Journal of Psycholinguistic Research, Vol. 26, No. 2, 1997

Research Note

Judgments of Processing Load in Japanese: TheEffect of NP-gra Sequences

Keiko Uehara1,2

This study reports an effect of more than two consecutive noun phrases (NPs) with thesame nominative case marker, -ga, on ratings of processability for Japanese multiplycenter-embedded sentences. The findings imply that the processing overload theory ofBabyonyshev and Gibson (1995) requires modification. Although that theory sets thecritical limit (beyond which parser breakdown occurs) at four processing load units(PLUs), it appears that the parser is overloaded by anything over five PLUs. where athree NP-ga sequence contributes roughly an additional PLU to processing cost. Theevidence also suggests that inherently cased NPs are not cost free.

Babyonyshev and Gibson (1995) (henceforth, B&G) proposed a theorywhich predicts processing load for multiply center-embedded sentences interms of two factors: The number of structurally cased noun phrases (NPs)[nominative (Nom), accusative (Ace), and genitive (Gen)] not yet assigned0 roles3; and the number of self-embeddings (SEs). A sentence is predicted

While I was pursuing this study, I was supported by many people. In particular, I wouldlike to acknowledge Dianne Bradley, Janet Dean Fodor, and Gita Martohardjono for theirvaluable comments and advice.1 The Graduate Center of The City University of New York, New York, New York

10036.2 Address all correspondence to Keiko Uehara, Ph.D. Program in Linguistics, The Grad-

uate School and University Center, The City University of New York, 33 West 42ndSt., New York, New York 10036-8099.

3 Under this theory inherently cased NPs are assumed not to contribute to processingload. That is, when an NP with inherent case is processed, information about the NP's6 role becomes available, and this information is sufficient for the NP to be treated asif it had received its 0 role.

0090-6905/97/0300-0255$ 12.50/0 © 1997 Plenum Publishing Corporation

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to be unprocessable when the accumulation of processing load units (PLUs)for its correct analysis exceeds four; the idea is that, over this limit, thereis a "processing overload" which leads to parser breakdown.

Native-speaker intuition suggests, however, that Japanese exhibits asource of processing difficulty in addition to those considered in B&G'stheory, a cost arising when more than two consecutive NPs bear the samenominative case marker, -ga. The exploratory study reported in this papersystematically examined the effect of such sequences on processing load,using an off-line judgment task. The critical contrasts of the experimentinvolved processability ratings for sentences constructed in minimal pairs:While one sentence contained three (or more) consecutive NP-ga's (hence-forth, 3ga), its counterpart avoided the 3ga sequence in one of a variety ofways. Systematic shifts in rated processability, worse for 3ga cases than fortheir otherwise comparable counterparts, would constitute evidence that suchNP-ga sequences, of themselves, are a source of processing difficulty. Whythis might be so is taken up after the report on the study.

METHOD

Subjects

Thirty-two native speakers of Japanese (average age 31 years, averagelength of stay in the U.S. 3;6 years, all with B.A. degrees from a Japanesecollege) participated voluntarily in the experiment, by completing a ques-tionnaire. Usually this took no more than 15 min.

Materials

The subjects were presented with a questionnaire in three sections,printed entirely in Japanese script. Section 1 sought basic demographic in-formation. Section 2 presented sentences singly, and asked for processabilityjudgments on a 6-point scale whose points were represented by symbolsfrequently used in the Japanese culture: At one end of the scale, symbols© and O were used to indicate sentences that were very easy to understandand understandable, respectively; and at the other, symbols X X and X in-dicated sentences that were impossible and difficult to understand, respec-tively. The crucial middle values, with symbols Q? and X?, allowed asubject to indicate the difference between a sentence that was understandable(though barely) and one that had led to processing overload. Finally, Sec. 3presented sentences in minimal pairs (a 3ga sentence and its counterpart,together), and asked for judgments of relative processability.4

4 Since the outcomes for Sec. 3's relative judgments replicated the findings reportedbelow, these data are not discussed here. See Uehara (1996).

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In order to investigate the effect of 3ga on processability, sentenceskeletons with 3ga were constructed; all were for structures accumulatingfive PLUs in B&G's metric, that is, exceeding the proposed processing loadlimit. These were then adapted to avoid the -ga sequence without changingeither sentence meaning or cost in PLUs, using the devices described below:

a. -ga/-no Conversion. Part of a 3ga sequence was replaced by an NPbearing the genitive case marker -no. In Japanese, -no (Gen) canmark not only a possesser of an NP but also the subject of a relativeclause or the head of a noun-complement clause (see, e.g., Miyagawa1994).

b. -ga/-wa Conversion. The first NP-ga of a 3ga sequence was topi-calized and thus marked by -wa. Since topicalization involves fewconstraints, three subtypes of -gal-wa conversion were tested, instructures which arrived at their five PLUs in different ways. Thefirst had four structurally cased NPs [three marked by -ga, one by-o (Ace)] and one SE, and the second had three structurally casedNPs (all marked by -ga) and two SEs. The third type, like the first,had four structurally cased NPs and one SE, but marked all NPswith -ga—in Japanese, certain verbs permit go-marked objects—sothat this third variety of -ga/-wa conversion contrasted the process-ability costs of 4ga versus 3ga sequences.

c. ADV insertion. A 3ga sequence was split up by inserting an adverb(ADV) after the second NP-ga. In the original 3ga sentence, thisadverb appeared in the same clause, but later, in association withthe verb.

Note that none of (a) through (c) affect the PLU count in B&G's theory,5though -gal-no conversion and topicalization are assumed to involve move-ment and would be predicted to add to processing cost in other parsingmodels (cf. the minimal chain principle of De Vincenzi, 1991).

From each of five basic skeletons, two sentences were created, differingonly in lexical content. These 10 sentences were then adapted as outlinedabove [two each for (a) and (c), and six for (b)]. The 20 test sentences weredistributed to form two counterbalanced versions of a questionnaire, so thatno subject saw any 3ga sentence and its adapted counterpart with the same

5 M. Babyonyshev, personal communication, February 1996.

Judgments of Processing Load in Japanese 257

lexical content. Table I presents sentence skeletons6; for a full list of testsentences, see Uehara (1996).

Beyond the mere fact of a systematic shift in rated processability, in-terpretation of test sentence data requires that the magnitude and endpointsof any observed shift be tied to scale points. That is, for data interpretationat a maximally informative level of detail, anchoring of scale values is re-quired. Section 2 of the questionnaire thus included four anchor sentences,constructed on the basis of B&G's theory. These were modeled on examplesin B&G's published work, except that 3ga sequences were avoided. Twoanchor sentences (AS1 and AS2) were designed to be processable (threePLUs); these differed in that one included two inherently cased NPs (bothNP-wj, Dat) (Dat-dative), which are associated with no additional PLU costin B&G's metric. The remaining two anchor sentences (ASS and AS4) weredesigned to be instances of processing overload, with counts of 5 PLUs and6 PLUs, respectively. Anchor sentences (see Appendix) appeared in identicalform in each version of the questionnaire.7

Procedure and Data Treatment

Subjects were requested to proceed through the questionnaire at theirown pace, and to try to understand the meaning of sentences at a naturalspeed with no backtracking. Absolute processability judgments (Sec. 2) weremade before relative judgments (Sec. 3) so that subjects would not knowwhat constituted the critical comparisons of the questionnaire while theywere making absolute judgments.

For the purpose of analysis, it was assumed that subjects treated therating scale as at least quasi-interval. Responses were therefore converted tonumerical values (© = 1, XX = 6), and their distribution was analyzedparametrically.

6 The example below illustrates the filling out of a sentence skeleton with lexical content,and presents a 3ga form to be adapted by -ga/-no conversion:

Haha-ga ani-ga chichi-ga kaetta toki dekaketa no-ni odoroitaMy mother-Norn my brother-Nom my father-Nom came-home time went-out fact-at surprised"My mother was surprised at the fact that my brother went out when my father came home."

The adaptation involved the third NP, chichi-ga, which became chichi-no.7 The questionnaire did not contain filler sentences for the following reason: Multiply

center-embedded sentences are not easy to process, on any account, and even a verylarge number of fillers is unlikely to distract subjects' attention from the fact that ma-terials are intrinsically difficult. The central consideration in design of the questionnairewas that processability judgments should be sensitive over the relevant range; for thisreason, anchor sentences were designed to cover a range from (somewhat) easier than,to (somewhat) more difficult than, the test cases.

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RESULTS AND DISCUSSION

259

The summary data and analyses for Sec. 2's absolute processabilityjudgments are shown in Table I. For each comparison, the 3ga versions ofsentences were rated as significantly less processable than their non-3gacounterparts. Moreover, an overall analysis (Manipulation X Comparison)showed no reliable difference in the magnitude of the 3ga cost among thecases tested, F < 1 for the interaction term. The presence of a 3ga sequenceresulted, overall, in a shift in processability of 0.86 units on the 6-pointrating scale.

Table II presents mean processability ratings for the anchor sentences.These distributed themselves on either side of a notional breakpoint fallingbetween ratings 3 and 4 on the 6-point scale. A comparison of the three

Table I. Mean Rated Processability for 3ga Sentences and Non-3ga Counterparts, forThree Kinds of Manipulation

Manipulation

-gal-no Conversion

-gal-wa Conversion Case 1

-gal-wa Conversion Case 2

-ga/-wa Conversion Case 3

ADV insertion'

Test sentence skeletons

[-ga U,,-ga U,,-ga V]]V]] V]'[-ga U,p-ga Uk-no V]]V]] V][-ga [,P-ga [,,,-ga-o V] V] V][-wa [,,-ga [,,-ga-o V] V] V][-ga[w[,,-ga,,-gaV]]V]]V][-wa Urga Urga V]]V]] V][-ga [,,-ga -ga [,,-ga V] V] V][-wa [,,-ga -ga [,,-ga V] V] V][-ga [,,-ga [,,-ga -o V] Adv V] V][-ga [,,-ga Adv [,,-ga -o V] V] V]

Meanrating

3.883.094.313.163.592.844.724.034.533.63

F-valuea

8.75'

20.07''

4.78b

8.66c

16. 19d

aDegrees of freedom (1, 30) for all comparisons.bp < .05.cp < .01.Jp < .0001.eV = verb; ADV, Adv = adverb.

Judgments of Processing Load in Japanese

Table II. Mean Rated Processability for Anchor Sentences

Sentence

AS1AS2AS3AS4

PLU"

3356

Prediction

EasyProcessableOverloadOverload!

Rating

2.473.223.844.63

• PLU - processing load unit.

PLU cases showed that the addition of two inherently cased NPs in AS2reliably increased the processing load relative to AS1, F(l, 31) = 8.45, p< .01. However, that increase in processing load amounted to less than theaddition of two full PLUs in B&G's metric; that is, AS2 (three PLUs withtwo NP -m"s) was rated as significantly less difficult than AS3 (five PLUs),F(\, 31) = 5.00, p < .05. Finally, the comparison of AS3 and AS4 showedthe processing (overload to be graded, F(l, 31) = 16.16, p < .001. It isinteresting to note that the average 3ga cost found in the test sentences (0.86rating scale units, see above) is of the same approximate order as the costassociated with one additional PLU (AS3 and AS4 differed by 0.79 ratingscale units).

An inspection of the ratings summarized in Table I reveals that, al-though the test cases were all associated with five PLUs (aside from costsof 3ga), their converted counterparts (for which ga cost is not an issue) werenot uniformly rated as unprocessable. For the -gal-no case, and for -gal-waconversion Cases 1 and 2, sequences without 3ga were given ratings ap-proximately equal to or better than the "processable" AS2. The ADVinsertion case, rated 3.63, falls intermediate between AS2 and AS3, and aprocessing load associated with the presence of an adverb may be implicatedhere. Finally, for -ga/-wa Conversion Case 3, conversion merely reducedthe length of the NP sequence marked with -ga from four to three NPs.Although this reduction was substantial in its impact, a ga cost nonethelessremained; ga cost is graded, apparently.

The weight of the evidence seems to suggest that B&G's critical limit,set at four PLUs, is pitched too low and should be revised upward. Note,however, that among the anchor sentences, AS3 with five PLUs but no 3gacost was judged to be unprocessable, and certainly the cases in Table I varyamong themselves. Apparently, not all five PLU sentences are the same;there are aspects of sentence structure or content which are still not beingtaken into account in predicting processing load. It might be that some kindsof SE, say, are more costly than others, or that there are sources of variability(beyond SE, structurally cased NPs, and 3ga cost) that impact on process-ability but are not yet recognized by any theory. This requires further re-search in which additional potential facts are varied systematically.

GENERAL DISCUSSION

The experiment has provided firm evidence in Japanese of a processingcost associated with sequences of more than two consecutive NPs markedby -ga. It has also raised the suggestion that inherently cased NPs (e.g., NP-ni) are not cost free, although this important issue is yet to be studied sys-

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tematically.8 The main experimental finding has cross-linguistic support, inRosenbaum and Kim's (1976) observation that center-embedded sentencesin Korean with more than two consecutive uses of the same nominative casemarker are more difficult to process than their counterparts in which themarker varies. And certainly guides for "good" writing style recommendagainst repeated use of a given element, e.g., Ookuma (1991) for Japaneseparticles, or Barnes (1995) for the relative pronoun in English. It may bethat this phenomenon is to be described linguistically in terms of a filterover surface form, comparable to the "double-ing" filter in English (Ross,1973) and the double infinitive filter in Italian (Longobardi, 1980).

Why the repetition of forms leads to processing difficulty remains amatter for speculation. For Japanese, the functions ascribed to -ga by thetraditional literature (e.g., Kuno, 1973, 1978) suggest some possible lines ofexplanation. If -ga is used to signal new information, too many consecutive-ga phrases may overwhelm the parser with too much information that ispresented as new. Another reported use of-ga, "exhaustive listing," is saidto pick a specific entity out of the current universe of discourse, and perhapsit cannot naturally apply repetitively since there is unlikely to be a specificcontext for each of three entities.

Another line of explanation, more directly processor oriented, suggeststhat NP-ga sequences make it difficult for the parser to form hypothesesabout structural or thematic relations. Such processing explanations supposethat parsing difficulty arises either because -ga repetition impairs discrimin-ability among NPs which await their structural assignments or because -gais of itself more structurally ambiguous than other case markers. With re-spect to the former, Rosenbaum and Kim (1976) discussed their observationof problematic case-marker repetition in Korean in terms of a phonologi-cal/morphological cue effect. Similarly, Lewis (1993) attributed processingdifficulties to syntactic interference arising from limitations on human short-term memory, and remarked on an effect of phonological discriminability.With respect to the ambiguity of -ga, research on Japanese sentence pro-cessing is not yet sufficiently advanced to spell out a proposal in any detail.What is clear is that a multiplicity of different structures can begin with thesurface sequence 3ga.9 Nagai (1995) claimed that the parser tends to mini-mally attach the second of 2ga's to the same clause as the first, anticipatinga predicate which marks its object with -ga. However, opinion differs as to

8 The status of inherently cased NPs with respect to processing load was a crucial panof B&G's argument against Stabler's (1994) case-based and Lewis's (1993) X-bar-relation based theories.

9 In this situation, any kind of device (whether a discourse based, intonational, or lexicalfactor) which minimizes potential ambiguity would be expected to attenuate the 3gacost. Uehara (1996) explored a variety of such devices.

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this structural preferences: Inoue (1991), for example, claimed that the parsertakes a second -ga as a cue to construct a new clause. Perhaps the parserlacks any clear policy, and the accumulated uncertainty is what causes over-load.

Whatever explanation is supported by further research, the findings re-ported above imply that B&G's processing overload theory needs modifi-cation. Sequences of three NT-gar's have been shown to contribute roughlyone additional PLU to the processing cost, and this cost needs to be rec-ognized by any metric. For B&G's model, this might well entail adjustingthe costs assigned to other factors (structural case, self-embedding) so thatthey combine with the 3ga cost to predict overall processing difficulty. Ad-ditionally, the weight of the evidence has suggested that the parser becomesoverloaded by sentences above five PLUs, not four PLUs. However, repos-itioning the processing load limit creates a new problem for the theory: Theuniversal character of B&G's claim is lost if the limit must be set at fourPLUs for English and at five PLUs for Japanese.

APPENDIX: ANCHOR SENTENCES

AS1 [Michiko-ga [imooto-ga Hajime-o sukida] to omotteiru]-Nom sister-Mom -Ace like that thinks

"Michiko thinks that her sister likes Hajime."

AS2 [Haha-ga Kawada-san-ni [oba-ga ani-ni Noriko-san-oMy mother-Norn -Ms.-Dat my aunt-Nora my brother-Dat -Ms.-Accshookaishita] to hanasita]introduced that spoke"My mother told Ms. Kawada that my aunt introduced Noriko to my brother."

ASS [Ichiroo-ga tomodachi-o [IP Akira-ga [IP sono seito-ga byooki-da] to-Nom friend-Ace -Nom the student-Norn sick-is that

itta] to settokusita]said that persuaded"Ichiroo persuaded his friend that Akira said that the student is sick."

AS4 [Otooto-ga Yumi-o [IP Masaru-ga [IP Kumiko-ga sensei-o sukida] to itta]brother-Nom -Acc -Nom -Nom teacher-Ace likes that saiditta] to settokusita]said that persuaded"Brother persuaded Yumi that Masaru said that Kumiko likes the teacher."

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