Journal of Japanese Linguistics 2019; 35(1): 75–136

Michael P. Mansbridge* and Katsuo Tamaoka

Ambiguity in Japanese relative clauseprocessing
https://doi.org/10.1515/jjl-2019-2005

Abstract: In Japanese, relative clauses have initial clause-type ambiguity. Because
there are no overt RC markers, the structure is realized at a locus of disambiguation, typically the head noun. While previous studies have attenuated this ambiguity, these studies have not effectively investigated the processing asymmetry
between subject/object-relatives during reading. The current study investigatedRC processing within different ambiguity contexts using eye-tracking on native
Japanese speakers. For ambiguous RCs, ORC difficulties were primarily observed
during late-processing measures after disambiguation at the head noun and RC
verb. This was possibly due to the inherent difficulty of assigning thematic roles
when the object appears outside the clause as the object-before-subject-bias
predicts or due to factors such as expectation, structural-integration and similarity
interference. Because all predict ORC difficulties in ambiguous RCs, the exact
nature of the processing remains uncertain. For unambiguous RCs, ORC difficulties were instead observed during early-processing measures at the head noun.
We attribute this to expectation-based processing because the clause no longer
requires a structural reconfiguration. Specifically, with increased cues for the RC
interpretation, expectation-based processing effects became more observable atthe head. In conclusion, clause type ambiguity is an integral factor for Japaneserelative clause processing.
Keywords: Japanese, relative clauses, ambiguity, expectation

1 Introduction
The current study aims to reveal the influence ambiguity has on Japaneserelative clause (RC) processing by investigating the classical subject/object
relative clause asymmetry. Specifically, for the majority of the world languages,
object-extracted relative clauses (ORC) have been found to be more difficult toprocess and comprehend than their subject-extracted relative clause (SRC)*Corresponding author: Michael P. Mansbridge, Nagoya University, Nagoya, Japan,
E-mail: michaelp.mansbridge@gmail.com
Katsuo Tamaoka, Nagoya University, Nagoya, Japan, E-mail: ktamaoka@lang.nagoya-u.ac.jp

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76

Michael P. Mansbridge and Katsuo Tamaoka

counterparts. While previous studies have frequently shown that ORCs are moredifficult to process in Japanese, there are many accounts that can satisfactorily
explain this difficulty. The number of theories available might even become
problematic when attempting to reach a specific or more narrowed conclusion
on RC processing. Therefore, to determine which factors are truly bottlenecks ofprocessing, more work is needed in Japanese to tease apart these processing
accounts.
In the Japanese language, RCs are often ambiguous in terms of clausestructure, which has been a contentious issue because the ambiguity allows
for a garden path effect to occur up to the head noun. While recent studies havebegun to investigate RCs in Japanese within unambiguous contexts, these studies either did not compare the asymmetry or revealed similar patterns toambiguous RCs. Therefore, the current study aims to investigate RCs in
Japanese within both ambiguous and unambiguous contexts to determine how
ambiguity influences RC processing in Japanese. In line with previous studies
arguing for hybrid models of sentence processing containing both expectationbased processing effects as well as effects of working memory, we argue that thisis also the case for Japanese RC processing. Considering that previous studies inother languages have shown that with attenuated ambiguity, expectation-based
processing becomes more salient during reading, we aim to demonstrate this inJapanese. We suspect that changes in processing behaviour will be limited to thelocus of the sentence which acts as the cue for the RC interpretation as well as
serving as the locus of integration/retrieval between the filler-gap dependencies,
i.e. the head noun.

1.1 Relative clauses
A relative clause in Japanese is a noun-modifying expression in which the headnoun is required to be a grammatical argument within the clause itself.
According to Na and Huck (1993: 197) argument condition, “A RC must containan element E that the clause predicates something of, where E is either (A) a
gap co-indexed with the clause head or (B) a nominal whose denotation isthematically subordinate to that of the head noun”. Accordingly, RCs would
differ from other similar structures in which the head does not satisfy one ormore of the above conditions. For instance, while other embedded clauses (e.g.
[-koto] ‘thing/about that’ and [-zizitu] ‘fact that’) and gapless-RCs bear a similarity to RCs, their heads have no co-reference to any grammatical position
within the clause. Thus, they should not be considered to fall under the
specific category of RC.

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Ambiguity in Japanese

77

While there are many types of relative clauses, this study will focus on only
two types, that is, subject-extracted relative clauses and object-extracted relative
clauses. When discussing RC processing, the term filler-gap parsing is often
used. The filler is the co-indexed element that fills the gap created at the trace ofa wh-movement. In the glossed English examples below, it can be seen that thehead noun is co-indexed with the relative pronoun which originated from adeeper syntactic position within the RC where grammatical assignment and caseis received. Afterwards, the relative pronoun undergoes wh-movement to the leftedge of the clause where it can assign wh-features to the clause. Because there
are no overt RC markers in Japanese, this interpretation of RCs might be problematic. Admittedly, the underlying structure for RCs in Japanese is debated. Some
researchers (Bugaeva and Whitman 2016; Kaplan and Whitman 1995) consider
there to be a gap within the RC which might involve covert movement of awh-operator, similar to reduced-RCs in English (Browning 1987). In contrast,
others (e.g. Comrie 2008; Davis 2006; Matsumoto 1997) disagree and instead
argue that there is a null/empty pronominal element which is co-indexed withthe head. While Watanabe (2003) claimed that covert operator movement exists
for head-internal RC arguments, he was hesitant making the claim for typicalhead-external RCs due to the opposition against movement. However, because
Bugaeva and Whitman (2016) demonstrate that RCs are distinct from other nounmodifying expressions due to island violations, we henceforth assume a gappedinterpretation. See examples below.
(1)1

a. Subject-extracted relative clause (SRC)
市長を非難したレポーターは医師を面接した。
[GAPi Sityô-o hinansita] repôtâi-wa ishi-o mensetusita.
[GAPi mayor-ACC criticized] reporteri-TOP doctor-ACC interviewed‘The reporteri [whoi GAPi criticized the mayor] interviewed the doctor.’
2b. Object-extracted relative clause (ORC)
市長が非難したレポーターは医師を面接した。
[Sityô-ga GAPi hinansita] repôtâi-wa ishi-o mensetusita.
[mayor-NOM GAPi criticized] reporteri-TOP doctor-ACC interviewed‘The reporteri [whoi the mayor criticized GAPi] interviewed the doctor.’

1 Abbreviations used are as follows: ACC (Accusative), TOP (Topicalizer).
2 Abbreviations used are as follows: NOM (Nominative).

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78Michael P. Mansbridge and Katsuo Tamaoka

1.2 Ambiguity in Japanese relative clauses
Temporary ambiguity can lead the mental parser to a classic garden path effect,
i.e. an initial misinterpretation of word meaning or sentence structure which
requires a reanalysis at a point of disambiguation within the sentence. However,garden path effects can be attenuated using a variety of methods such as
discourse priming, prosody, punctuation or syntactic cues. Similar to
Mandarin Chinese and Korean, Japanese is an East Asian language which has
prenominal RCs, i.e. head-final, and exhibit temporary clause-type ambiguity. In
Japanese, RCs typically lack overt marking, and the language also permits
pronominal dropping and syntactic scrambling. These features permit
Japanese RCs to be ambiguous. Importantly, out-of-the-blue RC-initial expressions lack RC-specific discourse and syntactic markers. Thus, when encountered, the mental parser is likely to incorrectly assign a matrix-clauseinterpretation to the RC structure until a viable cue signals otherwise. This cue
can be considered as the locus of disambiguation. In Japanese, this point isregularly the head noun of the RC. Yet, even if an initial cue is given to disregard
a matrix clause interpretation, other embedded clause interpretations are available. For example, because-adjuncts, fact-expressions and gapless-RCs can lookidentical to an RC up to the embedded verb. Therefore, an RC interpretation isdifficult to form until the head noun is parsed. As illustrated in the fragments(2a) and (2b) below, the initial word orders between these fragments are identical to (1a) and (1b) on the surface up to the head of the structure.
(2)3

a. Subject-drop fact clause
市長を非難した事実[pro Sityô-o hinansita] zizitu[pro mayor-ACC criticized] fact
‘The fact [(that) someone criticized the mayor]’b. Object-drop fact clause
市長が非難した事実[Sityô-ga pro hinansita] zizitu[mayor-NOM pro criticized] fact
‘The fact [(that) the mayor criticized someone]’

3 Abbreviations used are as follows: pro (Pronominal).

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Ambiguity in Japanese79

1.3 Attenuating ambiguity
Past Japanese studies have attenuated ambiguity using discourse-priming(Miyamoto 2016; Miyamoto and Tsujino 2016), punctuation (Niikuni and Muramoto2014), prosodic effects (Hirose 2003), clause-type plausibility (Nakamura and Arai
2015), successive case marking (Miyamoto 2002), pre-RC cues (Kahraman et al. 2014)
and post-RC cues (Arai and Kahraman 2016; Arai 2017). The bulk of these studies
observed that the processing burden for RC processing at the head noun can beattenuated when the RC becomes unambiguous. For example, there is an increased
probability of an embedded clause when the sentence contains successive casemarkings (Miyamoto 2002). Both the sentences (3a) and (4b) below are ambiguous.
The verb ‘interrogated’ appears to be a matrix predicate until the head noun ‘policeman’ is encountered. On the other hand, because ‘Tanaka’ and ‘reporter’ in (3b) and(4a) have the same case marking, it becomes likely that the second noun is contained
within an embedded clause. This creates a clause boundary between the two nouns(Miyamoto 2002; Yamashita 1995). Thus, the head noun is easier to parse because it
lacks structural reanalysis and is anticipated. In contrast, (3a) and (4b) should have agarden path effect at the head causing a reading slowdown.
(3)

a. in situ object-modified SRC
田中がレポーターを尋問したお巡りさんを見た。
Tanaka-ga [repôtâ-o zinmonsita] omawarisan-o mita.
Tanaka-NOM [reporter-ACC interrogate] policeman-ACC saw.
‘Tanaka saw the policeman who interrogated the reporter.’b. in situ object-modified ORC
田中がレポーターが尋問したお巡りさんを見た。
Tanaka-ga [repôtâ-ga zinmonsita] omawarisan-o mita.
Tanaka-NOM [reporter-NOM interrogate] policeman-ACC saw.
‘Tanaka saw the policeman who the reporter interrogated.’(4)

a. scrambled subject-modified SRC
田中をレポーターを尋問したお巡りさんが見た。
Tanaka-o [repôtâ-o zinmonsita] omawarisan-ga mita.
Tanaka-ACC [reporter-ACC interrogate] policeman-NOM saw.
‘The policeman who interrogated the reporter saw Tanaka.’b. scrambled subject-modified ORC
田中をレポーターが尋問したお巡りさんが見た。
Tanaka-o [repôtâ-ga zinmonsita] omawarisan-ga mita.
Tanaka-ACC [reporter-NOM interrogate] policeman-NOM saw.
‘The policeman who the reporter interrogated saw Tanaka.’

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80Michael P. Mansbridge and Katsuo Tamaoka

This design, however, might not be suitable to compare SRC and ORC
processing because it does not allow for equal comparisons. To specify, in two
conditions successive case creates a clause boundary while the other two retain
a garden path effect. Furthermore, these garden paths are not equal as (3a)appears to be a canonical matrix clause while (4b) appears to be a matrix clause
involving simple scrambling. Additionally, comparing (3b) and (4a) is problematic because the successive case in (4a) appears to violate the double-o constraint (Harada 1973), i.e. two accusative marked nouns cannot appear within
the same verb phrase, and (4a) also involves scrambling. Therefore, we argue
that other contexts are needed which lack these confounds.
Another method of attenuating ambiguity is using pre-RC cues to enhance
the RC interpretation, implemented by Kahraman et al. (2014). In their study on
Japanese processing, they inserted numerical classifiers in the pre-RC position
which either matched or mismatched with the RC noun. See fragments of their
examples below.
(5)4

a. Match-SRC
一人の快活なおじさんを真似した黄色い鸚鵡
Hitori-no kaikatuna ozisan-o manesita kîroi ômu
1 person-GEN cheerful uncle-ACC imitated yellow parrot‘The yellow parrot that imitated one cheerful uncle’
b. Match-ORC
一人の快活なおじさんが真似した黄色い鸚鵡
Hitori-no kaikatuna ozisan-ga manesita kîroi ômu
1 person-GEN cheerful uncle-NOM imitated yellow parrot‘The yellow parrot that one cheerful uncle imitated’c. Mismatch-SRC
一羽の快活なおじさんを真似した黄色い鸚鵡
Itiwa-no kaikatuna ozisan-o manesita kîroi ômu
1 bird-GEN cheerful uncle-ACC imitated yellow parrot‘One yellow parrot that imitated the cheerful uncle’d. Mismatch-ORC
一羽の快活なおじさんが真似した黄色い鸚鵡
Itiwa-no kaikatuna ozisan-ga manesita kîroi ômu
1 bird-GEN cheerful uncle-NOM imitated yellow parrot‘One yellow parrot that the cheerful uncle imitated’

4 Abbreviations used are as follows: GEN (Genitive).

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Ambiguity in Japanese

81

Their results revealed that when the classifier matched with the RC noun,
ORC difficulty was observed at spillover regions to the head noun. In contrast, when the classifier mismatched, ORC difficulties were not observed.
They thus concluded that with an increased expectation for an RC structure,processing difficulties can be attenuated, and that the numerical classifier
mismatch cue is effective at eliminating ambiguity. However, there is one
issue with this paradigm which might have allowed for ORCs to become justas easy/difficult to parse than SRCs. Specifically, the animacy values for the
RC noun and head noun could be problematic for their account. It is wellknown that animacy contrast is a major factor for RC processing. For example, it is often found that SRCs are preferred to have an animate head andinanimate RC noun with ORCs being the opposite (e.g. Mak et al. 2002;
Traxler et al. 2005; Wu et al. 2011). Considering this, Japanese is likely to be
similar. Accordingly, in the sense that many classifiers are for inanimate
objects or for animals which are lower on the animacy hierarchy scale thanhumans (c.f., Aissen 1999; Ransom 1977) there should be higher expectations
for ORCs when said classifiers are provided, thus attenuating some difficulty.
This by no means diminishes the value of the findings by Kahraman et al.
(2014) but instead implies that their findings might relate more to the particular expectations attributed to the distributions of animacy contrast rather
than the frequencies of RCs as a whole. Bearing in mind that the distributionsof RCs are more equal when both nouns are animate, it might be better to test
RCs in this more neutral environment. Thus, pre-RC numerical classifiers
might not be the best method in this case.
While post-RC cues, occurring after the RC and before the head, can also
attenuate ambiguity, clause-type ambiguity is not attenuated until after processing the RC structure. Instead of the head noun being the locus of disambiguation, the garden path effect would only occur up to the cue. See examples (6a-c)
below from Arai and Kahraman (2016) and Arai (2017).
(6)

a. SRC + Adjective
大学院生を非難した意地悪な研究者
Daigakuinse-o hinansita iziwaruna kenkyusya
graduate.student-ACC criticized mean researcher‘The mean researcher who the graduate student criticized’b. SRC + Genitive
大学院生を非難した風力発電の研究者
Daigakuinse-o hinansita hȗryokuhatsuden-no kenkyusya
graduate.student-ACC criticized wind.energy-GEN researcher‘The wind-energy researcher who the graduate student criticized’

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82Michael P. Mansbridge and Katsuo Tamaokac. SRC + Demonstrative
大学院生を非難したその研究者
Daigakuinse-o hinansita sono kenkyusya
graduate.student-ACC criticized that researcher‘That researcher who the graduate student criticized’
Such cues can be demonstratives, adjectives, or genitive phrases. Recently, Arai(2017) investigated Japanese RC processing using these cues and found thatasymmetry between RCs can be explained by the structural frequencies of thelanguage (i.e. expectation-based processing). Yet, this design also permits agarden path effect during the initial parsing of the RC. Therefore, to view theprocessing of RCs without a garden path effect, pre-RC cues are more appropriate in this regard. Consequently, for the current study, we decided to use preRC demonstrative cues, discussed in Section 2.3.6.

1.4 Processing theories
In the following subsections, several processing theories are described and theirrelation to Japanese RC processing is spelled out. The following processing
accounts are by no means an exhaustive list for RC processing. We have limited
the discussion to memory-mechanisms and expectation-based processing
because they are prominent accounts of RC processing. The object-beforesubject-bias theory is also included as a recent counter-hypothesis to both
expectation and memory.

1.4.1 Integration-based resources
For filler-gap dependencies (Clifton and Frazier 1989; Fodor 1989), the headnoun is required to be integrated with the gap to assume its grammatical role
within the RC. Otherwise, the RC would not be properly understood. For integration processes (Gibson 2000; Lewis and Vasishth 2005; O’Grady 1997), theprocess is generally understood as a function of working memory and that theactivation level of a referent in working memory decays. Thus, the processing
burden associated with integration is contingent on the level of decay, which,however, is measured differently between theories.
According to Gibson’s (2000) dependency locality theory (DLT), the metric ofintegration is often described as the linear metric because the processing work
during integration increases as the number of intervening referents between the

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Ambiguity in Japanese83

filler and gap increase on the surface structure, not the syntactic. In Japanese,the distance between the head noun and gap is greater for SRCs in comparison
to ORCs, indicating that the integration process should be more demanding in
SRCs. In contrast, the predictions made in English call for greater ORC difficulty
because the gap is more distant in the object position. The differences withEnglish are not limited to Japanese as other prenominal languages such as
Korean and Mandarin display this pattern as well.
In a similar vein to the DLT, Lewis and Vasishth’s (2005) activation-basedmodel, based within the scope of the adaptive control of thought–rational (ACT-R)
model (Anderson 1996), proposes that the decay of the initial activation increases
as a function of time, i.e. the temporal metric. This metric of integration also
predicts greater SRC difficulty in Japanese which again contrasts with English.
Because this metric makes the same prediction as DLT (i.e. greater SRC difficultyin Japanese), these two accounts will henceforth be collapsed into a single
account for the purpose of this study.
Lastly, the structural-phrase hierarchy model (O’Grady 1997) instead proposes that the decay in memory is attributed to the number of intervening
phrases in syntactic hierarchy, i.e. the structural metric. This model directly
contrasts with the above because intervening material on the surface, which
does not intervene between two co-indexed dependencies in structure, does not
impact the level of decay. In Japanese, because there are more intervening
syntactic phrases in hierarchy between the filler and gap for ORCs, there isgreater difficulty for ORC processing than SRC processing. This is also true inEnglish and is a near language universal. Refer to Figure 1 below for an
illustration of each metric in English and Japanese.
As mentioned, the syntactic structure for Japanese RCs is debated.
Importantly, the above predictions for the linear/temporal metrics are contingent
upon the syntax. To clarify, for syntactic interpretations involving covert whmovement, there is an additional issue as to where the operator moves. If it
moves to the left [Spec, CP], i.e. the left of the clause, ORCs would be predicted
to be more difficult because the distance between the gap and operator would be
more local for SRCs. In contrast, if it moves to the right of the clause, i.e. between
the RC and the head, then the above predictions would not change. This issue wasalso addressed by Ueno and Garnsey (2008) who ultimately measured the direct
distance between the filler and gap. While we claim that RCs are a result of
movement in Japanese, we also do not take a hard stance on the exact nature ofthis movement and thus will retain the above predictions. In Figure 1 below, we
include operators at left [Spec, CP] of the Japanese RCs for reference.
In summary, for Japanese there are contrastive predictions based upon themetric used to define the distance between the filler and gap. It is currently

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84Michael P. Mansbridge and Katsuo Tamaoka

English SRC

English ORC

The reporter i [who t i criticized the mayor]

The reporter i [who the mayor criticized t i]

NP

NP

The reporteri CP

The reporteri CP

who

who

IP

NP
ti

IP

NP

VP

VP

the mayor
criticized NP

criticizedNPti

the mayor

Japanese SRC

Japanese ORC[t i mayor-ACC criticized] reporter i[mayor-NOM t i criticized] reporter iNP

NP

CP reporteri

CP reporteri

OPi

IP

OPi
NP
ti

VP
NP

NP

criticizedmayor-ACC

IP
VP

mayorNOM NP

criticizedtiFigure 1: Integration metric predictions for English and Japanese RCs.

believed that when defining distance by either the linear or temporal metric
SRCs should engender difficulty, while ORCs would induce difficulty if integration is defined by structural distance.
The linear/temporal metric distance is indicated by the horizontal arrow,and the longer the arrow, the greater the decay in memory. The structural-phrase

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Ambiguity in Japanese85

metric distance is indicated by the circles around the phrases, and the morephrases circled intervening between the filler and the gap, the greater the decay.

1.4.2 Expectation-based processing
Expectation-based Processing (Hale 2001; Levy 2008) models are probabilistic
models of processing which assume processing is incremental (e.g. Gerry TM
and Kamide 1999) and is constantly drawing from prior language exposure to
make predictions for the upcoming structure. As described by Levy’s (2008)
surprisal theory, at each individual word, ranked-parallel expectations arebeing formed and revised based upon the structural frequencies of the possible
structures which can match with the ongoing input. Processing work describedhere generally reflects the difficulty in revising the ongoing expectation when an
unexpected or less frequent structure is encountered. This can be understood as
a less frequent structure being more difficult to process than a more frequent
structure at a point where two structures diverge.
For languages such as English (Staub 2010), Russian (Price and Witzel 2017),
Korean (Kwon et al. 2010; Mansbridge et al. 2017a) and Mandarin (Jäger et al.
2015; Mansbridge et al. 2017b), expectation-based processing has been well
supported in terms of RC frequencies. For the structural frequencies ofJapanese RCs, it has been shown that ORCs occur less often in corpora thantheir SRC counterparts. Both Collier-Sanuki (1993) and Yun et al. (2015) foundthat SRCs occur more frequently than ORCs. While Collier-Sanuki (1993) usedtranslated novel corpora to reveal RC frequencies, Yun et al. (2015) used the
Kyoto Corpus 4.0 (Kurohashi and Nagao 2003). From their investigation it was
revealed that SRCs (537 token counts) are overwhelmingly more frequent thantheir ORC counterparts (116 token counts) in Japanese, which is significant by achi-square goodness of fit test, χ2 (1, N = 653) = 271.43, p < 0.001. Thus, despite
arguments that ORCs occur just as often than SRCs as revealed by child acquisition studies (Ozeki and Shirai 2007) and sentence completion tasks producing
varied results (c.f., Kahraman et al. 2014; Miyamoto and Tsujino 2016; Nakamura
and Miyamoto 2012; Ueno and Garnsey 2008), corpora evidence shows that SRCs
occur statistically more frequent than ORCs; thus, ORCs should be more difficult
to process.
There is a simple explanation as to why sentence completion tasks revealed
mixed findings. Simply, the ORC fragments are more constrained to RC interpretations due to the rarity of object pro-drop while SRC fragments allow for
greater variation. This reasoning, however, does not necessarily imply that ORCs
invoke a higher expectation during reading than SRCs because attestation

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86Michael P. Mansbridge and Katsuo Tamaoka

accounts for both SRCs and complement clauses with a pro-drop subject are
higher than ORCs (Yun et al. 2015). Accordingly, it is possible that despite theinitial expectation made upon an SRC fragment, the amount of work required torevise the expectation during reading should be less than an ORC fragment due
to the bias for a subject gap or pro within a ranked-parallel parser. In otherwords, despite the structural probabilities of an ORC fragment favouring an RC
structure for offline production purposes, the processing work required to reachsaid structure during reading is greater. Considering the initial-clause typeambiguity, however, these effects should not be observed until the correct RCinterpretation is realized at the head noun. This implies that a garden path effectexists up to this locus of disambiguation.
For unambiguous RCs, on the other hand, the first cue in the sentence that
could potentially indicate the RC type (e.g. ORC or SRC) would be the casemarking on the RC noun. If only an accusative noun is given, then the structure
should be interpreted as being an SRC. In contrast, if a noun marked withnominative case is provided, then an ORC should be understood. Thus, ORC
difficulty should be observed prior to the head noun if the RC structure isunderstood properly.
Another frequency-based account is the entropy reduction hypothesis (Hale2006; Yun et al. 2015). While Hale claims that the underlying calculations offrequency are similar to that of surprisal (Levy 2008), Hale interprets processing
difficulty to be the result of reductions in the structural entropy between words.
According to Hale, there is a degree of uncertainty left in the structure at each
word, and when this level of uncertainty is lowered at the subsequent word,
processing work has occurred. In Yun et al. (2015), the entropy levels for the
structure were calculated at each word of the RC, and according to their findings, an ORC should be more difficult to process because its structure has
greater drops in entropy compared to an SRC structure.
Starting with the RC noun without morphology, both structures are reported
by Yun et al. (2015) to have the same level of entropy. The structural probabilities at this point in the sentence overwhelmingly favour a matrix clause interpretation. This mono-clausal structure is likely to be an intransitive clause,transitive clause with subject pro drop and a transitive clause with two overt
arguments respectively. Unsurprisingly, given just a noun, no processing differences are predicted between RC conditions.
According to Yun et al. (2015), differences between conditions begin at themorpheme affixed to the RC nouns. The differences in case morphology between
ORCs (i.e. nominative case) and SRCs (i.e. accusative case) should reveal agreater reduction in entropy for ORCs because the nominative case would likely
constrain the noun’s interpretation as being a subject in a matrix clause with

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Ambiguity in Japanese87either an intransitive or transitive predicate respectively. In contrast, the SRC atthis point is highly likely to be a matrix clause with a subject pro-drop followedby an RC interpretation, thus having higher reported entropy. Consequently, as
early as the reading of the case morpheme affixed to the RC noun, ORCs are
predicted to engender processing difficulty.
Moving on to the verb, while the structural probabilities do not change for
SRCs, ORCs probabilities are reported to change to a transitive matrix clausewith a missing object and an RC respectively (Yun et al. 2015). In comparison to
SRCs, Yun et al. (2015) report that the overall likelihood for pro in the SRC
fragment is greater than the probability of pro in the ORC fragment.
Accordingly, despite object pro being rare and SRCs being more frequent,
there is greater certainty for pro in SRC fragments while ORC fragments are
more uncertain between pro and gap. Because neither structure has a reduction
in entropy, neither structure is predicted to be more difficult than the other.
At the head noun, Yun et al. (2015) predict that ORCs should engender
processing difficulty due to another reduction in entropy while SRC entropy isreported to increase when eliminating the pro interpretations. It is important tospecify that this model predicts ORC difficulty at the RC noun and head noun for
ambiguous Japanese RCs. For unambiguous RCs, Yun et al. (2015) speculate thatno difficulty would be invoked if the structure is understood. Relating back to
the particular expectations invoked by the ongoing structure, we, however,argue that it is important to consider both the overall statistical distribution of
structures in corpora and the structural probabilities for the ongoing structure of
an ambiguous RC fragment.

1.4.3 Similarity-based interferences
Similarity-interference is another working memory account for processing difficulty. Generally speaking, when two referents are stored into working memory
with similar features, there is greater difficulty in selecting a specific referent
from memory due to the interference from the other. However, the details ofsimilarity-interference are not agreed upon. While some see it as difficulty instorage, encoding, maintenance and retrieval (e.g. Gordon et al. 2001), others
consider difficulty to occur primarily during retrieval (e.g. Lewis and Vasishth2005). For an overview on these points, refer to Lewis et al. (2006). To put it
succinctly, while reading sentences, the parser stores and maintains noun
dependents with their assigned syntactic and semantic features in working
memory for later reactivation and integration with their respective verbs or
anaphora. Accordingly, if two or more similar nouns are stored in memory,

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88Michael P. Mansbridge and Katsuo Tamaoka

they might interfere with each other during the retrieval of one of them. This
would also be modulated by how similar these nouns are. As they become moresimilar in gender, number, noun type, semantic or grammatical role, the interference will also become greater.
For Japanese RCs, ORCs should incur a greater processing cost due tosimilarity-interference in comparison to SRCs because both the ORC noun andhead noun share overlapping features in grammatical role (e.g. subject role).
Specifically, the RC noun would proactively interfere with the head noun for
ORCs during the retrieval of the matrix subject at the matrix verb. Also considering Gordon’s account for similarity-interference, late-stage difficulty might also
be observed at the head noun or even within the RC if the head noun retroactively interferes with the RC noun.

1.4.4 The object-before-subject-bias
Nakamura and Miyamoto (2013) claim that ORC difficulty can be better
explained by other processing accounts rather than expectation and working
memory. Within the framework of their object-before-subject-bias model, ORC
difficulty in Japanese can be explained by difficulties in thematic assignment.
Drawing upon the verb-object bonding principle for transitive arguments (Tomlin1986), the claim that the thematic role of the direct object is assigned by thetransitive verb and the subject’s role by the direct object, Nakamura andMiyamoto (2013) argue that when each argument is stated (i.e. overt; see
Nakamura and Miyamoto 2013 for understated, dropped arguments inJapanese) there is inherently greater difficulty for ORC constructions. See
below for an example of how the object regulates the assignment of the thetarole for the subject.
(7)

English example
Prefix string: The man caught…
Theta Role Option 1: a ball [‘the man’ becomes <agent> ]Theta Role Option 2: a cold [‘the man’ becomes <experiencer> ]They claim that not only is there greater difficulty for ORCs because the object
argument is juxtaposed outside the clause as a head in comparison to when it iswithin the clause, there is also greater difficulty with ORCs because of howthematic roles are first assigned for the object head and then back to the RC
subject. In comparison with SRCs, the assignment of the subject head’s thetarole requires only one step at the head noun. This difficulty in assignment, they

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Ambiguity in Japanese

89

claim, would manifest itself at the head noun and the RC verb as well. See below
for examples of the ordering of thematic roles.
(8)

Ordering of thematic arguments: Japanese examples
SRC: 市長を非難したレポーター
Sityô-o hinansita repôtâmayor-ACC criticized reporter-NOM[Theta role assignment: (1) the object ‘mayor and then (2) the subject‘reporter’. In other words, the RC theta role for ‘reporter’ is immediately assigned.]
ORC: 市長が非難したレポーター
Sityô-ga hinansita repôtâmayor-NOM criticized reporter-NOM[Theta role assignment: (1) the object ‘reporter’ and then (2) the
subject ‘mayor. The RC theta role for ‘senator’ is assigned after
reading ‘reporter’.]However, as Nakamura and Miyamoto (2013: 324) note, the assignment of thethematic role for the subject can appear prior to the integration of an object due
to anticipatory resources. This is a probable scenario for unambiguous Japaneseclauses, which would allow the assignment of thematic roles to occur earlier outof greater anticipation for a head noun. As such, we believe that this would
remove some processing difficulty related to thematic role assignment at thehead noun and RC verb. However, if the subject/object asymmetry persists at thehead, then other processing accounts might be indicative of the difference when
the clause is unambiguous, especially because the clause would no longer
require a major structural reanalysis. Considering evidence for expectationbased resources in other prenominal RC languages such Mandarin (Jäger et al.
2015) and Korean (Kwon et al. 2010) when the RC is unambiguous, we predict tofind evidence of expectation-based resources in Japanese.

1.5 Current issues
Most of the current literature surrounding East Asian languages with prenominal
RCs is now investigating the classical processing asymmetry between SRCs and
ORCs using unambiguous RCs. This is because RC ambiguity is viewed as anundesired confound. However, many of the above Japanese studies, which usedunambiguous RCs, either did not account for RC asymmetry or did not offer ideal
circumstances for investigating the differences in processing. For past studies

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90Michael P. Mansbridge and Katsuo Tamaoka

using ambiguous RCs in Japanese (Ishizuka 2005; Kahraman et al. 2011;
Kahraman and Sakai 2015; Miyamoto and Nakamura 2003; Ueno and Garnsey2008), it was clearly observed that ORCs, as in many other languages, were moredifficult to process and comprehend compared to SRCs. Some of these studies
explained ORC processing difficulty in Japanese from the perspectives of theaccessibility hierarchy (Keenan and Comrie 1977), which posits that the subject
position is in a more accessible position within the RC compared to the object
position, and the syntactic-phrase hierarchy integration metric (O’Grady 1997).
However, ambiguous RCs are not an ideal context to properly compare these
conditions because both require structural reanalysis at the head noun.
One case study investigating the processing of ambiguous RCs in Japanese is
Ueno and Garnsey (2008). In their study, they investigated processing using
both self-paced reading and event related potentials (ERP) methods and foundboth behavioural and electrophysiological evidence for ORC difficulties at thehead noun. Yet, mixed evidence for ORC difficulties were seen at the RC verb.
Particularly, while ERPs revealed ORC difficulty, response times were seen to belonger for SRCs. The overall importance of this study was that the ERP results
were found to be similar to that of studies detailing filler-gap dependencies inEnglish. Specifically, the greater frontal-bilateral anterior negativity at the RCverb (at the 300 to 600 ms timecourse) and the greater centro-posterior positivity
at the head noun (starting at the 500 ms timecourse) were similar to the lateralanterior negativity (i.e. the LAN effect) and positivity around the 600 ms timecourse (i.e. the P600 effect) for ORCs in English (Kaan et al. 2000; Kluender andKutas 1993). As such, Ueno and Garnsey (2008) concluded that the ORC difficulties found in their study reflected difficulties of integration. Importantly, theyargued that these difficulties were manifested by a long-distance dependency
being integrated with the head noun as defined by the structural-integration
metric (O’Grady 1997).
They did, however, note two counter-explanations of their findings. First,
the bilateral-anterior negativity for ORCs at the RC verb could instead reflect theparser’s sensitivities to subject/object-pro drop (Kaan and Swaab 2003). Second,
the P600 effect at the head can reflect either the process of syntactic reanalysis
or the effects of syntactic expectation rather than integration (Osterhout andHolcomb 1992; Osterhout et al. 1994). While they ultimately dismissed thesepoints, they are nevertheless important to keep in mind. This is because there
are multiple processing factors that can collectively engender ORC difficulties
within ambiguous Japanese RC and overburden the parser for both RC types. As
such, it is imperative to manipulate sentential contexts to observe the subtle
changes in processing behaviour. In other words, only investigating processing
in ambiguous or unambiguous contexts is problematic.

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Ambiguity in Japanese91

Another issue relates to the nature of the Japanese RC structure and theprinciples of working memory during sentence processing. Nakamura andMiyamoto (2012) and Miyamoto (2016), drawing upon the aspect of closure(Frazier and Fodor 1978) and the fact that Japanese is head-final and an earlyclosure language, argue that at the embedded RC verb, the clause would close,
and the contents would be purged from working memory prior to integration of
the head noun. Therefore, the processing of ambiguous RCs in Japanese isunlikely to use memory-based resources related to the integration/retrieval offiller-gap dependencies. Additionally, these studies also contend that expectation-based processing (Hale 2001; Levy 2008) might not be a principal factor forJapanese RC processing as well (see Kahraman et al. 2014; Nakamura andMiyamoto 2012; Miyamoto and Tsujino 2016; Ueno and Garnsey 2008 for conflicting evidence for expectations in Japanese). Yet, as Levy (2008: 1,116) puts it,
observations of expectation are likely to be masked by other operations such as
integration. In Japanese, structural reanalysis at the head might be preventing
expectation effects from being seen clearly.
In summary, for RC processing in Japanese, it is well known that ORCs are
more difficult; yet, there are many competing accounts which support thegeneral finding that ORCs are more difficult to process than SRCs. What ismore, these investigations, while addressing ambiguity as a potential factor,
have not fully addressed ambiguity as a factor because comparisons were chiefly
made within ambiguous or unambiguous RCs. These investigations were carriedout without a proper comparison of effects between the two contexts which
eliminated confounds such as the garden path effect. Consequently, an investigation is needed to compare the processing of both ambiguous and unambiguous RCs which are attenuated by a method which can be used equally for both
RC types.

1.6 Current study
The current study investigates RC processing in Japanese via two eye-tracking
experiments. Each experiment differs with respect to the level of the initialclause type ambiguity. The experiments demonstrate how processing patternschange under different ambiguity contexts at the head noun. Specifically, thisstudy explores the detailed patterns of reading behaviour within a normal
reading design by using eye-tracking. Experiment 1 compares the processing ofstrictly ambiguous RCs in Japanese, while Experiment 2 compares both ambiguous and unambiguous RCs by inserting a potential syntactic cue to help
attenuate clause-type ambiguity. We predict that ambiguous and unambiguous

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92Michael P. Mansbridge and Katsuo Tamaoka

contexts each have distinct patterns of processing. Particularly, we predict thatthe object-before-subject-bias will account for the processing asymmetry when
the clause is ambiguous, and once the clause-type ambiguity has been attended
to, expectation-based resources will explain the processing difference.

2 Experiment 1
The main purpose of Experiment 1 was to replicate the results from previous
studies which used ambiguous RCs in Japanese. Specifically, we wished toreplicate the results of Ueno and Garnsey (2008) using eye-tracking and investigate which accounts would explain RC difficulties. As previously mentioned,
their results revealed that within ambiguous RCs in Japanese, ORCs were foundto be more difficult to process at the head noun. Accordingly, when using eyetracking we predicted that ambiguous Japanese ORCs would be more difficult toprocess at the head noun compared to SRCs.

2.1 Methods
2.1.1 Participants
Thirty-three (Female = 16) native Japanese speakers were recruited from a
University in Japan. These participants were undergraduate, graduate or research
students at the time of the study. The mean age of the participants was 22 years
and 3 months; ranging from 18 years and 8 months to 46 years and 2 months.

2.1.2 Materials
All 40 relative clause (SRC vs. ORC) experimental items were taken from Ueno
and Garnsey (2008). These items were put into counterbalanced lists to ensurethat participants would only see one RC variant for each item. An additional ten
practice and 50 distractor items were included in each list. SRC and ORC
conditions only varied by the case marking attached to the RC noun (i.e.
accusative or nominative case). The head noun was an oblique adjunct marked
with a dative and topic marker to reduce the chance of perspective shift effects(MacWhinney 1977, 1982), i.e. the difficulty of maintaining and shifting perspectives within a sentence, and similarity-based interference effects.

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Ambiguity in Japanese

(9)5

93

a. Subject-extracted relative clause (SRC)
せこい議員を非難した記者には長年の相棒がいた 。
[GAPi Sekoi giin-o hinansita] kisyai-ni-wa naganenno aibô-ga ita.
[GAP i stingy senator-ACC criticized] reporter i-DAT-TOP long.term
colleague-NOM existed‘The reporter who criticized the stingy senator had a long-termcolleague.’b. Object-extracted relative clause (ORC)
せこい議員が非難した記者には長年の相棒がいた 。
[Sekoi giin-ga GAPi hinansita] kisyai-ni-wa naganenno aibô-ga ita.
[stingy senator-NOM GAPi criticized] reporteri-DAT-TOP long.term
colleague-NOM existed‘The reporter who the stingy senator criticized had a long-termcolleague.’

2.1.3 Apparatus and procedure
Stimulus sentences were displayed horizontally on the centre left of a computer
monitor at a distance of 70 cm from the head and chin rest mount. All characters
were displayed in Japanese MS P Gothic 22pt. Eye-movements were recorded
using an EyeLink 1000 Core System (SR Research Ltd., Ontario, Canada). The
sampling rate was 1000 Hz An attached gamepad was used for buttonresponses.
Participants were instructed in Japanese that they would be reading
Japanese sentences one at a time on the computer monitor. Prior to eachstimulus, a drift-checking mask was presented at the centre left of the screen,
the point at which the sentence would begin. Once the participant accurately
fixated on the mask, the proctor would remove the mask and display thesentence. Participants were given a maximum time of 12 seconds to read thesentence and were instructed to press a button on an interfaced gamepad when
they had finished reading and comprehending the sentence. When the participants pressed the button, the sentence was replaced with a comprehension
probe (e.g. Did the reporter hit the senator?). Participants were given a maximumof eight seconds to answer the question using “TRUE” or “FALSE” marked
buttons on the gamepad. Reading times were collected from the onset of astimulus item to the button response. Prior to each session and periodically

5 Abbreviations used are as follows: DAT (Dative).

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94Michael P. Mansbridge and Katsuo Tamaoka

throughout the session, participants’ eyes were calibrated using a 9-point calibration and validation technique.

2.1.4 Eye-tracking measures
Reading time measures were collected for each word of the sentence. The earliest processing measure reported here is first-fixation duration which refers to
only the first fixation made in an interest region. Next is first-pass time which iscomposed of all fixations made within an interest region from when it is firstentered until it is exited in either direction. This measure can be a collection of
one or more fixation points; thus, it is equal to or greater than first-fixation
duration. Next is go-past time which is the total reading of an interest region
before it is exited to the right for the first time. Go-past time also includes any
regressive readings out of the region to the left before going right. Therefore,go-past time is greater than or equal to first-pass time. For eye-tracking studies,go-past has been observed to be an indication of early or late stages of processing, depending on the context in which it is found. For RC processing inparticular, the phenomenon of integration is often observed during go-pasttime at the given locus for both post-nominal and prenominal RC languages.
The late reading time measures reported in this study are re-reading time
which is the sum of all fixations after first-pass RT for an interest region (dwell
time in the region minus first-pass RT) and dwell time which is the sum of all
fixations in an interest region. Dwell time, however, is also representative ofearly effects. Additionally, regression-out (i.e. first-pass regression-out) andregression-in proportion measures are reported. In this study, we report on thesentence as a whole and all regions except the initial adjective: RC noun, RC
verb, head noun, adjective, matrix object and matrix verb. For more on eyetracking measures, see Clifton et al. (2007).

2.1.5 Predictions
Here, we briefly discuss key processing predictions for ambiguous RCs as
described by the above theories in terms of eye-tracking measures.
For integration-based processing effects, the process of integrating the filler
with its gap is predicted to occur at the head noun. For filler-gap parsing withinRCs, while this process can be observed as early as first-pass reading time, we
believe that regressive measures such as go-past time would better reflect the
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Ambiguity in Japanese95

both post-nominal (Gordon et al. 2006; Staub 2010; Staub et al. 2017) and prenominal languages (Kwon et al. 2010; Mansbridge et al. 2017a, 2017b), thismeasure has frequently been observed to occur at loci of integration. If thismeasure is greater for ORCs, this would indicate that the distance between thefiller-gap dependencies is greater than SRCs which would support the structuralmetric of integration (O’Grady 1997). If the reverse is found, it would support thelinear/temporal metrics (Gibson 2000; Lewis and Vasishth 2005).
Expectation-based processing accounts predict early difficulties within the
RC for the ORC condition prior to the reading of the head noun. Importantly,
these difficulties would occur prior to the clause-type disambiguation. Surprisal
theory (Levy 2008) would predict early-stage difficulty at the RC verb. At thereading of the RC verb, the contents of the RC would be interpreted as either amatrix clause with a subject pro-drop for SRCs or a matrix clause with an object
pro-drop for ORCs. Considering that the statistical probability for encountering
an object pro-drop is vastly lower than subject pro-drop, the ORC condition
would engender greater processing demands for the infrequent structure. The
same effect would also occur at the head noun when disambiguation of clausetype occurs but in terms of RC probabilities. Here, the SRC structure would havehigher expectation than the ORC structure. Following previous research investigating surprisal effects in RC processing, we predict that these difficulties would
be observed during the earliest stages of processing such as first-fixation duration and first-pass time. In a similar vein, the entropy-reduction hypothesis(Hale 2006) also predicts difficulties for the ORC condition prior to the readingof the head. As described above, this difficulty would occur upon the reading of
the case morpheme at the RC noun for ORCs. Considering that the difficulty
occurs at the morpheme, we believe that indications of this effect would be
revealed during first-pass time. Akin to surprisal, early difficulty at the headnoun is predicted for ORCs.
For similarity-based interference, predictions made by Gordon et al.’s (2001)
account is more variable than Lewis and Vasishth (2005). The former would
predict either early-stage or late-stage difficulty at loci where multiple similar
dependencies are stored (e.g. the head noun and RC noun) or loci where aretrieval for either of these dependencies would occur (e.g. the RC verb andmatrix verb). Difficulties could also manifest more generally within the sentence
due to the comprehension difficulties of maintaining two similar nouns. The
latter account, however, would only predict local difficulty at the matrix verb.
Because the effects are limited to the verb itself, first-fixation or first-pass reading would best reflect the difficulty.
Lastly, for the object-before-subject-bias (Nakamura and Miyamoto 2013),
difficulties would manifest at the head noun, RC verb and possibly the RC noun.

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96Michael P. Mansbridge and Katsuo Tamaoka

The difficulties within the RC itself would be encountered during later-stages ofprocessing as reflected by re-reading times and regression-in proportions. At thehead noun, however, it is not exactly clear at what time-frame difficulty would
occur. Considering that OBSB is described more of a repair process in theunderstanding of thematic roles, difficulty would likely be found during laterstages of processing such as re-reading, dwell time, go-past time and regressionout proportion.

2.2 Results
A series of linear mixed effect (LME) model analyses (Baayen et al. 2008) wereconducted on the collected reading times and binomial data (i.e. regression-in andregression-out proportion) using the lme4 package (Bates et al. 2014) within R (RCore Team 2015); the RC condition (ORC = −0.5 and SRC = 0.5) comprised the fixed
effects, and random effects were the subjects and items. Analyses of RTs andregression data only included items with correct responses. RT measures withzero RT or regions which were skipped were treated as missing values and were
not included in the RT analyses. The lmerTest package (Kuznetsova and Brockhoff2014) was used to provide RT models with p-values using Satterthwaite’s approximation for the degrees of freedom. For accuracy and regression proportions, glmer(binomial) within lme4 was used to calculate the z distribution using Laplaceapproximations. Data outliers (RTs only) were trimmed upon ± 2.5 standard deviations of each model (1.62 %) for better normality of residuals. Refer to Tables 1–2 formeans and LMEs. Refer to Figure 2 for plots of reading times.

2.2.1 Sentence
At the sentence level, there was a significant difference between RC conditions for
accuracy (p < 0.001) and the total reading time of the sentence (p < 0.05). It was
revealed that the questions for SRCs were answered more accurately, and the sentences overall were read more quickly for SRCs compared to their ORC counterparts.

2.2.2 RC noun
No eye-tracking index revealed a significant difference between RC conditions at
the RC noun. Accordingly, RCs did not differ substantially at this locus within
the RC.

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Ambiguity in JapaneseFirst-Fixation Time

Reading Time (ms)280First-Pass Time
475

ORC
SRC

425

260

375
240
325
220

275
225

200

Re-Reading Time
750
Reading Time (ms)

97

*

650

850

550
450

Dwell Time
1,050

*

*

650

*

450

350
250

250

Figure 2: Experiment 1 reading time plots.

2.2.3 RC verb
Only re-reading time ( p < 0.05) and dwell time ( p < 0.01) revealed that ORCs had
significantly longer reading times than SRCs. Because early measures did notreveal significant differences between conditions, these ORC difficulties reflectlate-stage difficulty at the RC verb and likely began after the clause wasdisambiguated.

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98Michael P. Mansbridge and Katsuo Tamaoka

Table 1: RC condition means of Experiment 1.
ORC
Mean

SRC
SE

ORC

Mean

SE

TT
ACC

,
.%

Sentence,.% .%


.%

FF
FP
RR
DT
GP
RO
RI






.%
.%N (RC Noun)










.% .%.% .%






.%
.%

FF
FP
RR
DT
GP
RO
RI

N (Head Noun)















.% .% .%.% .% .%






.%
.%

FF
FP
RR
DT
GP
RO
RI





,
.%
.%N (Matrix Object)









,
.% .%
.%
.%






.%
.%

Mean

SRC
SE

Mean

SE






.%
.%

V (RC Verb)










.% .%.% .%






.%
.%






.%
.%ADJ (Adjective)










.% .%.% .%






.%
.%





,
.%V (Matrix Verb)













,

.% .% .%

*
***

✝

✝
*
✝
✝

✝

*

*
**

*
✝

*

Note: p < 0.1†, p < 0.05*, p < 0.01**, p < 0.001***. Means and errors of reading times are displayed in milliseconds. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

2.2.4 Head noun
Only re-reading time (p < 0.05) revealed a significant difference between conditions:
ORCs had longer re-reading times at the head noun. While all other measures were

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Ambiguity in Japanese

99

Table 2: LME estimates and t/z values of Experiment 1.
SE

t/z valueTT
ACC

Sentence
–.
.
.
.

–.
.

FF
FP
RR
DT
GP
RO
RI

N (RC Noun)
–.
.
–.
.
–.
.
–.
.
–.
.
–.
.
.
.

–.
–.
–.
–.
–.
–.
.

FF
FP
RR
DT
GP
RO
RI

N (Head Noun)
.
.
.
.
–.
.
–.
.
–.
.
–.
.
–.
.

.
.
–.
–.
–.
–.
–.

FF
FP
RR
DT
GP
RO
RI

N (Matrix Object)
–.
.
–.
.
–.
.
–.
.
.
.
.
.
–.
.

–.
–.
–.
–.
.
.
–.

coef.

coef.

SE

t/z value

*
***

✝

✝
*
✝
✝

✝

*

.
< .
–.
–.
< .
.
–.

V (RC Verb)
.
.
.
–.
.
–.
.
–.
.
–.
.
.
.
–.

< .
–.
–.
–.
–.
–.
–.

ADJ (Adjective)
.
.
.
.
.
.
.

.
.
.
.
.
–.

V (Matrix Verb)
.
.
.
.
.
.
.
.
.
.
.
–.

–.
–.
–.
–.
–.
–.
–.

*
**

*
✝

*

Note: A positive estimate indicates an increase in reading time for SRCs. p < 0.1✝, p < 0.05*,
p < 0.01**, p < 0.001***. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

not shown to have significant differences between conditions, dwell time(p = 0.080) and regression-out (p = 0.075) had marginal tendencies for longer reading times and regressions made from the head noun for ORCs. In contrast, first-passtime (p = 0.069) showed a marginal trend for longer reading times within SRCs.

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100Michael P. Mansbridge and Katsuo Tamaoka

2.2.5 Adjective
At the second adjective which exists at the Head + 1 region (i.e. a spillover
region), the only significant difference between RC conditions was observed
during re-reading time ( p < 0.05) with ORCs necessitating longer re-reading
times than SRCs. No other measure had significant differences between conditions. Dwell time ( p = 0.095), though, revealed a marginal difference between
RCs, again showing longer reading times for ORCs.

2.2.6 Matrix NP-NOM object
Interestingly, regression-out proportion ( p < 0.05) revealed that there was ahigher probability for sentences containing SRCs to have a regression out of
the matrix object than sentences with ORCs. No other significant differenceswere seen.

2.2.7 Matrix verb
Regression-out proportion ( p < 0.05) was the only measure revealing a significant difference between conditions. Here, ORCs had a higher probability ofregressing out to other regions of the sentence.

2.3 Discussion
These results demonstrated greater ORC difficulties for ambiguous RCs, replicating the general findings from previous studies such as Ueno and Garnsey (2008).
However, this difficulty was only shown during later stages of processing (i.e.
re-reading time and dwell time) at the RC verb, head noun and the overallsentence. In the following sub-sections, ORC difficulty will be explained interms of each processing account.

2.3.1 Similarity-based interference
Ueno and Garnsey (2008) claimed that by using dative-topic case marking forthe head noun, the effects of similarity-based interference should be controlled.
As such, they argued that these effects are unlikely to contribute to the overall

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Ambiguity in Japanese101

difficulties with RC processing. However, that might not have been the case.
Despite the case markings being different between the RC noun and head noun,
the head noun can still be understood as the sentential subject with the othermatrix NP marked with nominative case understood as the object. In otherwords, the head noun might be a dative-subject while the other NP could be anominative-object. Thus, grammatical roles rather than case morphology might
have a more important role in causing similarity-interference. This explanation
would serve to explain why re-reading times and dwell times in particular werelonger for ORC conditions. Also, the increased regression-out ratio of the matrix
verb for ORCs fits into this interpretation. Accordingly, similarity-interference
should not be completely ruled out as a potential factor for ORC difficulty,
especially because it is compatible within the framework of Gordon’s similarity-interference account (Gordon et al. 2001).

2.3.2 Integration-based resources
The linear (Gibson 2000) and temporal distance (Lewis and Vasishth 2005)
metrics both predict SRC difficulty in Japanese, assuming the head noun integrates directly with the gap. The structural-phrase hierarchy metric, on the other
hand, predicts ORC difficulty. Because significant ORC difficulty was found at
the head noun, as in the previous studies, the only conclusion which could bemade is that decay increases as a function of structural-distance. Thus, thedistance between the head noun and gap is more local in terms of structuraldistance for SRCs. However, late measure effects such as re-reading are most
likely not indications of an integration/retrieval process. Typically, difficulties
with these processes are demonstrated by early-measures and regressive measures, yet none revealed any difference between RC conditions. Accordingly,
evidence for integration is only tacit as indicated by these results.

2.3.3 Expectation-based processing
Expectation-based processing (Hale 2001; Levy 2008) predicts ORC difficulty at
the head noun. Considering that these clauses were ambiguous up to the pointof the head noun, difficulty should not be observed until this locus. However,there was no immediate difficulty for ORCs at the head noun, and only late ORC
difficulty was observed at both the head noun and RC verb. Thus, even though
expectation-based processing predicts ORC difficulty, it does not seem to be thecase that the ORC difficulty here is a clear indication of expectation.

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102Michael P. Mansbridge and Katsuo Tamaoka

For the entropy reduction hypothesis (Hale 2006; Yun et al. 2015), though
ORC difficulty is predicted at the head noun as well, ORC difficulty should firstbe observed at the case morphology on the RC noun. However, ORC difficulty
was not observed at this region. Thus, entropy-based reduction is unlikely to
account for the ORC difficulty here. Yet, it could be the case that because only
case morphology acts as the cue to lower the entropy, the indices of processing
here were too coarse to reveal any difference.

2.3.4 The object-before-subject-bias
Considering that the head noun and RC verb both became more difficult for
ORCs during later measures of processing, this might reflect the greater difficulty in thematic assignment for ORCs in comparison to SRCs as Nakamura
and Miyamoto (2013) claim. In other words, after restructuring the clause at
the head noun, there is difficulty to assign the thematic role of the object head
and then the role for the RC subject thus increasing re-reading at the headnoun and RC verb for ORCs. But then again, it is still possible that working
memory, expectation and OBSB all contributed to the ORC difficulties in somefashion. Because only late-stage overall difficulties were found, it is hard to
attribute the difficulties to any single processing account or determine theirinterrelations.

2.3.5 Processing summary
Overall, it appears that participants were parsing the sentence without trouble
up to the head noun. Looking at the first-pass times in Figure 2, it can be seenthat there was a spike in first-pass time at the head noun for both RC types. It
is our interpretation that they experienced a garden path effect and had toreanalyse the clause from a matrix-clause to an RC which was taxing to theirparsers. As Nakamura and Miyamoto (2013) suggest, because of this misparse,
the contents of the RC might have been purged from working memory after thereading of the embedded verb. Accordingly, much effort was needed torestructure or reinterpret the clause. Despite this, it appears that participants
were likely to continue reading through the sentence as indicated by the low
regression-out proportions at the head noun. Note that this measure represents regressions made out during the initial first-pass. Rather than immediately reading back, participants seemed to finish reading the sentence andthen looked back at previous regions. Within these regressive readings, ORC

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Ambiguity in Japanese103

difficulties were centred on the RC verb and head noun. Because participants
were required to answer a post-sentence comprehension probe after reading
the sentence, these difficulties probably represent issues in comprehension,
particularly, the role of the head noun in relation to the RC argument. This canbe attributed to similarity-interference or issues of thematics for the RC argument. The former explanation is less credible as the head noun was an
adjunct-oblique rather than a clear subject; yet, in some cases the headmight nevertheless have been understood as a subject thus causing someinterference. The latter possibility appears to serve as a more suitable explanation. Because participants were going back and trying to remember thesentence, they had to re-construct the RC argument. This effectively makes
the parser subject to OBSB again during the re-reading of the sentence.

2.3.6 Ambiguity
Altogether, ambiguous RCs might not be the most suitable context to investigate
expectation- or memory-based processing models in Japanese. This is because
each RC condition involves a reanalysis of clause type. This can explain why
ORCs only became more difficult during later measures. In Experiment 2, we aim
to demonstrate that the disambiguation of clause type is a source of processing
difficulty at the head.
Considering that discourse-priming, successive case, clause-type plausibility, and numerical classifiers can all be slightly problematic methods to disambiguate the RC from a matrix clause interpretation initially, another methodof disambiguation should be used. In Japanese, there is one pre-RC cue which
has yet to be explored. That is pre-RC demonstratives. In Japanese, the demonstrative can either follow or precede the RC while still grammatically modifying
the same head noun (e.g. Ishizuka 2008). Following Kamio (1977; as reported
by Ishizuka 2008), if the demonstrative follows the RC, then the RC can haveboth a restrictive or non-restrictive RC interpretation while for pre-RC demonstratives only a restrictive RC interpretation is possible. See below for examples
from Kamio (1977: 153–154; as reported by Ishizuka 2008).
(10) a. Pre-RC demonstrative
その兄貴が買って来たりんご
Sono [aniki-ga katte-kita] ringothat brother-NOM buy-came apple‘that apple that brother bought’

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104Michael P. Mansbridge and Katsuo Tamaoka

b. Post-RC demonstrative
皆が探しているその論文[Minna-ga sagasiteiru] sono ronbun
everyone-NOM look.for that paper‘that paper, which everyone is looking for’By using this pre-RC cue, similar to that of Kahraman et al. (2014), theclause-type ambiguity can become disambiguated and a clause boundary
might be formed. There is one issue with this design however. Because thedemonstrative can also modify the RC noun, there is a chance that this condition
would still be ambiguous. Therefore, a word which cannot be modified by thedemonstrative must intervene between the two. Jäger et al. (2015) used a similartask design with determiner and classifiers in Mandarin Chinese. To prevent thedeterminer and classifier from modifying the RC noun, they inserted a temporaladverb at the start of the RC which would intervene between the two thus
preventing modification. Their findings revealed that this method was quite
effective at creating a clause boundary and effective at having the determinerand classifier modify the head of the RC. Thus, by using pre-RC demonstratives
and Jäger et al.’s (2015) design, RCs in Japanese should have attenuated ambiguity at the start of the RC. This will be explored in Experiment 2.

3 Experiment 2
The aim of the Experiment 2 was to compare RC processing under both ambiguous
and unambiguous contexts using the combined designs of Kahraman et al. (2014)
and Jäger et al. (2015): A pre-RC demonstrative article modifying the head noun
prior to the RC was inserted with a temporal adverb inserted at the start of the RC.

3.1 Methods
3.1.1 Participants
Forty (Female = 6) native Japanese speakers were recruited from a University inJapan. These participants were either undergraduate or graduate students at thetime of the study. The mean age was 19 years and 4 months; ranging from18 years and 2 months to 22 years and 11 months. None of the participants took
part in Experiment 1.

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Ambiguity in Japanese105

3.1.2 Materials
Thirty-two experimental items were created in a 2 (condition: SRC vs. ORC) by 2 (type:ambiguous vs. unambiguous) design. The items were put into counterbalanced lists
such that only eight items of each were shown per participant. For the unambiguous
types, a demonstrative modifying the head noun appeared at the sentence initial
position. To ensure that the demonstrative could not modify the noun in the RC, thedemonstrative was followed by a temporal adverb which blocked other interpretations. Additionally, an adverb also now intervened between the RC noun and RC
verb, and the matrix clause was expanded so that the first matrix predicate could
include regressive measures. For the ambiguous condition, the pre-RC demonstrative was simply not included. See below for RC examples. Eight practice and 72
distractor items were also included.
(11)

a. Subject-extracted relative clause (SRC)
その昨夜給仕さんを激しく襲った顧客は上司から聞いて、事件を伝えた。
Sono sakuya kyȗzi-san-o hagesiku osotta kokyaku-wa zôshi-kara kiite,
ziken-o tutaeta.
(that)[last.night customer-ACC fiercely hit]waiter-TOP boss-DAT heard
incident-ACC reported‘That waiter who fiercely hit the customer last night heard the boss andreported the incident.’b. Object-extracted relative clause (ORC)
その昨夜給仕さんが激しく襲った顧客は上司から聞いて、事件を伝えた。
Sono sakuya kyȗzi-san-ga hagesiku osotta kokyaku-wa zôshi-kara kiite,
ziken-o tutaeta.
(that)[last.night customer-NOM fiercely hit]waiter-TOP boss-DAT heard
incident-ACC reported‘That waiter who the customer fiercely hit last night heard the boss andreported the incident.’

3.1.3 Apparatus and procedure
The same apparatus of Experiment 1 was used in Experiment 2. The overall
procedure remained the same; however, feedback was provided after eachquestion as an attempt to improve accuracy scores. After a participant
responded to the verification question, feedback was automatically displayed

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106Michael P. Mansbridge and Katsuo Tamaoka

in the middle of the display which replaced the question with the feedback
message. The feedback displayed respective correct and incorrect messages inJapanese. By giving the participants feedback, we had hoped that participants
would become more involved in the task.

3.1.4 Predictions
Predictions for the processing of unambiguous RCs are given below.
The predictions for integration remained unchanged. We expected to findindications of integration during go-past times at the head noun.
The predictions made by expectation-based processing differ slightly for
unambiguous RCs. While pre-head difficulty is still predicted within surprisal
theory, the difficulty would reflect the greater surprisal for encountering the ORC
structure at the RC noun in comparison to the SRC condition. This is because thecase morpheme at the RC noun should act as a cue for the RC type. Thisdifficulty might also be seen at the RC verb where it is confirmed that no otherRC argument exists. These difficulties should be observed during early-stage
measures such as first-pass reading time.
The predictions for similarity-interference would remain unchanged from thepredictions for ambiguous RCs as multiple dependencies with overlapping features
still must be stored, maintained and retrieved throughout the reading of the sentence. Again, this might occur during both early and late measures of processing.
According to early accounts of OBSB, difficulties for the ORC condition are notexpected to occur because upon reading an unambiguous clause, there would begreater anticipation of the object’s role, thus attenuating difficulty. Consequently,
we do not expect to find evidence of this as indicated by our earlier predictions.

3.2 Results
The same LME procedures were repeated for Experiment 1. For the eye-tracking
data cleaning treatment, 8.44 % of eye-tracking fixations were trimmed during
the cleaning procedure. Ambiguous and unambiguous RC types were analysed
separately. RC condition composed the fixed effect and subject and items weretreated as random effects. RTs were log transformed and 1.51 % of the data wastrimmed. The following regions were analysed: the sentence as a whole, RC
noun, RC adverb, RC verb, head noun, matrix object, and matrix verb. Refer toTables 3–4 for means and standard errors and Table 5–6 for LMEs. See Figures
3–4 for plots of reading times (excluding go-past).

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107

Ambiguity in Japanese

Table 3: Ambiguous RC condition means of Experiment 2.
ORC
Mean

SRC
SE

ORC

Mean

SE

Sentence,.% .%


.%

*






.%
.%






.%
.%

**
**
**
***

TT
ACC

,
.%

FF
FP
RR
DT
GP
RO
RI






.%
.%

FF
FP
RR
DT
GP
RO
RI






.%
.%

V (RC Verb)










.% .%.% .%






.%
.%

FF
FP
RR
DT
GP
RO
RI

N (Matrix Object)















.% .% .%.% .% .%






.%
.%

Mean

N (RC Noun)





.%
.%

SRC
SE

Mean

SE

ADV

*

*
*

✝
✝
*






.%
.%






.%
.%






.%
.%






.%
.%






.%
.%

N (Head Noun)










.% .%.% .%






.%
.%






.%
.%V (Matrix Verb)










.% .%.% .%






.%
.%

***
**

✝

*

✝

Note: p < 0.1†, p < 0.05*, p < 0.01**, p < 0.001***. Means and errors of reading times are displayed in milliseconds. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

3.2.1 Sentence
Ambiguous: There were no significant differences between RC conditions forquestion accuracy, ( p = 0.275). However, the total reading time of the sentence

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108Michael P. Mansbridge and Katsuo Tamaoka

Table 4: Unambiguous RC condition means of Experiment 2.
ORC
Mean

SRC
SE

ORC

Mean

SE

Mean

SRC
SE

Mean

SE






.%
.%

ADV










.% .%.% .%






.%
.%

✝
*
*
✝

TT
ACC

,
.%

Sentence,.% .%


.%

FF
FP
RR
DT
GP
RO
RI






.%
.%N (RC Noun)










.% .%.% .%






.%
.%

FF
FP
RR
DT
GP
RO
RI






.%
.%

V (RC Verb)










.% .%.% .%






.%
.%






.%
.%

N (Head Noun)










.% .%.% .%






.%
.%

**
*

FF
FP
RR
DT
GP
RO
RI

N (Matrix Object)















.% .% .%.% .% .%






.%
.%






.%
.%V (Matrix Verb)










.% .%.% .%






.%
.%

*

*

*

Note: p < 0.1†, p < 0.05*, p < 0.01**, p < 0.001***. Means and errors of reading times are displayed in milliseconds. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

revealed significant differences between RC conditions ( p < 0.05). It wasobserved that ORCs had significantly longer RTs than SRCs.
Unambiguous: Again, differences in question accuracy were not significant
between conditions, ( p = 0.513). Additionally, the total reading time did not havesignificant differences between conditions as well ( p = 0.780).

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Ambiguity in Japanese

109

Table 5: Ambiguous LME estimates and t/z values of Experiment 2.
coef.

SE

t/z value

coef.

SE

t/z value–.
< .
–.
–.
< .
–.
–.

ADV
.
.
.
.
.
.
.

–.
–.
–.
–.
–.
–.
–.

Sentence
TT
ACC

–.
.

.
.

–.
.

*

FF
FP
RR
DT
GP
RO
RI

N (RC Noun)
–.
.
–.
.
–.
.
–.
.
–.
.
.
.
–.
.

–.
–.
–.
–.
–.
.
–.

**
**
**
***

FF
FP
RR
DT
GP
RO
RI

V (RC Verb)< .
.
–.
.
–.
.
–.
.
–.
.
.
.
–.
.

.
–.
–.
–.
–.
.
–.

FF
FP
RR
DT
GP
RO
RI

N (Matrix Object)
.
.
< .
.
–.
.
–.
.
–.
.
–.
.
–.
.

.
.
–.
–.
–.
–.
–.

*

*
*

✝
✝
*

N (Head noun)< .
.
.
–.
.
–.
–.
.
–.
–.
.
–.
–.
.
–.
< .
.
–.
–.
.
–.
V (Matrix Verb)
–.
.
–.
–.
.
–.
.
.
.
.
.
.
–.
.
–.
–.
.
–.
.
.
.

***
**

✝

*

✝

Note: A positive estimate indicates an increase in reading time for SRCs. p < 0.1✝, p < 0.05 *,p < 0.01 **, p < 0.001 ***. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

3.2.2 RC noun
Ambiguous: During first-fixation ( p < 0.01), first-pass ( p < 0.01), re-reading(p < 0.01) and dwell time (p < 0.001) measures, it was revealed that ORCs required
significantly longer RTs compared to SRCs. Regression-out (p < 0.05) on the other
hand, revealed that SRCs were significantly more likely to regress out.

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110Michael P. Mansbridge and Katsuo Tamaoka

Table 6: Unambiguous LME estimates and t/z values of Experiment 2.
coef.

SE

t/z value

coef.

SE

t/z valueTT
ACC< .
–.

Sentence
.
.

–.
–.

FF
FP
RR
DT
GP
RO
RI

N (RC Noun)< .
.
–.
.
.
.
–.
.
.
.
.
.
–.
.

–.
–.
.
–.
.
.
–.

.
.
–.
–.
< .
–.
–.

ADV
.
.
.
.
.
.
.

.
.
–.
–.
.
–.
–.

✝
*
*
✝

FF
FP
RR
DT
GP
RO
RI

.
< .
–.
–.
–.
–.
.

V (RC Verb)
.
.
.
.
.
.
.

.
–.
–.
–.
–.
–.
.

–.
–.
–.
–.
–.
–.
–.

N (Head noun)
.
.
.
.
.
.
.

–.
–.
–.
–.
–.
–.
–.

**
*

FF
FP
RR
DT
GP
RO
RI

N (Matrix Object)
–.
.
–.
.
–.
.
–.
.
–.
.
–.
.
–.
.

–.
–.
–.
–.
–.
–.
–.

.
.
.
.
< .
–.
.

V (Matrix Verb)
.
.
.
.
.
.
.

.
.
.
.
.
–.
.

*

*

*

Note: A positive estimate indicates an increase in reading time for SRCs. p < 0.1†, p < 0.05 *,p < 0.01 **, p < 0.001 ***. TT stands for Total Reading Time of the Sentence, FF stands for FirstFixation Duration, FP stands for First-Pass Time, RR stands for Re-Reading Time, DT stands for
Dwell Time, GP stands for Go-Past Time, RO stands for Regression-Out Proportion, and RI
stands for Regression-In Proportion.

Unambiguous: Only dwell time ( p < 0.05) was observed to have a significant
difference between RCs revealing that ORCs required overall longer RTs. The
remaining indices did not contain significant differences between SRCs and
ORCs.

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Ambiguity in JapaneseFirst-Pass TimeFirst-Fixation Time
300

450

Reading Time (ms)

ORC
SRC

275

250

*

400

*

350
300

225

250

200

200

Dwell Time

Re-Reading Time
1000

700

*

*
Reading Time (ms)

111

600
750
500

*

**

*

500
400

*
300

250

Figure 3: Experiment 2 ambiguous RC reading time plots.

3.2.3 RC adverb
Ambiguous: Both re-reading time ( p < 0.001) and dwell time ( p < 0.01) revealed
that ORCs required significantly longer reading times during later measures ofprocessing. However, dwell time here should only be considered to reflect thedifference in re-reading because early measures revealed no significant
differences.

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112Michael P. Mansbridge and Katsuo Tamaoka

First-Fixation TimeFirst-Pass Time
450

300

Reading Time (ms)

ORC
275

SRC

400

*
*

250

*

350
300

225

*

250

200

200

Dwell Time

Re-Reading Time
1000

Reading Time (ms)

700

*

600
750

*

500

400

300

*

500

250

Figure 4: Experiment 2 unambiguous RC reading time plots.

Unambiguous: Both first-pass reading time (p < 0.05) and re-reading time (p < 0.05)
were shown to reveal significant differences in reading times between RC conditions. However, while first-pass demonstrated longer reading times for SRCs, thiswas reversed for re-reading time. Also, during dwell time (p = 0.061), ORCs were
found to require marginally longer overall reading times compared to SRCs.

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Ambiguity in Japanese113

3.2.4 RC verb
Ambiguous: It was revealed that during re-reading ( p < 0.05) and dwell time
( p < 0.05) the ORC condition had significantly longer RTs. Other measures were
not observed to have significant differences between RCs.
Unambiguous: No index revealed a significant difference between RC conditions at the RC verb for unambiguous RC types.

3.2.5 Head noun
Ambiguous: Only dwell time ( p < 0.05) showed a significant difference between
RCs revealing that ORCs required longer overall RTs. Other measures were notobserved to have significant differences between RCs.
Unambiguous: First-fixation ( p < 0.01), first-pass ( p < 0.05) and dwell time
( p < 0.05) measures demonstrated that ORCs were read more slowly than SRCs at
the head. The remaining measures did not differ significantly between RCs.

3.2.6 Matrix object
Ambiguous: Only regression-out proportion ( p < 0.05) revealed a significant
difference between RC conditions; ORCs had a higher likelihood to regressout of the matrix object. While all other measures did not have significant
RC differences, go-past time ( p = 0.059) had a marginal trend showing that
ORCs had longer regressive reading times before moving on to the matrix
verb.
Unambiguous: No measure displayed significance between RC conditions.

3.2.7 Matrix verb
Ambiguous: No measure displayed a significant difference between RC
conditions.
Unambiguous: Surprisingly, first-fixation duration ( p < 0.05) revealed that
SRCs required significantly longer reading times than ORCs during the earliest
measure of processing at the matrix verb. However, this effect quickly diminished because no other measure of processing was significantly different
between RC conditions.

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114Michael P. Mansbridge and Katsuo Tamaoka

3.2.8 Post-hoc sentence completion task
We conducted a sentence completion task after the completion of the eyetracking study in Experiment 2. The sentence completion task is thought of asa technique to tap into production preferences of native speakers. Previous
studies concerning Japanese relative clause processing have conducted sentencecompletion tasks on their items to determine if an item set would elicit aparticular RC interpretation at a greater frequency than its counterpart. As
mentioned above, these investigations have often yielded conflicting results inJapanese. This is, however, not surprising when considering the statisticalproperties of various syntactic structures for Japanese. Specifically, while SRCs
are more frequent than ORCs, subject pro-drop is overwhelmingly more frequent
than object pro-drop (see Yun et al. 2015: 141). Thus, this creates a conflict inpredictions when a provided NP contains accusative case because both an RC
interpretation and a pro-drop interpretation have high preference biases. As
such, the reading up to the first verb is less constrained for the SRC condition
allowing for greater structural variance. In contrast, because object pro-drop is
infrequent in comparison to ORCs, it should be easier for participants to consider
the clause as an RC.
While the level of entropy or uncertainty in the fragment is higher for ORCs
at the embedded RC verb compared to SRCs (Yun et al. 2015: 136), the hierarchy
for the probabilities of the remaining structures would favour ORC interpretations. For each RC condition, although the structures with the highest probabilities are a matrix clause and an RC respectively, after these, structuralprobabilities begin to diverge. Importantly, for ORC fragments, the following
two structures are ORCs with varying syntax while for SRC fragments, thestructures are a complement clause and another SRC respectively. Thus, while
SRCs are more frequent than ORCs, the data collected from this task is unlikely
to reflect the overall distribution of RCs. Instead, the data will most likely reflect
the varying structural probabilities that are permissible in the ongoing structure.
In summary, if predictions for RC completions were to be based upon theoverall distribution of RCs or the ORC difficulties observed at the head noun
from the current and previous studies, then SRCs should be formed at a greater
percentage than ORCs. On the other hand, ORCs would be expected to occur
more frequently when considering the syntactic probabilities of the ongoing
structure.
Considering the issues discussed above, we primarily concerned ourselveswith whether the formation of an RC interpretation exceeded chance level. This
was to determine whether there were issues in item design that prohibited an RC
interpretation. The distribution of RC types was a secondary inquiry. Forty-four

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Ambiguity in Japanese115

native Japanese speakers, undergraduates at a Japanese University, wererecruited to participate in this task (N = 44, Female = 20). No subject participatedin either eye-tracking experiment. For the task, the items for Experiment 2 weremade into fragments such that the string ended at the RC verb. In order to notprime participants for an RC interpretation, the pre-RC demonstrative cue was
not included. Two counterbalanced lists were created, each containing 32 fragments. Half contained an accusative marked NP and the other half contained anominative marked NP. The ordering of fragments was also controlled so that
items of the same NP case marking would not repeat more than twice.
(12)

a. Subject-extracted relative clause fragment
昨夜給仕さんを激しく襲った
Sakuya kyȗzi-san-o hagesiku osotta[last.night waiter-ACC fiercely hit]‘(gap/pro) fiercely hit the waiter last night’
b. Object-extracted relative clause fragment
昨夜給仕さんが激しく襲った
Sakuya kyȗzi-san-ga hagesiku osotta[last.night waiter-NOM fiercely hit]‘the waiter fiercely hit (gap/pro) last night’

For this task, participants were instructed that they must complete the fragmentprovided to make it into a grammatical sentence. They were also instructed thatthey must provide at least one additional word and not end the sentence with anoun. For data collection purposes, we recorded whether participants created an
externally headed RC out of the fragment upon completing the sentence. See
below for examples.
(13)

a. Relative Clause – 1 (an RC)
昨夜給仕さんを激しく襲った顧客は逮捕された。
Sakuya kyȗzi-san-o hagesiku osotta kokyaku-wa taihosareta[last.night waiter-ACC twice hit] customer-TOP was.arrested‘The customer who fiercely hit the waiter last night was arrested.’b. Relative Clause – 0 (not an RC)
昨夜給仕さんを激しく襲ったと聞いた。
Sakuya kyȗzi-san-o hagesiku osotta to kiita[last.night customer-ACC twice hit] COMP heard‘(I) heard that (pro) fiercely hit the customer last night.’

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116Michael P. Mansbridge and Katsuo Tamaoka

The results of the sentence completion task were analysed using both chi-square
goodness of fit tests and LME methods. For this data set, if it was determinedthat the participant made the fragment into an RC upon finishing the sentence,
the item was given a value of 1, and if another structure was created, the item
was given a 0 value (i.e. binomial data). For the analyses to determine whether
RCs formations exceeded random chance, chi-square goodness of fit tests wereused. For the analysis comparing RC conditions, the glmer function within lme4
was used in R. The RC conditions comprised the fixed effect, and both subject
and items were treated as random effects with both random intercepts andrandom slopes.
The overall likelihood for participants to turn the fragments into RCs was
significantly greater than chance [X2 (1, N = 1408) = 192.05, p < 0.001] with RCs
obtaining 964 tokens. This was also true when analysing within both the ORC[X2 (1, N = 704) = 198.69, p < 0.001] and SRC [X2 (1, N = 704) = 30.28, p < 0.001]
conditions. ORCs received 539 RC tokens while SRCs obtained 425.
Accordingly, when prompted to finish a fragment with either a missing subject
or object, participants created RC structures at a rate exceeding random
chance. The rate of non-RC constructions among all completions slightly
differed from Ueno and Garnsey (2008): mono-clausal sentences (ORC: 1.3 %and SRC: 1.0 %), adjunct clauses (ORC: 6.0 % and SRC: 12.5 %), fact-clauses(ORC: 3.8 % and SRC: 5.7 %), and other clauses (ORC: 0.4 % and SRC: 0.4 %).
Specifically, while adjunct and fact-clauses were shown to have moreinstances in the SRC fragment category, the difference between conditions
for mono-clausal sentences diminished. Another notable difference was theuptake in adjunct clauses in the current study. Given the fragments, when notforming RC structures, participants preferred to form adjunct clauses and factclauses with pro-drop interpretations for both conditions.
Moving on to the glmer analysis, the results revealed that when participants
completed the fragments, the likelihood of the fragment being made into an ORC(Mean = 0.766, SE = 0.016) was much more probable than the fragment becoming
an SRC (Mean = 0.604, SE = 0.018); coefficient = −1.42, SE = 0.33, z = −4.31,
p < 0.001). To properly complete the task, participants did not have to commit
to an RC interpretation as there were a wide range of permissible structures, forinstance, complement and adjunct clauses. Accordingly, this result is consistent
with the above prediction that the ORC prefix string is more constrained to an RC
interpretation than its SRC counterpart, a point addressed by Yun et al. (2015)
and Ueno and Garnsey (2008). Briefly put, other syntactic options are more
permissible for the SRC condition. This finding, on the other hand, contradicts
with the overall distribution of RCs in the language (i.e. SRCs are more frequent

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Ambiguity in Japanese117

than ORCs) and the difficulties observed for ORCs at the head noun in thecurrent study and previous studies.
Overall, the sentence completion task data does not appear to relate to thedifficulties observed during sentence processing. Instead, the task seems well
suited at exploring the level of certainty in the ongoing formation of thestructure. Importantly, the degree of certainty might only engender difficulty
during on-line processing when entropy is reduced between words, Hale’s(2006) entropy-reduction hypothesis, or during the ongoing process of revising
structural expectations, Levy’s (2008) surprisal theory. However, we believe thatthe task has less conflict with the entropy-reduction hypothesis than surprisal
theory because, despite ORCs being more constrained, the overall reduction in
entropy would nevertheless be greater between the RC verb and head noun. In
contrast, if the data collected here and by other researchers were to be applied to
expectations during reading, it would suggest that there would be a lesser needto revise the structural expectations for ORCs compared to SRCs. Yet, the above
eye-tracking results directly contradict this. Thus, completions elicited by participants appear not to directly relate to the expectations native speakers generateincrementally during the reading of the structure but instead might relate moreto the certainty of the structure.
In conclusion, we advise caution using the sentence completion task to
predict Japanese native speakers’ expectations during reading. It neverthelessremains unclear which of the two expectation accounts applies to the participants’ on-line processing or if working memory is more heavily involved insentence processing than expectations. Another possibility is that there is a
general conflict between offline production and on-line reading data.
Specifically, the nature of the task might elicit participants to form other permissible structures to avoid repetition. What is apparent is that the items used inExperiment 2 had a high likelihood of activating an RC structure.

3.2.9 Post-hoc naturalness decision task
To determine whether a particular condition was more natural than the other, apost-hoc naturalness decision task was also conducted on the above stimuli.
Twenty (N = 20, Female = 12) native Japanese speakers were recruited froma Japanese University. All participants were undergraduate students, andnone took part in the above eye-tracking experiments or sentence completiontask. The experimental stimuli were separated into four counterbalanced lists
with each containing eight items for each RC and ambiguity condition. A
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118Michael P. Mansbridge and Katsuo Tamaoka

unnatural and + 3 being rated as most natural. Participants were instructed torate the items on the naturalness of each sentence, not grammaticality orplausibility. Each response was recorded as −3 to + 3 respectively. LME
models were used to analyse the data. RC condition and ambiguity typecomposed the fixed effects with subject and items as random factors. The
results revealed that there was a significant difference between RC condition(coefficient = 0.341, SE = 0.110, t = 3.09, p < 0.01) which demonstrated that SRCs
(Mean = 0.27, SE = 0.10) were rated more natural than ORCs (Mean = −0.72,
SE = 0.10). Similarly, there was a difference between ambiguity contexts(coefficient = 1.295, SE = 0.111, t = 11.67, p < 0.001) revealing that the ambiguous
context (Mean = 0.74, SE = 0.10) was more natural than the unambiguous
context (Mean = −0.54, SE = 0.09). There was no effect of interaction.
As mentioned, using pre-RC demonstratives should be quite unnatural.
However, it was the point of the design to use a context which would enhance
the RC interpretation. Because there was no interaction effect, we do not consider the use of the pre-RC demonstrative to be problematic.
In terms of relating the data found here with the above sentence processing
results, it might be the case that the naturalness of the sentences favoured the
SRC conditions during reading. Yet, the extent of this might not have far reaching consequences as processing differences were apparent between ambiguity
conditions during reading. Importantly, while unambiguous ORC sentences as awhole were not as difficult to process as unambiguous SRCs, it was the case thatambiguous ORCs had a higher overall processing cost than ambiguous SRCs.
Furthermore, for the ambiguous RC conditions, ORC difficulties were more widespread than the unambiguous condition. If the item naturalness greatly
impacted on-line processing, then its effect on processing would have likely
been more similar between ambiguity conditions. However, it is difficult toattribute item naturalness as the leading cause of ORC difficulty in both cases
because observations of ORC difficulty differed. Nonetheless, while we admitthat item naturalness might be a limitation of Experiment 2, the influence of
naturalness during on-line processing was likely minimal.

3.3 Discussion
Overall, Experiment 2 revealed greater ORC difficulties in the processing of RCs
by native Japanese speakers. Similar to the case in Experiment 1, ambiguous RCs
revealed ORC difficulties at the RC verb and head noun with additional difficulties observed at the RC noun. For unambiguous RCs, on the other hand, ORC
difficulty was chiefly limited to the head. In the following sections, each

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Ambiguity in Japanese

119

processing account will be addressed in relation to the data. Moreover, theinfluence of ambiguity will also be explored.

3.3.1 Similarity-based interference
For ambiguous RCs, similarity-based interference models (Gordon et al. 2001)
were supported at the RC noun, RC verb and head noun, i.e. the RC argument.
Because ORC heads and RC nouns had matching features, the ORC head could
retroactively interfere with the RC noun. Drawing on aspects of the objectbefore-subject-bias (OBSB) account (Nakamura and Miyamoto 2013), the prenominal RC structure requires the head of the ORC be integrated into thestructure before the assignment of theta to the subject. As such, similarityinterference occurring after the first reading of the RC agrees with OBSB.
Moreover, because a garden path effect exists up to the head noun, the entire
structure would need to be reanalysed, and this might induce comprehensiondifficulties for the RC argument due to the interference between nouns.
For unambiguous RCs, on the other hand, there were less indications ofsimilarity-based interference because difficulties were no longer shown at the RC
verb. However, it would be hasty to rule out interference effects altogether.
Essentially, having a head noun modified by a demonstrative might make thehead more distinct in working memory. If this reasoning is accurate, there
should be less proactive and retroactive interference between the NPs whichshould attenuate the interference effect.

3.3.2 Integration-based resources
According to linear/temporal distance metrics (Gibson 2000; Lewis and Vasishth2005), SRCs should be more difficult because the distance between the filler and
gap is more local for ORCs. In contrast, the structural distance metric predicts
the opposite. Because both ambiguous and unambiguous RCs produced ORC
difficulty at the head noun, the structural metric (O’Grady 1997) is better supported. Yet, we claim that neither case provided the crucial evidence for integration processes using eye-tracking. In the ambiguous context, ORCs were moredifficult during late measures while for unambiguous RCs this difficulty wasseen during early measures of processing. Even though some might suggest thatboth support a structural distance metric of integration, we claim that regressive
eye-tracking measures of processing, such as go-past time and regression-out
proportion, would better represent integration effects. Consequently, despite

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120Michael P. Mansbridge and Katsuo Tamaokathat the structural metric being supported here, we do not believe that it is thebest account for the ORC difficulties at the head noun.

3.3.3 Expectation-based processing
For ambiguous RCs, the first indication of greater ORC difficulty was found at
the RC noun as early as first-fixation duration. Considering that these clauses
were ambiguous and thus should be initially parsed as a simple matrix clausesentence, this finding goes against surprisal theory (Levy 2008) which would notnecessarily predict processing biases at this locus. This is because attestationaccounts for combined transitive and intransitive clauses are approximately
equal (see Yun et al. 2015). Yun et al. (2015), however, argued that difficulties
at the RC noun during early measures of processing are predicted by theentropy-based reduction hypothesis (Hale 2006). That is, there is greater reduction in entropy at the processing of a nominative case marker than an accusative
one. Notably, this finding conflicts with that of Experiment 1 which did notreveal any significant differences at the RC noun, let alone early measurementsof ORC difficulty. We address these differences in Section 4.1.1 below.
Nevertheless, similar to Experiment 1, ORC difficulty was observed at the RCverb and head noun during late-stage measures of processing. While expectation-based models (e.g. surprisal and entropy-reduction) predict ORC difficultyat the head noun, these models would be better supported if ORC significant
difficulties occurred during early-stage processing.
For unambiguous RCs, the first indication of early ORC difficulty was observedat the head noun which is a drastic shift in processing compared to the ambiguous
items of Experiment 1 and 2. We believe this change in processing to reflect thehigher activation level of the SRC structure. This was due to the additional cues todisambiguate the clause-type ambiguity. However, these cues did not allow theparser to utilize RC frequencies immediately for expectation purposes. Withinunambiguous RCs, there were no differences between RC conditions at the RC
noun which would serve as a potential cue for RC type due to case morphology.
Instead, ORC difficulty likely first occurred at the head noun (i.e. the locus ofdisambiguation) which suggests that the parser must have waited for a viable cue
to assign RC features to the clause, and only after this, differences between RC
conditions in terms of frequencies and expectation were observed.
Nonetheless, the additional cues were able to enhance the expectation of the
RC structure and likely increased the activation level for each structure. But
because SRCs are more frequent in Japanese, these cues had a greater benefit for
SRCs than ORCs.

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Ambiguity in Japanese

121

Moving on to the entropy-reduction model (Hale 2006), Yun et al. (2015)
claim the changes in entropy might be minimal for an unambiguous RC if thestructure is certain. This might explain why no difficulty was observed early at
the RC noun. However, following their rational, it is suspicious that there wasstill lingering difficulty at the head noun. It could be that while the cues
attenuated the ambiguity, there was still lingering uncertainty left in the structure which was subject to difficulties in entropy reduction between theembedded RC verb and head noun.
For the sentence completion task, ORC fragments were shown to have ahigher probability of having an RC structure formed than SRC fragments. As
argued above, this result is expected because ORCs fragments are more constrained to RC interpretations than SRC fragments, which explains why SRCs
were formed less often. Also, the findings of the sentence completion task do nottranslate well to on-line reading behaviour because ORC difficulty was primarily
observed. Thus, data collected from sentence completion tasks might not relate
to structural expectations during reading but instead reflect the degree ofcertainty for the structures which can complete the fragment. To clarify, theresults of the sentence completion task and the eye-tracking results might
support the entropy-reduction hypothesis more so than surprisal theory.
In general, expectation-based processing in languages like Japanese might be as
simple as a general advantage for transitive clauses which lack a subject in comparison to clauses lacking an object. Accordingly, regardless of the initial interpretation
made on an embedded clause, clauses lacking an object will likely be observed to be
more difficult to parse at the head due to revised expectations (Levy 2008) or the
reduction of entropy (Hale 2006) when using eye-tracking methods.
In summary, expectation-based processing models were shown to be satisfactory predictors of ORC processing for unambiguous RCs. When the RC structure became less ambiguous, expectation-based processing observations became
clearer and more robust.

3.3.4 The object-before-subject-bias
The results of Experiment 2 revealed that the general pattern for ambiguous
items was replicated when the items were strictly ambiguous. In other words,
the late processing difficulty was still observed for ORCs. This result provides
support for the object-before-subject-bias. Specifically, for ORCs after reading
the head noun, there were inherent difficulties involved in thematic assignmentfor RC arguments. This resulted in increased reading times during late-stage
measures at the RC noun, RC verb and head noun.

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122Michael P. Mansbridge and Katsuo Tamaoka

For unambiguous RCs, however, ORC difficulty was no longer observed at
the RC verb and the late difficulty for ORCs at the head noun was shifted toearlier measures of processing. Nakamura and Miyamoto (2013) suggested thatOBSB might not induce ORC processing difficulty for unambiguous RCs because
the head noun would be more anticipated. Miyamoto (2016), on the other hand,argued counter to this point and claimed that there would still be issues inthematic assignment. We argue along the lines of the earlier claim that OBSB
should not reflect the ORC difficulties of unambiguous RCs. If the RC structure isunderstood, then the thematic class of head noun should be able to be predicted
at the verb due to the collocations between the predicate and its direct object.
What is more, the attenuated ORC difficulty at the RC verb gives the impressionthat after reading the head noun there was less of a need to interface back withthe predicate to assign the theta role of the subject. In summary, we claim thatOBSB is a better predictor for ORC difficulty when the clause is ambiguous.

3.3.5 Processing summary
Our interpretation of participants processing for ambiguous RCs remained relatively unchanged. Only minor differences between experiments were present.
Most notably, early ORC difficulty was observed at the RC noun. This finding,however, is explained by the entropy-reduction hypothesis. As such, the difficulty found here most likely represents the processing work of eliminating
uncertainty in the structure. After this point, we do not consider the differences
between experiments to drastically change the overall processing behaviour
besides the increased re-reading at the RC noun for ORCs. As such, refer backto Section 2.3.5 for the processing pattern for ambiguous RCs.
For the processing of unambiguous RCs (i.e. attenuated ambiguity), thepattern of processing was quite distinct from ambiguous RCs. During the readingof the RC, it appears participants did not experience considerable difficulties.
Unlike the ambiguous RCs, we argue that here participants must have beenaware that they were reading within an embedded clause if not specifically an
RC. Unlike ambiguous RCs, the head noun did not induce RTs drastically forboth conditions in respect to the other regions. Instead, only ORC difficulty wasobserved at the head. However, this goes against our initial predictions that ORC
difficulty should be seen early at the RC noun or the RC verb. In fact, this shouldhave been the case regardless if a complement clause or an RC interpretation
was made. Consequently, the clause itself might lack its respective features until
the head, or participants adopted a wait-and-see approach to the understandingof the clause. While we argue that it is the former, the latter cannot be

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Ambiguity in Japanese123

completely ruled out. Regardless, once participants started reading the headnoun, they began to experience difficulties with ORCs. This is most likely
associated with issues in encountering an infrequent structure in respect to amore frequent one. After reading the sentence, we suspect that participants
again re-read the sentence to answer the following question. However, unlike
the ambiguous RCs, participants did not find one sentence type to be any moredifficult than the other. We attributed this to the attenuated similarity-interference effects as well as OBSB no longer being key processing factors.

3.3.6 Ambiguity
Comparing the effects of ambiguous and unambiguous RCs, there was a clear
change in processing behaviour. Importantly, processing changed at the headnoun. For the ambiguous RCs, the key results of Experiment 1 were replicated(i.e. general late ORC difficulties); however, for unambiguous RCs, ORC
difficulty was observed much earlier. As mentioned above, we consider thischange between conditions as an indication of expectation-based processing
becoming more prominent. In all, the expectation-based processing accountprovides the most suitable explanation for the results found in Experiment 2.
Because cues were introduced to eliminate the matrix clause interpretationand likely generated an RC interpretation, upon reaching the locus of disambiguation, the activation level for SRCs would have been much higher
than ORCs due to their higher frequency in corpora. Also, the parser would
be less bottlenecked by other processing factors such as OBSB and similarityinterference.

4 General discussion
The purpose of this study was to investigate how relative clause processing inJapanese unfolds as a factor of ambiguity. Particularly, we wished to investigate the validity of the object-before-subject-bias, memory-effects (i.e. integration and similarity-interference) and expectation-based processing withindifferent contexts of ambiguity. Overall, the results revealed that different
patterns of processing were associated with the different levels of ambiguity
found in each context: (1) ambiguous items had general ORC difficulty duringlater reading times and (2), when the head noun was modified by a demonstrative article preceding the RC, ORCs had longer reading times during early-

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124Michael P. Mansbridge and Katsuo Tamaoka

stages at the head noun. In general, processing was altered when there wasgreater anticipation for a head noun. In other words, when RCs were ambiguous, the object-before-subject-bias provided the best account for the ORC
difficulty, and when they were unambiguous, expectation-based processing
was better at predicting ORC difficulty. Below, we provide a summary for each
RC context.

4.1 Ambiguous relative clause processing
Within the processing of ambiguous RCs in Japanese, it appears the effects of
expectation-based processing and integration were masked or diminished.
Even though both accounts predict ORC difficulty at the head noun, theobservations found do not best reflect either account. While the surprisal
model (Levy 2008) predicts ORC difficulty at the head noun during disambiguation of clause type, this processing account would be better supported if
early-stage difficulty was also observed. For integration effects, we contend
that concrete evidence would be reflected by go-past times. Rather, only latestage difficulty was observed at the head noun. This can be attributed tomultiple processing demands occurring at the head, for example, a heavy
syntactic reanalysis and filler-gap parsing. These effects in tandem (and possibly others) would overload the processing bottleneck and diminish processing observations at this locus during early measurements of processing. As
noted earlier, when methods to attenuate the ambiguity are introduced, theprocessing burden at the head noun is attenuated as well. Consequently, SRCsand ORCs might only have subtle differences in observations of processing
when a heavy syntactic reanalysis is required.
While we contend that integration-effects were not conclusively supported
by our results, Ueno and Garnsey (2008) provided convincing evidence thatfiller-gap parsing is involved at the head noun. Although, as mentioned earlier,their results are also subject to interpretation. Assuming their results are indeed
reflective of the integration process, the differences between studies mightreflect the different degrees of sensitivity each method brings or other task
related influences. Importantly, ERP methods typically only allow for a serial
reading of the sentence, i.e. word-by-word at a fixed interval with no re-readingor preview while eye-tracking presents the sentence all at once and allows
re-reading, preview and skipping. Rather than saying that the studies disagreewith one another, it might be more appropriate to claim that each study introduces different insights into the processing of RCs in Japanese. Consequently,
we maintain that part of the processing difficulty for ORCs at the head is elicited

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Ambiguity in Japanese

125

by a long-distance gap dependency as revealed by Ueno and Garnsey (2008).
However, this was not clearly observed in the current study.
The object-before-subject-bias (Nakamura and Miyamoto 2013), on the other
hand, appears well suited to explain the ORC difficulty for ambiguous RCs in
Japanese. Within ambiguous RCs, processing difficulty was chiefly observed at
the head noun and RC verb during later stages of processing which is consistent
with the predictions made by OBSB. As such, the ordering of theta roles for the
RC argument allows SRCs to be easier to process because the object is integrated
first with the RC verb prior to the head noun. Conversely, ORCs are more difficult
because the parser is required to wait until the head noun to go back and assign
the theta role to the RC subject.
Along with OBSB, similarity-based interference (Gordon et al. 2001; Lewis
and Vasishth 2005) can also explain the extra processing demands for ORCs inboth experiments. This is particularly interesting because Ueno and Garnsey(2008) had attempted to control for the effect in their items by making the headnoun an oblique-adjunct with dative-topic case. Despite this, the head noun
might still have been interpreted as subject-like in some cases thus allowing forsome overlapping features between nouns. In Experiment 2, however, it shouldhave been much clearer that the head noun was the subject of the matrix clause.
In all, when multiple subject arguments were stored, there was greater difficultyin maintaining these arguments as well as retrieving a specific one from memory
which agrees more to Gordon et al.’s (2001) account of similarity-interference.
Overall, similarity-based interference should be considered as an interactive
factor in Japanese RC processing. To better control the influences of similaritybased interference in future studies investigating ambiguous RCs, we suggestthat researchers should use RCs modifying an indirect object as it might better
attenuate this effect. For instance, ‘The mailman delivered the letter to thereporter who criticized the mayor.’
In summary, the current study provides tacit support for expectation-based
processing and a structural integration (O’Grady 1997) and clearer support forthe object-before-subject-bias (Nakamura and Miyamoto 2013) and similarityinterference (Gordon et al. 2001; Lewis and Vasishth 2005) for the processing of
ambiguous RCs in Japanese. Importantly, the felicitous argument here would bethat these effects are collectively influencing the processing of Japanese RCs.

4.1.1 Differences between experiments
While we argue that the overall interpretation for the results do not differ
between the ambiguous RC items of Experiments 1 and 2 (i.e. late-stage ORC

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126Michael P. Mansbridge and Katsuo Tamaoka

difficulty supports the object-before-subject-bias), the eye-tracking results
slightly differed between them.
Notably, early-stage difficulty for ORCs was observed at the RC noun (N1) in
Experiment 2, and differences between RC conditions were more pronounced
during re-reading times in Experiment 2. We highlight possible explanations as
to why the two experiments differed below.
One explanation that might help reconcile the early-stage differences is theslight differences between stimuli. While both experiments used ambiguous RC
items, the contents of the items differed between experiments. Particularly, in
Experiment 1, the RC contents were composed of an adjective, a noun and averb, while in Experiment 2 they were composed of a temporal adverb, a noun,
another adverb and a verb. As such, one possibility is that moving from a
temporal adverb to a noun involves a different process than from an adjective.
Thus, it might be that participants in Experiment 2 preferred a subject-pro
instead of an overt subject whereas no such preference was held by the participants in Experiment 1.
While the difficulty of nouns marked with nominative case is often considered a typical observation in Japanese sentence processing, the entropy-reduction hypothesis considers the difficulty to reflect the greater reduction of entropy
between a noun and its nominative case marking compared to a noun and its
accusative marking. Thus, the early ORC difficulty at the RC noun in Experiment
2 might reflect this process. As to the reason why no difference was observed inExperiment 1, the possibilities could also reflect the above differences in items
which allowed the effect to be more pronounced in Experiment 2.
Also, the differences in the items’ naturalness might have allowed for
differences in reading behaviour between the two experiments to appear; yet,this is not the best explanation. As discussed above, if item naturalness was the
major cause of the discrepancies, then unambiguous items of Experiment 2
should have been more similar to the ambiguous items in terms of ORC
difficulties.
Concerning the difference during re-reading, another possibility is the minor
difference in experimental methodology. While the procedures were nearly
identical, there were two aspects that differed. First, more time was allotted
for reading the sentence due to the increase in item length for Experiment 2.
However, by comparing the overall total reading times of the sentences for each
ambiguous RC condition, the reading times for Experiment 1 were numericallylonger than Experiment 2. As such, giving more time to the participants did not
likely alter their reading behaviour. However, it is important to note that thelengths of the ambiguous items in Experiment 2 were longer than the item
lengths of Experiment 1. This oddity might be explained by the second difference

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in methodology, which is feedback. Specifically, in Experiment 1 feedback was
not given after the participant responded to the comprehension probe, whereas
in Experiment 2, it was. Again, by comparing the re-reading times of the RC
between experiments, Experiment 1’s re-reading times were also longer thanExperiment 2’s re-reading times for the regions within the RC. As such, one
could infer or speculate that without feedback, participants spent more time rereading the sentence prior to moving on to the question. In other words, this
could be construed as extra cognitive effort being given to prepare for the postsentence comprehension question during the reading of the stimulus. At the very
least, participants might have oriented their reading differently based on thepresence of feedback.
For both the early-stage and late-stage differences, another possibility is that
there is random variability among native speakers of Japanese. While theparticipants of both groups were primarily composed of undergraduate students,
their majors differed. Specifically, the ratio between agricultural, economics andengineering students differed between experiments as well as the distribution ofmale and female participants. Accordingly, there is some possibility that thedifferences among these small subsets of native Japanese speakers might represent the differences between the Experiments.
In summary, while the differences between the two experiments are noteworthy, we do not consider them to warrant major concern for the overall
interpretation of late-stage difficulty for ambiguous ORCs.

4.2 Unambiguous relative clause processing
In Experiment 2, we introduced an unambiguous RC context. Admittedly, theterminology ‘attenuated ambiguity’ would more appropriately describe the context. Because we believed that the parser is bottlenecked at the head noun for
ambiguous RCs, we inserted pre-RC demonstratives to eliminate a matrix clauseinterpretation and increase an RC one. Surprisingly, ORC difficulty was still
localized at the head noun rather than the RC NP which contained case morphology cues. However, a clear change of processing was nonetheless apparent
as difficulties were shifted from late-stage measurements to early-stage ones.
One argument could be made that the clauses were still ambiguous thus
making disambiguation obligatory at the head noun. However, we do notbelieve this to be the case. First, the results of our sentence completion task aswell as tasks in other studies reveal that RC structures are formed more often
than non-RC structures. Second, even if a non-RC interpretation was made, theORC condition should nevertheless be found to be more difficult, owing to the

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128Michael P. Mansbridge and Katsuo Tamaoka

fact that object-drop is far less frequent than subject-drop. Similarly, the attestation counts provided by Yun et al. (2015) would suggest that RCs would have ahigher rank in a probabilistic parallel parser in comparison to a complement
clause upon reading the transitive embedded verb. Third, considering that thecurrent study and previous studies (e.g. Miyamoto and Tsujino 2016) did not find
ORC difficulty prior to the reading of the head noun within unambiguous
contexts, our results are not dissimilar. In addition, studies for other prenominal
RC languages (e.g. Kwon et al. 2010; Mansbridge et al. 2017b) also found no
indications of immediate effects of expectation. Thus, even between languages,
similar patterns are found. Rather than being a locus of disambiguation, we
contend that the head noun here acts as a cue to assign the RC value to theclause and after this point the parser is susceptible to the influences of RC
probabilities.
Our rationale for this argument comes from recent findings in English by
Staub et al. (2018). In their study, they compared the processing of RCs againstcomplement clauses. Importantly, the key aspect of their study was that there
was ambiguity in one RC condition which would provide an incorrect complement clause interpretation for the RC (e.g. ‘The report that the senator prepared’vs. ‘The report that the senator was sick’). Using eye-tracking, they found that
despite the higher probability of forming an RC, RC conditions were insteadfavoured to have a complement clause interpretation. Drawing on aspects of theminimal chain principle (De Vincenzi 1991) such that the parser will not create afiller-gap dependency unless it is forced, they concluded that in contexts ofambiguity, a serial-based parser will take a non-RC interpretation until it isproven incorrect. This could of course be influenced by cues within the sentence
to force the RC interpretation earlier. Their argument, however, challenges theranked-parallel parser premise of surprisal (Levy 2008) and has severe implications for prenominal-RC languages. Specifically, unless strong cues are inserted,
disambiguation is likely to occur within both ambiguous and unambiguous RCs
at the same locus. This would help explain recent findings by Mansbridge et al.
(2017b) and Kwon et al. (2010). Importantly, both studies revealed expectationbased effects for unambiguous clauses at the predicted locus of disambiguation
for ambiguous RCs.
Unlike Staub et al. (2018), however, we do not believe that only a single
interpretation is permissible by the parser at a time. Instead we contend thatwhile interpretations are ranked, structural probabilities are also modulated byother processing principles, in this case the minimal chain principle. Within ourargument, we contend that the while structure is activated in the parser, thedifficulties in terms of expectation are not observed until a cue can assign
specific clause features to the structure. Importantly, this is because a

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Ambiguity in Japanese

129

processing bias should have been observed prior to the locus of disambiguation
regardless if the parser interpreted the clause as an RC or a complement clause,
not only for Japanese but Korean and Mandarin as well.
One difference between these prenominal languages is that the ORCs difficulties in Korean (Kwon et al. 2010) and Mandarin (Mansbridge et al. 2017b) werefirst observed prior to the head noun. The importance of this is that the entire
structure was not required to be parsed out for ORC difficulties to occur. We thus
can conclude that these effects are neither immediate nor terminal in regard toloci of ambiguity. It was instead the specifics of the Japanese language thatcaused this. Specifically, typical Japanese RCs have no markers while both
Mandarin Chinese and Korean have relativizers and adnominal markers prior
to the head.
Together, these prenominal languages differ with key post-nominal languages such as English and Russian such that relativizers in these post-nominal
languages are typically encountered upon entering the clause. This is importantbecause RC or other clause-type features can be assigned to the clause initially.
This explains why processing asymmetries can be observed at the first available
loci in these languages whereas it comes later for prenominal languages. As
such, it is our argument that for the parser to be sensitive to structural probabilities, a key element or cue is first required to be integrated into the structure.
This in turn would help the parser from forming committed expectations of astructure with filler-gap dependencies when other possibilities exist, importantly, even if RCs are more frequent in corpora.
As mentioned, however, we disagree with Staub et al. (2018) claim for a
serial-based parser. If that were the case, then the object/subject asymmetry inthe current study should not have altered substantially. Rather, it is our interpretation that structural probabilities were being activated prior to the headnoun for the unambiguous RC conditions. Because the matrix clause interpretation was eliminated, other embedded clause structures were being activatedthus increasing the activation level for RCs, regardless if complement clauses
were ranked higher or not. When the RC feature was assigned at the head noun,
there were greater gains in activation for the SRC structure owing to its higher
frequency. This in turn facilitated the early readings at the head for SRCs andinduced reading times for ORCs which have a structural dispreference. It is ouropinion that this interpretation is well suited at explaining the ORC difficulties
for unambiguous Korean and Mandarin RCs as well.
In all, for expectation-based processing, we believe that more investigations are needed. One issue that requires further clarification is to determine if
parsing is serial or parallel. This would be particularly important to determine
if a complement clause interpretation or an RC one is taken despite RCs being

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130Michael P. Mansbridge and Katsuo Tamaoka

the more frequent structure. Another important issue is to determine if all
possible structures are available immediately in the probabilistic parser, if
certain structural probabilities are only introduced after additional elements
are integrated into the string or if some other intricate process is involved. In
other words, it is important to determine the timing and manner for weighting
structural probabilities in the parser. As we see it, the results of the current
study, results of other prenominal languages and even results of post-nominal
languages have confused these matters. Our interpretation is that while multiple probabilities are weighted against one another during the parsing of astring, our sensitivities to these expectations are only realized when there is alink to our past experience. For this to occur, certain features of a structure
must first be parsed (i.e. bottom-up processing) in order to determine if thecurrent string agrees with the expectations drawn from past exposure (i.e. topdown processing).
Moving on to effects of integration, while it is likely that such effects
occurred during the processing of these sentences, conclusive evidence waslacking. While the early reading times at the head noun can also represent theprocess of integration, it is hard to make a definite claim without differences
within regressive eye-tracking measures. As mentioned, the structure ofJapanese RCs is debated, and the possibility remains that Japanese RCs mightlack gaps. However, considering ERP evidence and evidence found in similar
languages such as Korean, we do not believe this to be the case. In order toresolve this issue, more studies are needed that focus solely on the integration
process in Japanese.
Another memory-based component of processing not observed during thereading of these unambiguous RCs was similarity-interference. Despite the head
and the RC noun having clearer overlapping features than in Experiment 1, nolate ORC difficulties were observed, and ORC difficulties were lacking at thematrix verb. However, this finding is not surprising because these heads wereadditionally modified by the demonstratives which could have caused the parser
to be less susceptible to interference effects. Similarly, Staub et al. (2017) also
reported reversals in ORC difficulties when ORC included an extra prepositional
phrase intervening between the RC verb and matrix verb. To explain this, theyargued along the framework of cue-based retrieval (Lewis and Vasishth 2005)
such that repeated activations on an item increase the activation level thus
making it more distinct in memory. For their study, the extra activations
occurred during the reading of the prepositional phrase, while it occurred during
the reading of the demonstrative in ours. Additionally, this could help explain
the lack of clear observance of integration-based effects here. Specifically, theadded modification could have caused an antilocality effect during the later-

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Ambiguity in Japanese131stages of processing. Overall, we find the diminished effects of interference to be
similar between languages.
Lastly, we will discuss whether the object-before-subject-bias is relevant forthe processing of unambiguous RCs. Interpreting OBSB for unambiguous RCs is
problematic because Nakamura and Miyamoto (2013) first claimed that OBSB
might not account for ORC difficulty if the clause is unambiguous while
Miyamoto (2016) claimed that the model still applies for unambiguous clauses.
Thus, there seems to be disagreement. Yet, considering that the unambiguous RCs
in Experiment 2 did not reveal ORC difficulty at the RC verb, it appears that OBSB
was no longer a factor. If it was, the parser would revisit and interface with the RC
predicate to assign the theta role, but no evidence for this was shown. Instead, theresults suggest that upon the initial reading of the sentence, there was no longer
any difficulty in terms of assigning the theta roles to the RC arguments. We
contend that this arises from greater anticipation of the subject’s role in the
ORC condition when a clause boundary is formed prior to the first reading.
In summary, the findings for unambiguous RC processing in Japanese support expectation-based processing and again provides tacit support for integration. However, both similarity-interference and OBSB were less supported forunambiguous RCs.

5 Conclusion
We conclude that clause type ambiguity is an integral factor in Japanese relative
clause processing. Furthermore, eliminating this ambiguity had great impact on
the processing of the sentence, particularly at the head noun as predicted. When
the RC was ambiguous, ORCs were more difficult to process after disambiguation, possibly due to the inherent difficulty of assigning thematic roles when
the object appears outside the clause as object-before-subject-bias predicts. Yet,at the same time, other processing factors such as expectation, structuralintegration and similarity interference were also supported because all predict
ORC difficulty. Thus, for ambiguous RCs it is challenging to attribute ORC
difficulties to any individual account listed above. In contrast, when the RC
was unambiguous, ORCs experienced early difficulty at the head noun. We
attribute this as a factor of expectation-based processing. Specifically, withattenuated difficulty and increased cues for the RC interpretation, expectationbased processing effects became more observable. In conclusion, this study
adds to the growing body of literature showing that expectation-based processing is a key factor for unambiguous RCs.

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132Michael P. Mansbridge and Katsuo Tamaoka

Acknowledgements and funding: We would like to extend our appreciation andgratitude to our reviewers and editor whose insightful comments and suggestions strengthened this article. We would also like to thank the participants ofthe 22nd Architectures and Mechanisms for Language Processing conference, the26th Conference of European Second Language Acquisition, and the 1st
International Conference on Theoretical East Asian Psycholinguistics for their
feedback concerning this research. Lastly, we would like to express our appreciation to Professor Masatoshi Sugiura of the Graduate School of International
Development at Nagoya University for allowing us to use his lab’s eye tracker.
This study was funded in part by the Japan Society for the Promotion of Science(JSPS) Grand-In-Aid for JSPS doctoral course fellows granted to Michael P.
Mansbridge, Grant Number 15J03336.

Compliance with ethical standards
No authors had a conflict of interest. All personal information collected fromparticipants was stored in a secured location, and participants were given
numerical pseudonyms for data analysis purposes to ensure privacy.
Participants were not subject to harm and could have only experienced mild
discomfort from prolonged seating or reading. Participants were allowed to takeshort breaks to prevent discomfort. In the current study, all participants firstgave informed consent prior to the experimental sessions. After the completionof the eye-tracking sessions and the sentence completion task, all participantsreceived monetary compensation. For the naturalness decision task, participants
partook in the survey on a voluntary basis, thus they did not receive monetarycompensation.

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