitive measure of on-line comprehensiondifficulty attributable to sentence structure (e.g., Foss

& Lynch, 1969; Hakes & Cairns, 1970; Hakes & Foss,1970; Hakes, 1972), to ambiguity (e.g., Foss, 1970;Foss & Jenkins, 1973; Swinney, 1974), and to a varietyof other variables that have been hypothesized toaffect comprehension difficulty.

Use of two comprehension difficulty measures allowsus to test two aspects of the interruption hypothesis.First, that hypothesis predicts that sentences contain­ing self-embedded relatives will be more difficult tocomprehend than one containing right-branchingrelatives; such a difference should appear in a globalmeasure of difficulty such as the paraphrasing task.Second, the hypothesis predicts that the difficultydifference between self-embedded and right-branchingrelatives should first manifest itself within the relativeclauses themselves, for it is just the necessity of holdinginformation about the interrupted embedding clausethat is claimed to cause the greater difficulty of theformer. Thus, measuring phoneme monitoring latencyto targets within the relative clauses provides a test ofwhether a difficulty difference arises where a hypothe­sis predicts.

EXPERIMENT I

MethodDesign and materials. Twenty sentences were constructed,

each of which contained a single object relative clause whichcould modify either the subject (self-embedded) or object(right-branching) of the sentence's main clause, e.g.,Sentence 4. The subject and object NPs of each sentence'smain clause were interchangeable.

After the fmal curtain on opening night, the director(that) the repertory company had hired praised thestar performer. (4a)

After the final curtain on opening night, the star per­former praised the director (that) the repertory companyhad hired. (4b)

Thus, the content of the relative clause was the same, as wasthe NP it modified, regardless of whether it modified the subjector the object of the main clause.

Since each sentence could be presented with its relativeClause either reduced or unreduced and with the relative clausemodifying either the subject or object of the main clause, therewere four versions of each sentence. The sentences were allcomplex in ways additional to the relative clauses, containingother main and subordinate clauses and/or complex modifiers.

Each sentence was constructed so that a word within therelative clause contained the target phoneme for monitoring.This was either the subject noun of the relative or a prenominaladjective modifying that noun. Thus, in Sentence 4 the targetphoneme was the /r/ in repertory. The particular phoneme thatserved as the target varied across sentences, but in the sentencein which it was the target, it did not occur elsewhere in word­initial position.

Twenty-eight filler sentences were also constructed, each ofa degree of complexity comparable to that of the test sentences,but without any particular structural constraints observed intheir construction. Of these, 15 contained monitoring targets,located at widely varying points and occurring in diverse types

286 HAKES, EVANS, AND BRANNON

Table IPhoneme Monitoring Speed and Paraphrasing

Accuracy: Experiment I

of words. The remanung 13 filler sentences contained nomonitoring targets and were included to prevent the subjects'expecting such a target to occur in every sentence.

There was thus a total of 48 sentences, 20 of which con­tained object relative clauses. A single quasi-random orderof the 48 sentences was constructed, and four tape record­ings of the sentences in this order were made. The 20 testsentences were randomly divided into four sets of five sentenceseach. On anyone tape, one set occurred in each of the fourpossible combinations of relative clause location (self-embeddedvs. right-branching) and relative clause reduction (reduced vs.unreduced). The assignment of test sentence versions of tapeswas by an ordered roll-<>ver technique.

Tones of 1,000 Hz were recorded on a separate track ofeach tape, inaudible to the subjects and coincident with theonset of each target phoneme. These were used to start the .timer used to measure monitoring latency. Each sentence waspreceded on each tape by an instruction specifying the targetphoneme for that sentence. For the filler sentences not con­taining monitoring targets, the instruction was to listen for aphoneme that did not occur in word-initial position anywhere inthat sentence. Instructions for the phoneme monitor and para­phrase tasks and four practice sentences were also recorded anddubbed onto the beginning of each of the four tapes.

To summarize, the design included four groups, defmed bythe four tapes, Le., by the assignment of test sentences toconditions. Within subjects, there were two values of eachof two variables: relative clause location (self-embedded vs.right-branching) and relative clause reduction (reduced vs.unreduced). The design was thus a 4 by 2 by 2 mixed factorial.

Procedure. Subjects were assigned to groups randomly;all were tested individually by the same experimenter. Theinstructions and sentences were presented binaurally throughheadphones at a comfortable listening level. The general instruc­tions indicated that the subject was to try to comprehend eachsentence and was to: (a) listen for a word in each sentencebeginning with the sound specified by the instruction precedingthat sentence; (b) respond by pressing a button as quickly aspossible if such a word was heard; and (c) say in his own words,after the sentence was fmished, what the sentence meant. Theinstructions explicitly discouraged verbatim repetition of thesentences, and, if necessary, subjects were further instructedon this point following the practice sentences. The four practicesentences were then presented, followed by the 48 test and fillersentences. The button used for the monitoring response wasmounted on a panel angled toward the subject at 30 deg abovethe horizontal plane. Subjects responded with whichever digitthey preferred. Paraphrase responses were made orally and taperecorded for later analysis.

SUbjects. Forty students from the freshman-level introduc­tory psychology course at the University of Texas at Austinserved as subjects. Participation in experiments was a courserequirement, but the subjects were not required to participatein this particular experiment. All were native speakers of English,

Monitoring Paraphrasing .Speed AccuracyCondition

Self-EmbeddedUnreducedReduced

Right-BranchingUnreducedReduced

1.9971.811

1.9341.720

.451

.514

.409

.460

and none had previously served in any experiment on sentencecomprehension. Approximately equal numbers of males andfemales served, though subjects were neither selected norassigned to groups on this basis.

Results and DiscussionPhoneme monitoring. Individual trial monitoring

latencies were converted to speed scores by reciprocaltransformation. For each subject, four mean speedscores were computed, one for the sentences of eachof the four conditions. The means of these mean speedscores, taken across groups, are presented in Table 1 andindicate that monitoring was faster when the relativeclauses were se!f-cmbedded than when they were right­branching. Further, as anticipated, monitoring wasfaster when the relative clauses were unreduced thanwhen they were reduced.

The mean speed scores were subjected to a Groupsby Self-Embedded vs. Right-Branching by Reduced vs.Unreduced analysis of variance. The main effect forSelf-Embedded vs. Right-Branching was significant,F(l,36) =5.499, p < .05, MSe =.437, as was the maineffect for Reduced vs. Unreduced, F(l,36) = 24.617,P < .001, MSe =.652. The main effect for Groups wasfar from significant, F < I, and no interactionsapproached significance.

The effect attributable to relative clause reductionindicates that omitting the relative pronouns from objectrelative clauses substantially increased on-line processingdifficulty even when the sentences upon which thisvariation was worked were less complex than the doublyself·embedded sentences used in earlier experiments.

The effect of main interest is, of course, that attribut­able to the self-embedded or right-branching locationof the relative clauses, for the interruption hypothesisclearly predicts that monitoring should be slower forself-embedded clauses than for right-branching clauses.The results indicate, however, that monitoring wasfaster for the self-embedded clauses. The effect is smallin magnitude, and, to determine its reliability, a secondanalysis was performed. Here the data were analyzedsentence by sentence, with the speed scores collapsedacross groups. The effect for the Self-Embedded vs.Right.Branching comparison was marginally significant(.05 < p < .1 0, two-tailed Wilcoxon matched pairs,signed-ranks test). (The effect for the Reduced vs. Unre­duced comparison was highly significant, p < .01.)Thus, whether analyzed by subject or by sentence,the results show much the same effect: Sentences withself-embedded object relative clauses yield marginallyfaster phoneme monitoring latencies than sentenceswith right-branching object relative clauses. However,whether this is a reliable effect or not is of only minorinterest; for, even it if is not, the results are in thedirection opposite to that predicted by the interruptionhypothesis. Hence, there is no way these results can beinterpreted as lending aid or comfort to that hypothesis.

UNDERSTANDING SENTENCES WITH RELATIVE CLAUSES 287

Paraphrasing. Each test sentence was divided intosegments corresponding roughly to surface structureclauses, there being either three or four such segmentsper sentence. The paraphrase responses were scored onthe basis of the number of such segments accuratelyrepresented in the response. To be scored correct, boththe internal grammatical relations of a segment and thatsegment's relations to the sentence's other segmentshad to be represented accurately. Lexical substitutionwas liberally allowed, except for the substitution of anindefinite term for a defmite one (e.g., someone forthe director). Verbatim repetitions of a sentence werenot credited.

Each paraphrase response was transcribed and wasscored independently by two judges. Each judge scoredall paraphrases of all versions of a given test sentencebefore proceeding to the next sentence. Differencesin the scores assigned by the two judges were resolvedby discussion (sometimes acrimonious) after all scoringwas completed.

Since the number of segments scored varied acrosssentences, a subject's accuracy score was taken as theproportion of the sentence's segments paraphrasedaccurately. Four mean accuracy scores were then com­puted for each subject, taking the mean proportioncorrect across the sentences in each of the four condi­tions. The means of the mean accuracy scores, takenacross groups, were presented in Table 1.

The mean accuracy scores were subjected to an analy­sis of variance. The main effect for Self-Embedded vs.Right-Branching was highly significant, F(l ,36) = 7.653,P < .01, MSe = .120. The effect here is thus consistentwith that obtained for monitoring latency: Accuracy isgreater for self-embedded object relatives than for right­branching object relatives. Again, the effect is just theopposite of that predicted by the interruptionhypothesis.

The main effect for Relative Clause Reduction was alsohighly significant, F(l,36) = 10.067, P < .01, MSe =

.128. But, paradoxically, the effect was in the wrongdirection: Paraphrasing was better when the relativeswere reduced than when they were not. This result isconsistent neither with the results obtained here forphoneme monitoring nor with previous paraphrasingresults. The interaction of Relative Clause Reduction withSelf-Embedded vs. Right-Branching location was notsignificant, F < I. The only other effect to reach signifi­cance was the Groups by Reduced vs. Unreduced inter­action, F(3,36) =7.630, p< .01,MSe =.128, indicatingthat, for one assignment of test sentences to conditions,paraphrasing was more accurate for the unreducedrelatives while, for the other three assignments, para­phrasing was more accurate for the reduced relatives.

To investigate further the reliability of these effects,the paraphrasing accuracy data were also subjected toa sentence-by-sentence analysis. Here the effect for self­embedded vs. right-branching, although in the same

direction as in the analysis by subjects, was not signifi­cant (p> .05); the effect for reduced vs. unreduced wassignificant (p < .05), both by two·tailed Wilcoxon tests.

In summary, then, the results for both tasks areconsistent in indicating that comprehension difficultyis no greater for sentences containing self-embeddedobject relatives than for sentences containing right­branching object relatives. Whether difficulty is actuallyless for the self-embedded sentences is not entirelyclear. But, since the interruption hypothesis clearlyrequires it to be greater, even a nonsignificant effectin the wrong direction is sufficient to disconfirm thathypothesis. The conventional wisdom that self­embedded sentences are more difficult to understandthan almost anything else (including right-branchingsentences) is clearly not supported.

.EXPERIMENT n

Experiment I has demonstrated that, for objectrelatives, interruption of the dominating clause doesnot result in increased comprehension difficulty, thusdisconfirming the interruption hypothesis. But thathypothesis does not apply just to object relatives. Itclaims, rather, that interruption of a dominating clauseshould result in increased comprehension difficultyregardless of the nature of the embedded clause. Thusthe interruption hypothesis predicts the same outcomeconcerning self-embedded or right-branching clauselocations for subject relatives as it did for objectrelatives: Self-embedded subject relatives should resultin greater comprehension difficulty than the samerelatives in right-branching location.

Experiment II tested this prediction, comparingsentences containing subject relatives in either self­embedded or right-branching location.

MethodDesign and materials. The materials here paralleled those of

Experiment I as nearly as possible, the exception being theinternal structure of the relative clauses used. Again, 20 testsentences were constructed, each of which contained a singlesubject relative that could modify either the subject or the directobject of the sentence's main clause, e.g., Sentence 5.

The children (that were) playing in the hayloftstartled the farmer's wife when she went to gatherthe eggs. (Sa)

The farmer's wife startled the children (that were)playing in the hayloft when she went to gatherthe eggs. (5b)

Whenever possible, the sentences of Experiment I were used,modified in the appropriate way.

The verb in the reIa tive clause was always in the past progres­sive tense, allowing us to present the sentences with the relativeclauses either reduced or unreduced. There is a general rule ofEnglish syntax which prohibits reducing a subject relative if itsmain verb is nonprogressive. One reason for this appears to bethat, when such a relative clause is reduced, the fact of its

288 HAKES, EVANS, AND BRANNON

Table 2Phoneme Monitoring Speed and Paraphrasing

Accuracy: Experiment II

existence is obscured, making miscomprehension likely (seeBever & Langendoen, 1971).

The filler sentences were identical to those of Experiment I,as were all details of tape construction and the placement oftones for phoneme monitoring. The monitoring target for eachtest sentence was the initial phoneme of the head noun of therelative clause's direct object. Here, as in Experiment 1, therewere four groups of subjects, defmed by the assignment of testsentences to the self-embedded and right-branching conditionsand the reduced and unreduced conditions. Within subjects,these four conditions were combined orthogonally.

Procedure. The procedure was identical in all respects to thatof Experiment I.

Subjects. Forty subjects, having the same general character­istics as those used in Experiment I, participated. Ten wereassigned to each group according to a quasi-random schedule.

Results and DiscussionPhoneme monitoring. Reduction of the monitoring

data to mean speed scores was accomplished in the samemanner as in Experiment I, with one exception. Afterdata collection was completed, it was discovered thatone test sentence had inadvertently been misrecordedon one tape. Data for this sentence were eliminated forall groups, with the resul~ that the mean speed scores forthe conditions into which that sentence entered werebased on one fewer latency than the other conditions.The means of these mean speed scores, taken acrossgroups, are presented in Table 2.

Ove-.:all, responding here was rather faster than inExperiment I. This suggests that the subject relativescaused less comprehension difficulty than the objectrelatives, though it might also reflect other differencesbetween the sentences of the two experiments, e.g.,the difference in monitor target location. The differencebetween the self-embedded and right-branchingconditions is in the same direction as in Experiment I,monitoring being slightly faster when the relatives wereself-embedded. The effect is, however, far smaller thanthat obtained with object relatives. Monitoring was alsoslightly faster when the relatives were reduced thanwhen they were unreduced, but again the effect isminiscule.

Analysis of variance of the mean speed scores bearsout the impressions gained by inspection. The maineffects for Self-Embedded vs. Right-Branching and forReduced vs. Unreduced were both far from significant,F < I in both cases. The only effect to reach signifi-

Monitoring ParaphrasingSpeed Accuracy

cance was that attributable to the Groups by Self­Embedded vs. Right-Branching interaction, F(3,36) =3.880, p < .02, MSe = .067. In the absence of a signifi­cant main effect for Self-Embedded vs. Right-Branching,this is of little consequence.

As in Experiment I, the monitoring data here werealso analyzed sentence by sentence, with the speedscores collapsed across groups. The results werecompletely consistent with those obtained when thedata were analyzed by subject: Neither the Self­Embedded vs. Right-Branching comparison nor theReduced vs. Unreduced comparison approached signifi­cance. It is perhaps worth noting, however, that for theformer comparison the direction of the difference wasthe same as in the analysis by subjects: Monitoringtended to be faster when the relatives were self­embedded than when the same relatives were right­branching in the same sentences.

It appears, then, that no substantial difference inon-line processing load resulted either from a differencein the self-embedded or right-branching location of thesubject relatives or from whether they occurred incomplete form or with the relative pronouns andauxiliary verbs deleted. The fact that the processing loadwas not greater when the relatives were self-embeddedis, of course, inconsistent with the interruption hypothe­sis. Since no effects of interest were significant in themonitoring data for Experiment II, it might be arguedthat the design and/or materials used were not suf­ficiently sensitive to allow detection of a smalldifference of the sort predicted by the interruptionhypothesis. The fact that significant differences wereobtained using the same design in Experiment I (albeitnot the one predicted by that hypothesis) argues againstsuch a conclusion, as does the fact that, whetheranalyzed by sentence or by subject, the difference isin the wrong direction.

In addition, informal comparison of the presentresults with those of Experiment I suggests that subjectrelatives caused less on-line comprehension difficultythan object relatives, regardless of whether they wereself-embedded or right-branching, a point to which wewill return.

Paraphrasing. The paraphrasing data were treated ina manner identical to that described for Experiment I,with the same exception noted above for the phonememonitoring data for Experiment II. Again, two judgesindependently scored each paraphrase, using the sameprocedures and criteria as in Experiment I.

The paraphrasing data are presented in Table 2 interms of mean proportion accuracy scores, taken acrossgroups, for the four conditions. The overall level ofaccuracy is considerably higher than that found inExperiment I for sentences containing object relatives,again suggesting that subject relatives cause less compre­hension difficulty than object relatives. Accuracyappears to have been somewhat higher for subject rela-

.679

.646

.625

.628

1.9892.021

2.0091.984

Condition

Self-EmbeddedUnreducedReduced

Right-BranchingUnreducedReduced

UNDERSTANDING SENTENCES WITH RELATIVE CLAUSES 289

tives that were self-embedded than for the same relativeswhen they were right-branching, and also somewhatgreater when the relatives were unreduced than whenthey were reduced.

Analysis of variance of the paraphrasing data revealedthat the main effect for Self-Embedded vs. Right­Branching was significant, F(l,36) = 4.503, p < .05,MSe = .012. The main effect for Reduction was notsignificant, F < 1. Somewhat complicating the interpre­tation of these results is the fact that the main effectfor Groups was significant, F(3,36) = 3.133, p < .05,MSe = .086, as were the interactions of Groups by Self­Embedded vs. Right-Branching, F(3,36) =9.463, p <.001, MSe = .012, and Groups by Self-Embedded vs.Right-Branching by Reduction, F(3,36) = 3.126, P <.05, MSe .014. Inspection of the data suggests that theseeffects are primarily attributable to atypically lowaccuracy (.42) for one group of subjects for thesentences with reduced relatives in self-embeddedlocation. Performance for that set of sentences underother conditions for other groups of subjects was notatypical, suggesting that the cause of the atypicalperformance in that one cell was not the sentencesthemselves. However, the subjects in the group con­tributing the atypical performance tended to be lessaccurate for all conditions than the subjects in the othergroups, suggesting that it was the subjects that wereatypical. Inspection of the phoneme monitoring datafailed to yield any evidence of unusual performance forthis group.

To check on the consistency of the effects obtainedin this analysis, the paraphrase data were also analyzedby sentence in the manner described for Experiment I.Sentences with self-embedded subject relatives wereparaphrased significantly more accurately than sentenceswith right-branching subject relatives (p < .05, two­tailed Wilcoxon test). The difference favoring greaterparaphrasing accuracy for sentences with unreducedrelatives was marginally significant (.05 < P < .1 0,two-tailed Wilcoxon test). Thus, the effect for relativeclause location appears consistent across test sentences;and the reduction effect which was masked in thesubject analysis by the presence of two significantinteractions may be a real, though small, effect.

The paraphrasing data are, then, consistent with themonitoring data in showing no consistent effect forrelative clause reduction. While there is some sugges­tion that such an effect exists and is being masked, itseems clear that it is not an effect of major import­ance. The paraphrasing data do, however, reveal asignificant difference between self-embedded and right­branching subject relatives that was not apparent in themonitoring data. Finally, the overall levels of para­phrasing accuracy for the two experiments suggest,as do the phoneme monitoring latencies for the two,that subject relatives cause less comprehension diffi­culty than do object relatives.

It is somewhat problematic that the paraphrasingand phoneme monitoring data for this experiment arenot consistent: For the former, self-embedded relativescaused significantly less comprehension difficulty thanright-branching, while, for the latter, the difference wasnot significant. It should, of course, be borne in mindthat the discrepancy here concerns only whether self­embedded subject relatives are easier to process thanright-branching ones or whether there is no difference;in neither case is there any suggestion that self­embedded clauses are harder to process.

We have no account of the difference in which wehave any confidence. It does seem possible that for thesentences in question the monitoring targets werelocated at points at which the processing load differedonly minimally and that locating them differently wouldhave yielded a larger difference. Alternatively, it ispossible that subject relatives, regardless of where theyare located, add little to the amount of on-line process­ing involved in initially comprehending a sentence. Ifso, the difference obtained with the paraphrase taskmight reflect some difference associated with theconstruction of paraphrases itself. The present data shedno light on which of these, or of the myriad otherpossibilities, might be correct.

GENERAL DISCUSSION

The relative clause reduction variable was includedin the present experiments mainly to increase the over­all comprehension difficulty of the sentences. We hadanticipated that difficulty differences between self­embedded and right-branching sentences might appearonly if overall difficulty was high. Clearly, this anticipa­tion was disconfirmed, for in neither experiment wasthere an interaction between reduction and the self­embedded vs. right-branching difference. Whateverdifferences in difficulty resulted from these two manipu­lations were quite independent.

The results of main interest are, of course, thoseconcerning the difference between self-embedded andright-branching relative clauses. The results seem clearand unambiguous: When the internal grammaticalstructure of the relatives is controlled, there is noevidence whatsoever that sentences containing self­embedded relatives are more difficult to comprehendthan ones containing right-branching relatives. There is,in fact, some suggestion that the latter are the moredifficult. Given the present evidence, the interruptionhypothesis cannot be correct.

However, a question remains. If sentences contain­ing self-embedded relatives are not more difficult tounderstand than ones containing right-branching rela­tives, then how are we to account for the results of allthose experiments that have concluded the contrary?Recall that in all of those experiments the comparisonwas between self-embedded objecf relatives and right-

290 HAKES, EVANS, AND BRANNON

branching subject relatives. If the greater difficulty ofthe former cannot be attributed to the fact of self­embedding, then it seems to follow logically that thedifficulty is attributable to the difference betweensubject and object relatives.

This conclusion would be more palatable if, inaddition to a logical argument, we could support itwith a direct empirical argument. Certainly, a compari­son of the results of Experiments I and II is suggestive,for it does appear that for both tasks object relativesare more disruptive of comprehension processing thanare subject relatives, regardless of whether those clausesare self-embedded or right-branching. We are, however,reluctant to place great confidence in such a between­experiments comparison. Neither the sentences nor themonitoring targets are directly comparable for thesentences of the two experiments. In addition, the datafor the two were collected from different subjects atdifferent times by different experimenters. We have,for these reasons, refrained from performing any statis­tical analysis of the between-experiments comparison.

We should note in closing, however, that Fodor,Bever, and Garrett (1974, see especially pp. 344-346)present an argument, together with some supportingdata, rationalizing the conclusion to which our experi- .ments seem to point: Object relative clauses are moredifficult to understand than subject relative clauses;all other things equal, self-embedded relatives are notmore difficult than right-branching relatives.

REFERENCES

BEVER. T. G.. & UNGENDOEN, D. T. A dynamic model of theevolution of language. Linguistic Inquiry, 1971, 2.433-404.

BLAUBERGS. M. S.. & BRAiNE. M. D. S. Short-term memory

limitations on decoding self-embedded sentences. Journal ofExperimental Psychology, 1974. 102. 745-748.

BLUMENTHAL. A. L. Observations with self-embedded sentences.Psychonomic Science, 1966,6,453454.

FODOR. J. A.. BEVER. T. G.. & GARRETT, M. F. The psychologyof language. New York: McGraw-Hili. 1974.

FODOR. J. A.,& GARRETT. M. Some syntactic determinants ofsentential complexity. Perception & Psychophysics, 1967.2.289-296.

Foss, D. J. Some effects of ambiguity upon sentence compre­hension. Journal of Verbal Learning and Verbal Behavior.1970.9.699-706.

Foss, D. J., & JENKINS, C. M. Some ellects of context on thecomprehension of ambiguous sentences. Journal of Verbal'Learning and Verbal Behavior. 1973, 12. 577-589.

Foss. D. J., & LYNCH, R. H., JR. Decision processes duringsentence comprehension: Effects of surface structure ondecision times. Perception & Psychophysics, 1%9,5, 145-158.

HAKES, D. T. Effects of reducing complement constructionson sentence comprehension. Journal of Verbal Learning andVerbal Behavior. 1972. II. 278-286.

HAKEs. D. T .. & CAIRNS. H. S. Sentence comprehension andrelative pronouns. Perception & Psychophysics. 1970. 8, 5-8.

HAKEs. D. T .. & Foss, D. J. Decision processes during sentencecomprehension: Effects of surface structure reconsidered.Perception & Psychophysics, 1970, 8.413-416.

MILLER. G. A.. & CHOMSKY. N. Finitary models of languageusers. In R. D. Luce. R. R. Bush. & E. Galanter (Eds.l.Handbook of mathematical psychology, Vol. ll. New York:Wiley. 1963. Pp. 419-492.

MILLER. G. A.. & !sARD, S. Free recall of self-embeddedEnglish sentences. Information and Control. 1904. 7. 292-303,

STOLZ. W. S. A study of the ability to decode grammaticallynovel sentences. Journal q( Verbal Learning and VerbalBehavior, 1%7. 6. 867-873,

SWINNEY, D. A. Effects of context upon the processing oflexical ambiguities during sentence comprehension,Unpublished PhD dissertation, University of Texas atAustin. 1974.

(Received for publication June 5. 1975:revision received October 13, 1975;

accepted October 20. 1975.)