Journal of Neurolinguistics 47 (2018) 1–15

Contents lists available at ScienceDirect

Journal of Neurolinguistics
journal homepage: www.elsevier.com/locate/jneuroling

Individual mentalizing ability boosts ﬂexibility toward a linguistic
marker of social distance: An ERP investigation

T

Sachiko Kiyamaa,∗, Rinus G. Verdonschotb, Kexin Xiongc, Katsuo TamaokadaDepartment of Linguistics, Graduate School of Arts and Letters, Tohoku University, 27-1 Kawauchi, Aoba-ku, Sendai, Miyagi 980-8576, Japan
Department of Oral and Maxillofacial Radiology, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku,
Hiroshima, Hiroshima 734-8553, Japanc
Department of Teaching Japanese as a Foreign Language, Graduate School of Languages and Cultures, Nagoya University, B4-4 Furo-cho, Chikusaku, Nagoya, Aichi 464-8601, Japand
Department of Teaching Japanese as a Foreign Language, Graduate School of Humanities, Nagoya University, B4-4 Furo-cho, Chikusa-ku, Nagoya,
Aichi 464-8601, Japanb

AR TI CLE I NF O

AB S T R A CT

Keywords:
Interpersonal distance
Sentence-ﬁnal particle
Japanese
ERP
Early posterior negativity
Mentalization

Sentence-ﬁnal particles (SFPs) as bound morphemes in Japanese have no obvious eﬀect on thetruth conditions of a sentence. However, they encompass a diverse range of usages, from typical
to atypical, according to the context and the interpersonal relationships in the speciﬁc situation.
The most frequent particle, -ne, is typically used after addressee-oriented propositions for information sharing, while another frequent particle, -yo, is typically used after addresser-oriented
propositions to elicit a sense of strength. This study sheds light on individual diﬀerences among
native speakers in ﬂexibly understanding such linguistic markers based on their mentalizing
ability (i.e., the ability to infer the mental states of others). Two experiments employing electroencephalography (EEG) consistently showed enhanced early posterior negativities (EPN) for
atypical SFP usage compared to typical usage, especially when understanding -ne compared to-yo, in both an SFP appropriateness judgment task and a content comprehension task.
Importantly, the amplitude of the EPN for atypical usages of -ne was signiﬁcantly higher inparticipants with lower mentalizing ability than in those with a higher mentalizing ability. This eﬀectplausibly reﬂects low-ability mentalizers' stronger sense of strangeness toward atypical -ne usage.
While high-ability mentalizers may aptly perceive others' attitudes via their various usages of -ne,low-ability mentalizers seem to adopt a more stereotypical understanding. These results attest to
the greater degree of diﬃculty low-ability mentalizers have in establishing a smooth regulationof interpersonal distance during social encounters.

1. Introduction
Many people are sensitive to subtle cues in the behavior of others and can use those cues to ﬂexibly recognize social distance, or shared
psychological space with others. However, those without this sensitivity often fail to accomplish this delicate regulation, which might cause
awkward or even unpleasant feelings toward others. These individuals may therefore experience a certain sense of discomfort when creatinginterpersonal relationships. Indeed, there seem to be inter-individual diﬀerences in the sensitivity to others' cues that typically manifest in
nonverbal behavior, such as facial expressions (e.g., John & Gross, 2004) and gestures (e.g., Rosip & Hall, 2004).

∗

Corresponding author.
E-mail addresses: skiyama@tohoku.ac.jp (S. Kiyama), rinusverdonschot@gmail.com (R.G. Verdonschot), xiongkexinkuma@gmail.com (K. Xiong),tamaoka@nagoya-u.jp (K. Tamaoka).
https://doi.org/10.1016/j.jneuroling.2018.01.005
Received 18 December 2016; Received in revised form 19 January 2018; Accepted 30 January 2018
Available online 14 February 2018
0911-6044/ © 2018 Elsevier Ltd. All rights reserved.

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In addition to nonverbal behavior, language also plays a key role in controlling interpersonal distance. This seems particularly
evident in (spoken) Japanese, which has sentence-ﬁnal particles (SFPs) as bound morphemes such as -ne and -yo that uniquely serve
to indicate the interpersonal distance between addresser and addressee (Kamio, 1994; Katagiri, 2007). It is not uncommon for someEast and South-East Asian languages, like Mandarin Chinese (Li & Thompson, 1989), Cantonese (Matthews & Yip, 1994), Korean (Koo
& Rhee, 2013), and Malay (Neeleman & Szendröi, 2007), to have SFPs that can be attached after a predicate to specify the addresser's
attitude to the proposition to yield various discourse functions.
In Japanese, SFPs as function words have no obvious eﬀect on the truth conditions of a sentence (Davis, 2009), but they encompass a complicated and diverse range of usages, from typical to atypical, according to the context and the interpersonal relationships (Tanaka, 2000). The most frequent SFP, -ne, indicates the addresser's attitude that the stated proposition before the SFP
belongs to or is under the control of the addressee, while the second most frequent SFP, -yo, indicates that said proposition is under
the control of the addresser (Takiura, 2008). Accordingly, it is typical to attach -ne to sentences with addressee-oriented propositions
to communicate information shared with the addressee, and to use -yo for addresser-oriented propositions to elicit a sense of strength
or insistence (e.g., Kamio, 1994; Davis, 2009; see Table 1 for examples). Nevertheless, the opposite combinations, namely, an addresser-oriented -ne and an addressee-oriented -yo, are still grammatical and sporadically used, even though they are mostly atypical.
In an atypical usage of the addresser-oriented -ne, the addresser would create a somewhat “unfriendly attitude,” as if leaving the
given proposition to the addressee (Takiura, 2008). Participants in Japanese conversations are expected to detect these ﬂuid anddelicate senses intended by addressers through the use of SFPs, which are said to have chameleon-like qualities (Tanaka, 2000).
Several linguists studying Japanese SFPs (e.g., Cook, 1990, 1992; Maynard, 1994, 1997; Mizutani & Mizutani, 1987, among manyothers) have pointed out that -ne, being an addressee-oriented particle, typically plays an emotional role in that it helps to build arapport between the addresser and the addressee as it achieves information sharing. In contrast, the addresser-oriented function of-yo, meant to elicit a sense of strength, serves to emphasize the addresser's will or judgment. With these basic functions, Japanese
SFPs can arouse both pleasant and unpleasant emotions in the addressee. For example, an addressee would typically have a pleasantemotion if a favorable addresser used -ne to create empathy with the addressee because, in this case, the use of -ne would agree withthe addressee's expectation of closeness to the addresser. However, if a disliked person used -ne in succession, the addressee might
have an unpleasant emotion because, in this case, the addresser would give the impression of being overly familiar with or too
dependent on the addressee, who does not want to create empathy with the addresser. Indeed, Japanese SFPs are predominantly used
in informal face-to-face conversations and hardly appear in formal situations, such as court sessions and press reports, in which
addressers are not supposed to convey any emotion in order to stay neutral and objective with their message in front of an unspeciﬁed
audience. In sum, indications of interpersonal relationships through SFPs can unintentionally evoke various emotional reactions.
Japanese SFPs, therefore, seem to function as a set of inherent, pre-lexical interactional markers for native Japanese speakers,
independent of understanding the proposition itself. This is supported by the observation that typically developing Japanese children
begin to utter -ne at the age of two (i.e., the very earliest stage of language acquisition, during which children begin to make two-wordutterances) without explicit guidance from adults (Kajikawa, Amano, & Kondo, 2004; Shirai, Shirai, & Furuta, 2000). They evenoccasionally utter -ne by itself just to create empathy, even when they do not understand what the adult addresser is saying.
If SFPs' emotional function proceeds through the link with interpersonal distance, the understanding of Japanese SFPs likely
depends on the individual addressee's ability to imagine the addresser's thoughts and feelings. This can be referred to as a “theory ofmind” (ToM) or a “mentalizing” ability (Baron-Cohen, 1995). While mentalizing ability predicts others' behavior based on theirmental states, its more advanced features include knowledge about the emotional experience of others (e.g., Hooker, Verosky,
Germine, Knight, & D'Esposito, 2008). Although most native speakers seem to naturally acquire a sense of SFPs (Shirai et al., 2000),
Japanese children with high-functioning autism, who experience the greatest diﬃculty in solving mentalizing problems, seldom use
the rapport-creating SFP -ne (Watamaki, 1997). This observation is consistent with autistic children's pervasive pragmatic deﬁcits,
which can be characterized in terms of a lack of ability to share information or diﬃculty with diﬀerentiating addresser-addressee
roles (Baltaxe, 1977). Baron-Cohen (1988) argues that the pragmatic deﬁcits in autism derive from an innate inability to engage
emotionally with others, as well as an impairment of the meta-representation of attributing others' beliefs to their behavior. Amongtypical speakers, it could also be assumed that those with a lower mentalizing ability are more deﬁcient in understanding the SFP -ne,since the degree of mentalization ability follows a continuous distribution across the general population (Constantino & Todd, 2003).
To our knowledge, however, there is only limited experimental evidence available concerning how native Japanese speakers can
ﬂexibly recognize the large variety of usages that these SFPs allow, and to what extent the cognitive and aﬀective aspects of anindividual's mentalizing ability are associated with this ﬂexibility.
To elucidate the correlation between the ﬂexibility to successfully understand SFPs and an individual's mentalizing ability,
physiological indices such as event-related potentials (ERPs) are informative, as they have been found to disclose some of the courseof the involuntary processes of mentalization (see: Abell, Happé, & Frith, 2000). From a neurolinguistic perspective, one could expect
an N400 component (a negativity between 250 and 500 ms after stimulus onset in the centroparietal regions) to emerge in response to
an atypical usage of SFP -ne, as opposed to its typical usage. Since Kutas and Hillyard (1980) ﬁrst reported the eﬀect, numerous otherstudies (see Kutas & Federmeier, 2011 for a review) have shown that the classical index occurs in response to anomalies during the
integration of semantic information presented in sentence and discourse context. A similar N400 eﬀect has already been shown in
discourse comprehension in Japanese (Hirotani & Schumacher, 2011) and in pragmatic function words such as/cai2/and/jiu4/in
spoken Chinese (Liu, Jin, Li, Li, & Wang, 2009). Moreover, a correlation between the pragmatic N400 eﬀect and individual mentalizing ability is discernible (Nieuwland, Ditman, & Kuperberg, 2010), with high-ability mentalizers showing a larger N400 amplitude in response to under-informative statements than to informative statements.
However, we must note that the Japanese SFP -ne is qualitatively diﬀerent from pragmatic function words (Liu et al., 2009) and2

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Table 1
Example usages of Japanese sentence-ﬁnal particles -ne and -yo.

Notes: The abbreviations represent the following: DAT [Dative case marker], NMLZ [Nominalizer], COP [Copula], NOM [Nominative
case marker], SFP [Sentence-ﬁnal particle], PST [Past], LOC [Locative case marker]. Atypical markers appear between parentheses.

discourse comprehension (Hirotani & Schumacher, 2011; Nieuwland et al., 2010), which have been shown to induce an N400 eﬀect.
As discussed earlier, Japanese SFPs are considered to be more emotionally arousing linguistic markers of interpersonal distance,
unlike discourse markers such as the Chinese function words/cai2/and/jiu4/, which were examined by Liu et al. (2009).
Emotional processing and evaluation of interpersonal relationships could induce earlier ERP eﬀects, especially in those with alower mentalizing ability (or those with autistic traits; Orekhova & Stroganova, 2014; Perry, Levy-Gigi, Richter-Levin, & ShamayTsoory, 2015). Among early ERP components, an early posterior negativity (EPN) arising between 150 and 400 ms after stimulus
onset over the occipito-parietal cortex has been reported to reﬂect autistic individuals' emotion recognition and perceptual attention(Faja, Dawson, Aylward, Wijsman, & Webb, 2016). Several previous investigations have identiﬁed this component as relevant to thecomprehending of emotional words (e.g., Kissler & Herbert, 2013; Scott, O'Donnell, Leuthold, & Sereno, 2009; Zhang et al., 2014), as
well as the processing of non-linguistic stimuli such as scenes, faces, and gestures (e.g., Junghöfer et al., 2004; Schacht & Sommer,2009). EPN was initially linked to visual processing (see Schupp, Flaisch, Stockburger, & Junghöfer, 2006 for a review), but it has also
been demonstrated within the auditory modality (e.g., Jaspers-Fayer, Ertl, Leicht, Leupelt, & Mulert, 2012; Schupp, Junghöfer,Weike, & Hamm, 2003). Speciﬁcally, Mittermeier et al. (2011) found an inﬂuence in the EPN of individual personality traits, on thescale of extraversion-introversion, during an auditory choice task that entailed emotional intonation, with extraverted participants
having stronger EPN amplitudes for emotional words than for neutral words. This suggests that neural reactivity occurring in an
earlier time window may reﬂect a pre-lexical attentional processing stage that facilitates subsequent semantic integration (Kissler &Herbert, 2013). This idea is also supported by behavioral evidence showing that lexical decisions are made more quickly for emotional words than for neutral words (Kousta, Vinson, & Vigliocco, 2009). Following this logic, understanding auditorily presented
Japanese SFPs, which are emotionally arousing markers of interpersonal distance, may evoke some earlier potentials before N400.
So far, neural correlates of understanding SFPs with an individual's mentalizing ability have not been reported. Whatever thepolarity, some earlier ERP eﬀects might be induced, as the time course should be sensitive to the understanding of interpersonal
relations through those markers. The predictions of this exploratory study are therefore that 1) the understanding of Japanese SFPs
elicits a stronger EPN eﬀect in atypical than in typical usages, and 2) an individual's mentalizing ability inﬂuences this eﬀect. To
examine these predictions, we investigated whether ERP amplitudes correlated with native Japanese speakers' mentalizing ability
while understanding the auditorily presented SFPs -ne and -yo in typical and atypical usages. This was carried out while participants
made judgments of SFP appropriateness (Experiment 1), and while attempting to comprehend the content of the dialog with no
explicit instruction regarding SFPs (Experiment 2).
2. Experiment 1: SFP appropriateness judgment task
To examine native speakers' explicit judgments of sentences including Japanese SFPs, participants were required to judge whether
a given SFP was appropriate or not in the various presented dialogs (in what will be referred to as the appropriateness judgment task).
2.1. Materials and methods
2.1.1. Participants
Twenty-one healthy right-handed graduate and undergraduate students (12 males; age range: 19-24, M = 20.0, SD = 1.4) participated in Experiment 1 after giving informed consent in accordance with the Declaration of Helsinki. All the participants were
native Japanese speakers and reported to have no neurological problems. All of them were paid for their participation. This study wasapproved by the Ethical Committee of the Graduate School of Languages and Cultures, Nagoya University, Japan.
To assess the degree of each participant's mentalizing ability, participants were asked to complete the Japanese standardized
version of the Autism-Spectrum Quotient (AQ; Wakabayashi, Baron-Cohen, Wheelwright, & Tojo, 2006). This questionnaire has beenvalidated as an instrument for rapidly quantifying where an individual is situated along a continuum of autistic traits as diagnosed by
the presence of repetitive behaviors and limited imagination of others' mental states (American Psychiatric Association, 2013) in
adults with normal intelligence (Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001). We used AQ scores because they
have been shown to represent mentalizing ability within the general population (Baron-Cohen, Jolliﬀe, Mortimore, & Robertson,3

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1997; Nieuwland et al., 2010). The average AQ score (with higher scores indicating a lower mentalizing ability) among Japanese
university students (n = 1050) has been reported to be 20.7 (SD = 6.4) out of the maximum score of 50 (Wakabayashi et al., 2006).
For our participants in Experiment 1, the AQ total score ranged from 13 to 32 (M = 20.3, SD = 5.2), nearly equivalent to the overall
average of Japanese university students as reported by Wakabayashi et al. (2006).
2.1.2. Materials
The stimulus materials were auditorily presented dialogs speciﬁcally created for this study. First, 176 dialogs between two people
were prepared (i.e., small fragments of conversation as opposed to single sentences by one person), including the target SFPs -ne and-yo. To create the context necessary for judging the typicality of the SFP, each dialog consisted of two turns, with -ne or -yo at the endof the second turn. As shown in Table 1, the subject of each second turn was omitted, as Japanese is a pronoun-dropping (pro-drop)
language (Iwasaki, 1993). We manipulated the typicality of -ne and -yo in terms of whether the second turn concerned addresseeoriented content (i.e., a typical -ne and an atypical -yo) or addresser-oriented content (i.e., a typical -yo and an atypical -ne). We also
prepared 36 additional ﬁller dialogs, which presented topics general to both persons (i.e., neutral topics such as the weather or topics
pertaining to a third person). In these, either the grammatical combination -yone or the ungrammatical -neyo was used at the end of
the second turn.
All the stimulus dialog sets were recorded by a male (for the ﬁrst turn) and a female (for the second turn) native speaker ofJapanese, and they were saved as WAV sound ﬁles using PRAAT version 5.1.31 (Boersma, 2002). The recording was conducted turnby turn in as much of the same manner as possible, instead of splicing separately recorded parts of each turn, so that each turn would
sound seamless and natural (Fig. 1). To verify whether SFP typicality was successfully manipulated in the auditory stimulus materials,
26 native Japanese speakers (16 males; age range: 19-23, M = 20.0, SD = 1.2), who did not take part in any of the EEG experiments,
were randomly presented with the 176 candidate dialogs (including target and ﬁller stimuli). These Japanese speakers rated theappropriateness of the SFPs presented in each dialog on a seven-point scale (1: very inappropriate to 7: very appropriate). Based on
the results of the pilot test, we selected 80 dialogs, in which the mean diﬀerence between typical and atypical usage of a target turnwas greater than two. The ratings of the selected items revealed that turns intended as typical usages of an SFP (M = 6.32, SD = 0.37)
were signiﬁcantly more appropriate than those intended as atypical usages (M = 2.96, SD = 0.48, t78 = 34.529, p < .001,
d = .423). Another 36 ﬁller dialogs with various content were included for the ERP experiments. All target and ﬁller dialog sets (andtheir English translations) are provided as supplementary data.
To ensure that speech prosody was not signiﬁcantly diﬀerent between typical and atypical conditions, the acoustic waveforms
were checked following Paulmann, Pell, and Kotz (2008). As shown in Table 2, no signiﬁcant diﬀerences were found between typical/
atypical conditions in terms of duration, highest and lowest pitch, or intensity of -ne and -yo (all p's ns.). Additionally, the lengths ofthe entire target turns, including the SFPs in the target dialogs, were not signiﬁcantly diﬀerent between typical (M = 2036 ms,
SD = 218) and atypical usages (M = 1932 ms, SD = 272; t78 = 1.851, p = .068, d = .051). The sound ﬁles for an example stimulus
dialog set can be found at http://skiyama.com/research.
2.1.3. Procedure
The participants completed an appropriateness judgment task while their EEGs were recorded in a sound-attenuated room. They
were seated in front of a monitor and were shown a ﬁxation mark (+) in the center of the monitor for 2000 ms before they heard thestimulus dialog through a set of loudspeakers. We then presented another ﬁxation (+) for 3000 ms, after which the participants wereasked to indicate via button press whether the use of the SFP(s) at the end of each dialog was appropriate or not as soon as the
instruction appeared in the monitor (Fig. 2). We inserted a long inter-stimulus interval (ISI) before asking for the judgment to prevent
possible muscle activity caused by the button press. Before the experiment proper started, the participants were given 16 practice
trials to get familiarized with the task. The volume was adjusted if needed. The participants were asked to minimize eye blinking
while listening to the dialogs. The experiment consisted of 4 blocks, with a small break between each block. At the beginning of eachblock, which contained 58 proper trials and took about 10 min, 3 warm-up trials were included. The stimulus dialogs were presented
in random order during the blocks. Each participant listened to both typical and atypical usages of the same dialog, but one of the two
usages was always given within the ﬁrst two blocks, while the other was contained in the second two blocks, in order to minimize apotential repetition eﬀect. Within both the ﬁrst and the second two blocks, items were presented in random order. On average, theprocedure took approximately 50 min for the task itself, without preparation for EEG recording. The presentation of stimuli and theobtaining of behavioral data were conducted with E-Prime 2.0 (Psychology Software Tools, Pittsburgh, PA).
2.1.4. Electrophysiological data acquisition and processing
The EEG signal was continuously recorded at a sampling rate of 512 Hz from 32 active Ag-Cl electrodes at standard positions of
the international 10-20 system using a BioSemi ActiveTwo ampliﬁer system (BioSemi B.V., Amsterdam, the Netherlands). The signal
was referenced oﬄine by tin electrodes attached to the left and right mastoids. Eye blinks were measured with tin electrodes placed
one above and another underneath the left eye. Horizontal eye movements were measured with two electrodes, one on the external
canthus of each eye. Automatic rejections on a participant-by-participant basis were performed to discard artifacts from blinks,
movements, or technical malfunctions (amounting to the exclusion of 8.35% of the trials). The EEG data were corrected for eye-blink
artifacts using the Gratton, Coles, and Donchin (1983) algorithm. For non-ocular artifacts, we removed trials with amplitudes below−200 μV and above +200 μV. Furthermore, trials that produced a 100 μV or greater voltage step within 200 ms were removed fromthe analysis. Filters (high-pass: 0.01 Hz/24 dB and low-pass: 40 Hz/24 dB) were applied for the data analyses, and a baseline
correction was applied with a pre-response interval from −200 to 0 ms. Epochs of 800 ms were computed with a 200 ms pre-stimulus
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Fig. 1. Example of sound wave of a stimulus turn ending with Japanese SFPs -ne and -yo.
Notes: The blue contour and the green contour represent pitch and intensity, respectively. The abbreviations represent the following: COP [Copula], NOM [Nominative
case marker], PST [Past].

baseline. ERP onset was triggered at the beginning of the SFP presentation (Fig. 1). We used E-Prime 2.0 to write marker data onto thecontinuous EEG signal as well as for stimulus presentation.
2.1.5. Statistical analysis
The purpose of this study was to detect individual diﬀerences in mentalizing ability among the general population, and not tomake a group comparison of autistic people (i.e., extremely low-ability mentalizers) versus healthy controls. To examine the eﬀect ofeach individual's mentalizing ability on ERP components and the sensitivity to Japanese SFPs as linguistic markers of interpersonal
distance, we performed a linear mixed eﬀects (LME) modeling (e.g., Baayen, 2008) based on the maximum-likelihood method. Thiswas done instead of grand-averaging ERP components by dividing participant groups into high- and low-ability mentalizers. The LME
method estimates the eﬀects of ﬁxed variables (both continuous and categorical, or within- and between-participant variables together) that are of interest in the study over random eﬀects that can be assumed to be randomly sampled from the population (e.g.,
Baayen, Davidson, & Bates, 2008; Davidson & Indefrey, 2007; Locker, Hoﬀman, & Bovaird, 2007; Moratti, Clementz, Gao, Oritz, &Keil, 2007). We used this technique for the ERP data as well as for behavioral data analysis. The application of LME modeling to ERP
data analysis has been validated by several recent neurolinguistic studies (e.g., Newman, Tremblay, Nichols, Neville, & Ullman, 2012;
Wang, Verdonschot, & Yang, 2016) that examined how individual diﬀerences such as foreign language ability scores (i.e., continuous
variables) and other categorical independent variables interact to inﬂuence ERP components. The model estimation was conductedusing the lme4 (Bates, Mächler, Bolker, & Walker, 2014a) and lmerTest (Kuznetsova, Brockhoﬀ, & Christensen, 2014) packages
implemented in R version 3.0.2. The alpha level was set at .05 for all statistical tests in this study. All continuous variables werescaled before analysis to obtain standardized ﬁxed-eﬀect parameters.
To analyze the behavioral data in terms of accuracy rate (AR: the ratio of expected responses to the number of trials in eachcondition) and reaction time (RT), participants' AQ Scores, SFP (i.e., -ne and -yo), and Typicality (i.e., Typical and Atypical usages ofeach SFP) were set as ﬁxed factors in the modeling, combined with Stimulus Dialog and Participant as random variables. The RT data
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Table 2
Acoustic characteristics of the stimulus target turns including Japanese SFPs -ne and -yo.
-neDuration (ms)Highest pitch (Hz)Lowest pitch (Hz)Intensity (dB)

TypicalAtypicalM (SD)

M (SD)

285 (49)228 (20)184 (26)
67 (2)

297 (45)226 (20)190 (29)
67 (3)

-yo
t

p

1.664
−.299
1.040
−.378

ns.
ns.
ns.
ns.

TypicalAtypicalM (SD)

M (SD)

298 (46)
195 (21)128 (33)
63 (4)

285 (49)
195 (17)131 (37)
65 (4)

tp−1.288
−.037
.346
1.334

ns.
ns.
ns.
ns.

was trimmed at 2.5 SDs above the mean of each condition for each participant, and responses outside of 2.5 SDs at both high and low
ranges were replaced by boundaries indicated by 2.5 SDs from the individual means of participants in each condition (2.8% of thedata were changed). The model used in the behavioral data analysis was [AR/RT ∼ Typicality * SFP *AQ + (1|Dialog) + (1|Participant)], which is a standard formula for LME (using the lme4 package), in which the dependent variable
presented before the tilde sign (∼) is described by a statistical model speciﬁed using ﬁxed eﬀects (variables without parentheses) andrandom eﬀects (variables between parentheses, expressed as 1| < factor >). A plus (+) indicates an addition to the model, and an
asterisk (*) indicates an interaction as well as each main eﬀect (see Bates, Mächler, Bolker, & Walker, 2014b for a comprehensive
overview). Using this formula, either AR with the function glmer() or RT with the function lmer() was predicted by the three ﬁxed
factors of SFP, Typicality (categorical, within-participant variables), and AQ (continuous, between-participant variable), their interaction eﬀects (denoted by asterisks), as well as two random factors for each item (i.e., stimulus dialog) and each participant.
For ERP data analysis, we used the model [ERP ∼ Typicality * ROI * SFP * AQ + (1|Participant) + (1|Electrode)], in which theobtained ERP was predicted by the ﬁxed factors of Typicality, Region of Interest (ROI; i.e., anterior, central, and posterior regions of
the brain), SFP, AQ Score, the interaction terms of these four factors, as well as Participant and Electrode as random factors. We
extracted ERP data for each condition of typical/atypical usage of -ne and -yo during the time window of 150–400 ms (following Fajaet al., 2016, who examined this EPN component in relation to emotion recognition and perceptual attention in autism). To set up the
ROI, we assigned channels FP1/2, AF3/4, Fz, F3/4, F7/8 for the anterior region, Cz, C3/4, T7/8, CP1/2, and CP5/6 for the central
region, and Pz, P3/4, P7/8, PO3/4, Oz, and O1/2 for the posterior region.

Fig. 2. Experimental trial for SFP appropriateness judgement task in Experiment 1.
Note: Everything was presented in Japanese for the actual experiment.

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2.2. Results
2.2.1. Behavioral data
Generally, participants judged the typical usage of the SFP -ne to be appropriate in almost all the stimulus dialogs (M = .960,
SD = .195 for -ne; M = .973, SD = .032 for -yo), while they tended to judge the atypical usage as inappropriate (M = .774, SD = .418
for -ne; M = .744, SD = .208 for -yo). The LME analysis indicated that the AR of the responses was signiﬁcantly higher for typicalusage than for atypical usage (β = 2.615, z = 7.298, p < .001). The main eﬀects of the other independent variables, SFP(β = −.193, z = −.685, p = .494) and AQ (β = −.256, z = −1.124, p = .261), as well as any of their interaction eﬀects, were notsigniﬁcant. The mean RT for the projected answers of this task was faster for typical usage (M = 361 ms, SD = 191 for -ne;
M = 404 ms, SD = 179 for -yo) than for atypical usage (M = 500 ms, SD = 189 for -ne; M = 520 ms, SD = 202 for -yo; β = −.368,
t = −7.414, p < .001). No signiﬁcant inﬂuences of SFP (β = .065, t = 1.242, p = .216) and AQ (β = −.027, t = −.237, p = .814)
or the interaction eﬀects between the variables were found in the RT data. Note that it is diﬃcult to derive strong conclusions fromthe RT data in any case given the large 3000 ms ISI.
2.2.2. Electrophysiological data
Preliminary visual inspection of the ERP waveforms on the grand average of all participants in response to the presentation of
SFPs -ne and -yo (Figs. 3 and 4, respectively) suggested greater early negativity in the central and posterior regions (i.e., early
posterior negativity: EPN) for the atypical than for the typical usage of SFPs. We then continued to examine, over the typical EPN time
window of 150–400 ms (Faja et al., 2016) and utilizing LME, how individual mentalizing abilities aﬀected the amplitude and scalp
distribution. Table 3 summarizes the ﬁxed eﬀects of SFP, ROI, Typicality, AQ, and the two-way, three-way, and four-way interactions
among these factors on ERP amplitudes. In all, we observed a signiﬁcant interaction between Typicality (typical vs. atypical usage)and ROI (anterior vs. posterior regions; β = −.320, t = −3.241, p = .001), generally indicating a greater negativity between 150
and 400 ms in the posterior region in comparison with the anterior region for atypical SFP usage (both with -ne and -yo) than for
typical usage. This eﬀect is greater for -ne than for -yo based on the three-way interaction (β = .292, t = 2.095, p = .036). Further, asigniﬁcant four-way interaction between Typicality, ROI (anterior vs. posterior), SFP, and AQ revealed that participants with higher
AQ scores (i.e., lower mentalizing ability) expressed a greater negativity in the posterior region compared with the anterior region in
response to atypical SFP usage than its typical counterpart, especially with -ne as opposed to -yo. The inter-individual diﬀerences interms of AQ score on the ERP eﬀects for atypical SFP usage are shown in Fig. 5.
2.3. Discussion
Native Japanese speakers in general seem to display some uncertainty when understanding atypical usages of the SFPs -ne and -yo,
as they took a longer time to make appropriate judgments for atypical than for typical usages. This tendency may relate to somesalient feature of sentence processing in Japanese as a pro-drop language. That is, the stimulus dialogs created for this study lacked
the subject when it was a pronoun, as this is common and natural in spoken Japanese (e.g., Iwasaki, 1993; Sakamoto, 2002). Utilizing
diversiﬁed usages of Japanese sentences with and without SFPs, Tamaoka, Matsuoka, and Sakamoto (2007) demonstrated that SFPs
generally interfere with identiﬁcation of the referent of subject-lacking sentences compared with subject-including sentences. It could
thus be surmised that the observed response delay in SFP understanding may especially originate from atypical SFP usage rather thantypical usage based on the present behavioral data, even though the delay could be obscured by the long ISI (i.e., 3000 ms) before thejudgment.
The electrophysiological ﬁndings of Experiment 1 represent the neural activity expressed when native Japanese speakers paid
explicit attention to whether the presented SFPs -ne and -yo were appropriate in a given dialog. We observed a greater EPN for theatypical usage in comparison with the typical usage in participants with higher AQ scores (i.e., lower mentalization ability) than inthose with lower scores, and this eﬀect was greater for -ne than for -yo. The result suggests that low-ability mentalizers have astronger sense of strangeness toward atypical usage of the SFP -ne. One plausible reason for this could be that, as the SFP -ne
encompasses a complicated and diverse range of usages depending on the context and interpersonal relationships, the addressee of-ne is required to ﬂexibly interpret the addresser's attitude in a given situation. The greater EPN in low-ability mentalizers, who are
impaired when it comes to forming the meta-representation of attributing others' beliefs to their behavior, and are hence are nottolerant enough to the dynamic and often chaotic changes in social interactions (Baron-Cohen, 1995), might reﬂect a more irregular
ERP pattern in response to atypical usage of the SFP -ne.
However, we should hesitate to immediately conclude that the ﬁndings represent a full and accurate reﬂection of neural activity
in actual person-to-person encounters. In real encounters, most Japanese speakers would not pay speciﬁc attention to SFP usage andto judging its appropriateness, but rather involuntarily perceive the addresser's attitude toward interpersonal relationships throughSFP usage in the discourse. This being the case, we conducted another experiment to replicate the ﬁndings from Experiment 1,
making use of a content comprehension task. In this experiment, participants were not required to make any judgment concerning
SFPs. Instead, they simply had to comprehend what information was exchanged in the given stimulus dialogs. We believe this task ismore similar to an actual person-to-person encounter.

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Fig. 3. Grand averaged ERPs time-locked to the onset of Japanese SFP -ne during the appropriateness judgment task. EPN: early posterior negativity.

Fig. 4. Grand averaged ERPs time-locked to the onset of Japanese SFP -yo during the appropriateness judgment task. EPN: early posterior negativity.

3. Experiment 2: understanding SFPs during a content comprehension task
In Experiment 2, we administered a content comprehension task to investigate whether similar ERP patterns could be observed
when native speakers listened to SFPs without explicit instruction concerning SFPs.

3.1. Materials and methods
3.1.1. Participants
Twenty-two healthy right-handed graduate and undergraduate students (8 males; age range: 19-30, M = 21.2, SD = 2.5) who
participated in neither Experiment 1 nor the pilot manipulation check participated in this experiment. They were administered theJapanese version of the AQ test (Wakabayashi et al., 2006) and scored from 11 to 36 (M = 22.5, SD = 6.4). They gave informed
consent and received ﬁnancial compensation for participation.

3.1.2. Materials
The stimulus dialogs that included the SFPs (both target and ﬁller) were identical to those in Experiment 1.
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Table 3Fixed eﬀects of LME analysis on ERP amplitude in the 150–400 ms time window during the appropriateness judgment task of Japanese SFP -ne.
Contrast(intercept)
Typical vs. Atypical
Anterior vs. Central
Anterior vs. Posterior-ne vs. -yo
AQ
Typ/Atyp vs. Ant/Cent
Typ/Atyp vs. Ant/Post
Typ/Atyp vs. -ne/-yo
Ant/Cent vs. -ne/yo
Ant/Post vs. -ne/-yo
Typ/Atyp vs. AQ
Ant/Cent vs. AQ
Ant/Post vs. AQ-ne/-yo vs. AQ
Typ/Atyp vs. Ant/Cent vs. -ne/-yo
Typ/Atyp vs. Ant/Post vs. -ne/-yo
Typ/Atyp vs. Ant/Cent vs. AQ
Typ/Atyp vs. Ant/Post vs. AQ
Typ/Atyp vs. -ne/-yo vs. AQ
Ant/Cent vs. -ne/-yo vs. AQ
Ant/Post vs. -ne/-yo vs. AQ
Typ/Atyp vs. Ant/Cent vs. -ne/-yo vs. AQ
Typ/Atyp vs. Ant/Post vs. -ne/-yo vs. AQ

Estimate: βtp−.387 [−.628, −-.146]−.046 [−.174, .081].529 [.326, .731]
1.077 [.881, 1.273].266 [.138, .393]−.136 [−.360, .088]−.177 [−.377, .022]−.320 [−.513, −-.126]−.425 [−.605, −-.244]−.085 [−.285, .114]−.298 [−.492, −-.105].146 [.018, .274].179 [.038, .321].253 [.116, .390].300 [.172, .427].130 [−.152, .412].292 [.019, .566]−.198 [−.397, .002]−.330 [−.524, −-.137]−.319 [−.499, −-.138]−.008 [−.207, .192]−.175 [−.369, .018]−.028 [−.311, .254].275 [.001, .548]−3.235−.711
5.191
10.9044.083−1.229−1.741−3.241−4.616−.838−3.023
2.244
2.493
3.620
4.601
.901
2.095
−1.944−3.347−3.465−.075−1.775
−.197
1.968

.002
.477
< .001< .001< .001
.229
.082
.001
< .001
.402
.003
.025
.013
< .001< .001
.368
.036
.052
.001
.001
.940
.076
.844
.049

Note. Values in brackets denote 95% conﬁdence intervals. AQ: Autism-Spectrum Quotient.

Fig. 5. Partial regression plot between the scaled Autism-Spectrum Quotient (AQ) score and the scaled residuals from ERP amplitude for atypical minus typicalJapanese SFPs of the posterior minus anterior region within the 150–400 ms time window during the appropriate judgement task (n = 21).

3.1.3. Procedure
The procedure was identical to that in Experiment 1, except that participants underwent a “content comprehension task” toconﬁrm that they had properly listened to the information that was exchanged during the stimulus dialogs. In Experiment 2, theparticipants were required to listen to the stimulus dialogs and then answer a simple comprehension question by pressing the true or
false button when a description about the dialog content was presented. For example, when the statement “It seems the woman likes
the spa” appeared on the computer screen, the participants were supposed to press the “false” button for the correct answer because
the stimulus dialog indicated that it was the man, and not the woman, who went to the spa, and the female speaker in the second turnresponded with “(You) really like the spa.” As it was necessary that the content comprehension concerned factual things about which
to make an explicit true-false judgment, the items for the addressee-oriented conditions (i.e., typical -ne and atypical -yo) asked about
the male speaker (whose action was described in the ﬁrst turn), and those for the addresser-oriented conditions (i.e., typical -yo and9Journal of Neurolinguistics 47 (2018) 1–15

S. Kiyama et al.

atypical -ne) asked about the female speaker (whose action was stated in the second turn). We prepared questions whose correct
answer was “true” for half of the dialogs and “false” for the other half. In Experiment 2, no mention was made to the participants
concerning SFPs until they were debriefed.
3.1.4. Electrophysiological data acquisition and processing, and statistical analyses
Identical to Experiment 1, 2.7% of the RT data were changed due to the same trimming procedure in Experiment 1.
3.2. Results
3.2.1. Behavioral data
The participants overall showed a high accuracy rate in the content comprehension task including the ﬁller stimuli (M = .945,
SD = .018). Particularly for the target stimuli including -ne and -yo, the AR data was generally high for both typical (M = .975,
SD = .026 for -ne; M = .943, SD = .033 for -yo) and atypical (M = .960, SD = .030 for -ne; M = .869, SD = .043 for -yo) usages.
None of the independent variables of Typicality (β = .545, z = 1.822, p = .068), SFP (β = −.471, z = −.896, p = .370), or AQ(β = .241, z = 1.245, p = .213) reached signiﬁcance. RTs for the correctly-answered items were faster for typical usage(M = 1460 ms, SD = 508 for -ne; M = 1410 ms, SD = 420 for -yo) than for atypical usage (M = 1541 ms, SD = 497 for -ne;
M = 1460 ms, SD = 427 for -yo). The main eﬀects of Typicality (β = −.096, t = −2.411, p = .016), SFP (β = −.166, t = −2.566,
p = .011), and their interaction eﬀect (β = .189, t = 3.031, p = .002) were signiﬁcant, indicating that participants took a longer time
to comprehend dialogs with atypical SFP usages than typical ones, and this eﬀect was greater for -ne than for -yo. The eﬀect of AQ(β = −.044, t = −1.252, p = .211) was not signiﬁcant. As in Experiment 1, we should be cautious with strongly interpreting RT
ﬁndings due to the large interval (3000 ms) before the decision was made.
3.2.2. Electrophysiological data
Based on a preliminary visual inspection of ERP waveforms during -ne on the average of all the participants (Fig. 6), we set thesame time window (during 150–400 ms) to conduct an LME analysis comparable to that in Experiment 1 (following Faja et al., 2016),
even though the two conditions (i.e., typical vs. atypical) for -yo showed almost the same pattern (Fig. 7). The results of this LME
modeling (Table 4) revealed a tendency similar to that in Experiment 1. While atypical SFP usage generally elicited a greater
negativity than typical usage in the central (β = .239, t = 2.204, p = .028) and posterior regions (β = .481, t = 4.577, p < .001)
than in the anterior region, this negativity was much greater for atypical -ne usage than the -yo counterpart both in the central(β = −.383, t = −2.500, p = .012) and posterior (β = -.720, t = −4.848, p < .001) regions. Again, participants with a higher AQ
score (i.e., low-ability mentalizers) expressed a greater negativity in the posterior region in comparison with the anterior region for
atypical usage of -ne than that of -yo, both of which were also greater than for their typical usage. The inter-individual diﬀerences interms of AQ on the ERP eﬀect while understanding the SFPs -ne and -yo are shown in Fig. 8.
3.3. Discussion
As the participants showed high accuracy overall in the content comprehension task for both the target and ﬁller stimuli, we
conﬁrmed that they paid proper attention to the auditorily presented dialogs with SFPs. Interestingly, this task elicited a uniquenessof -ne understanding in comparison with that of -yo, such that participants took longer to comprehend dialog content with atypicalusages of -ne than with either atypical usages of -yo or the typical usages of both -ne and -yo. What might have interfered with theirsmooth comprehension of turns with an atypical -ne could perhaps be associated with their involuntary consideration of the diverse
possibilities of -ne usage, as discussed in Experiment 1. Native speakers may try to connect a variety of imaginable situations with thedialogs ending with -ne, even when these are not yet in the picture.
The uniqueness of understanding atypical -ne usages was also found in ERP data in Experiment 2, where the dialog contents werecomprehended without explicit instruction about SFPs themselves, unlike in Experiment 1. Native Japanese speakers with a lower
mentalizing ability expressed a greater EPN in response to the atypical usage of -ne than the typical usage, although they did notexhibit this for -yo understanding. This suggests that those with lower mentalizing abilities may be hypersensitive to the atypical -ne
as a linguistic marker of interpersonal distance, even when they are not required to judge the appropriateness of the marker itself.
4. General discussion
The present study shed light on inter-individual diﬀerences in mentalizing ability when understanding Japanese linguistic indicators of interpersonal distance. In this study, we employed two listening modes within the ERP experiments. One mode required an
appropriateness judgment of the SFPs, while the other contained no explicit instruction regarding the SFPs. The results consistently
revealed that the earlier ERP component (i.e., the EPN) was larger when native Japanese speakers heard an atypical usage of the SFP-ne, as compared to its more typical usage, while both usages were grammatical. Additionally, the EPN eﬀect was found to besigniﬁcantly greater in participants with a lower mentalizing ability.
Concerning the neurophysiological underpinnings of this phenomenon, previous ERP ﬁndings (e.g., Hirotani & Schumacher,2011; Liu et al., 2009; Nieuwland et al., 2010) have led us to speculate whether a “pragmatic N400 eﬀect” might arise during theunderstanding of Japanese SFPs as their appropriateness cannot be judged without social context. Instead, we expected an EPN eﬀect,
which has been shown to reﬂect emotional processing (Faja et al., 2016), as the Japanese SFP -ne often conveys empathy between the10

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Fig. 6. Grand averaged ERPs time-locked to the onset of Japanese SFP -ne during the content comprehension task without explicit instruction on SFPs. EPN: early
posterior negativity.

addresser and the addressee (e.g., Cook, 1990, 1992; Maynard, 1997). Our two experiments found a consistent earlier negativity
between 150 and 400 ms in the posterior region (i.e., EPN) especially after the presentation of atypical -ne as opposed to typical -ne.
The short duration of the marker (i.e., each SFP consists of only a single moraic symbol) might have resulted in an earlier negativedeﬂection. This ﬁnding is in line with Kissler and Herbert (2013), who found EPN in response to emotional words in a reading
paradigm, interpreting it as a reﬂection of spontaneous attentional highlighting of motivationally relevant emotional stimuli. Although the eﬀect of quicker access to emotional stimuli has previously been reported only in reading designs, the present study now
contributes evidence of the eﬀect in the auditory realm of word processing.
Mittermeier et al. (2011) also found the EPN component within the auditory modality by utilizing an emotional choice reaction
paradigm where the participants judged whether the auditorily presented emotional syllables/words had positively emotional, negatively emotional, or neutral intonation. They observed a greater EPN for the emotional stimuli with both positive and negative
intonation, compared with neutral intonation. We, contrarily, did not obtain a similar outcome as revealed by an intonation analysis
of our auditory stimuli, but manipulated the typicality of the usage of Japanese SFPs. As a result, we found a greater EPN eﬀect
especially during the understanding of atypical -ne as opposed to typical -ne. This eﬀect, however, was not found in typical/atypicalusages of -yo. This ﬁnding supports the view that the SFP -ne itself arouses emotion, even without noticeable intonation.
Further, we found an enhanced EPN eﬀect for atypical SFP -ne than typical -ne particularly in participants with lower mentalizing
ability as opposed to those with higher mentalizing ability. This ﬁnding might reﬂect a hypersensitivity associated with individual

Fig. 7. Grand averaged ERPs time-locked to the onset of Japanese SFP -yo during the content comprehension task without explicit instruction on SFPs.

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Table 4
Fixed eﬀects of LME analysis on ERP amplitude in the 150–400 ms time window during the understanding of the Japanese SFP -ne within the content comprehension
task without explicit instruction on SFPs.
Contrast(intercept)
Typical vs. Atypical
Anterior vs. Central
Anterior vs. Posterior-ne vs. -yo
AQ
Typ/Atyp vs. Ant/Cent
Typ/Atyp vs. Ant/Post
Typ/Atyp vs. -ne/-yo
Ant/Cent vs. -ne/yo
Ant/Post vs. -ne/-yo
Typ/Atyp vs. AQ
Ant/Cent vs. AQ
Ant/Post vs. AQ-ne/-yo vs. AQ
Typ/Atyp vs. Ant/Cent vs. -ne/-yo
Typ/Atyp vs. Ant/Post vs. -ne/-yo
Typ/Atyp vs. Ant/Cent vs. AQ
Typ/Atyp vs. Ant/Post vs. AQ
Typ/Atyp vs. -ne/-yo vs. AQ
Ant/Cent vs. -ne/-yo vs. AQ
Ant/Post vs. -ne/-yo vs. AQ
Typ/Atyp vs. Ant/Cent vs. -ne/-yo vs. AQ
Typ/Atyp vs. Ant/Post vs. -ne/-yo vs. AQ

Estimate: βtp-.118 [-.337, .102]-.203 [-.339, −-.067].109 [-.041, .259].256 [.110, .401]-.138 [-.273, −-.002]-.436 [-.655, −-.217].239 [.026, .451].481 [.275, .687].252 [.06, .444].299 [.087, .511].300 [.094, .506].343 [.207, .479].067 [-.084, .217].134 [-.012, .279].199 [.063, .334]-.383 [-.683, −-.083]-.720 [-1.012, −-.429]-.126 [-.338, .087]-.340 [-.546, −-.134]-.300 [-.492, −-.108]-.048 [-.261, .164].060 [-.146, .266].209 [-.091, .510].330 [.039, .621]−1.084−2.9331.419
3.439−1.985−4.018
2.204
4.577
2.573
2.761
2.855
4.954
.869
1.799
2.866
−2.500−4.848−1.162−3.240−3.064
-.445
.573
1.365
2.220

.286
.003
.156
.001
.047
< .001.028< .001
.010
.006
.004
< .001
.385
.072
.004
.012
< .001
.245
.001
.002
.657
.567
.172
.027

Note. Values in brackets denote 95% conﬁdence intervals. AQ: Autism-Spectrum Quotient.

Fig. 8. Partial regression plot between the scaled Autism-Spectrum Quotient (AQ) score and the scaled residuals from ERP amplitude for atypical minus typicalJapanese SFPs of the posterior minus anterior region within the 150–400 ms time window during the content comprehension task without explicit instruction on SFPs
(n = 22).

mentalizing ability. As people with insuﬃcient mentalizing ability are known to portray low mental ﬂexibility in social interactions(e.g., van Eylen et al., 2011), it is not inconceivable that they are comparatively unable to grasp subtle indications of interpersonal
relationships revealed by linguistic markers in actual encounters. This may result in a stereotypical interpretation of SFP -ne usage,
which causes inappropriate detection of an atypical -ne. In a similar vein, high-ability mentalizers may be tolerant of atypical -ne
because they are ﬂexible enough and try to ascertain others' attitudes attached to potential usage(s) of -ne. Even with suﬃcient
linguistic knowledge of grammar and vocabulary, some native speakers seem to have a certain degree of diﬃculty recognizing social
distance in language communication, so they experience a sense of uneasiness toward interpersonal relationships. Lack of tolerance toatypical SFP usage might partially contribute to this.
We should note that the increased EPN eﬀect for low-ability mentalizers has been shown especially for understanding atypical -ne
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than typical -ne, but the eﬀect was not found in -yo. This result likely stems from the basic feature of -ne as an addressee-oriented
particle in its typical usage. Unlike the addresser-oriented -yo, -ne inevitably claims the addressee's attention because it indicates thatthe stated proposition relates to the addressee(s), and not the addresser (Takiura, 2008). This feature of addressee orientation may
underlie the diversity of -ne usages and the individual diﬀerences in native speakers' neural reactivity to it, as shown in our ERP
results. This characteristic of -ne is shown to have an eﬀect even on bystanders, as the current study had the participants as bystanders(not as addressees) of the stimulus dialogs. As suggested in Tamaoka et al. (2007), even a bystander must use their mentalizing ability
to infer what the addressee interprets from the addresser's utterance. Our ERP experiments do suggest that the Japanese SFP -ne
fulﬁlls a diversiﬁed role that enables native Japanese speakers to readily understand a discourse (despite the lack of pronouns).
Naturally, the current study has some limitations. First, we did not manipulate prosody in our auditory stimulus dialogs with SFPs
in order not to induce any confounding pragmatic implications. However, some prosodic manipulations of SFPs (i.e., to arouseemotions) could elicit larger neural reactivity, as Paulmann, Pell, and Kotz (2008) and Kissler and Herbert (2013) have demonstrated.
The present study, as the ﬁrst attempt at neurophysiological observation of Japanese SFPs, employed the simple dichotomy ofaddresser-/addressee-oriented content in the given sentences. Nevertheless, with respect to discourse comprehension, more elaboratemechanisms of involuntary attention to SFPs might be hidden in subtle prosodic changes, which could only be perceived by highability mentalizers. Second, even though our two experiments consistently support individual diﬀerences in linguistic pragmatic
comprehension by native Japanese speakers, further replication studies are necessary to better understand the eﬀect of mentalizing
ability on the understanding of Japanese SFPs, as the number of participants in the present experiments might have been relatively
small. Although we currently refer to the ERP eﬀect obtained from our experiments as EPN, subsequent studies are necessary to
conﬁrm the ERP label (as the present study was the ﬁrst to examine Japanese SFPs in auditorily presented dialogs).
Additionally, as the present study only examined simple bound morphemes (i.e., the SFPs -ne and -yo), we should be cautious togeneralize that the emotional EPN component reﬂects sensitivity to any linguistic markers that indicate interpersonal distance inother languages. Given the abundance of discourse functions of SFPs as bound morphemes at the right periphery (Yap, Yang, & Wong,2014, pp. 179–220), it might be a typologically common motivation throughout particular East and South-East Asian pro-drop
languages that SFPs might have evolved for eﬃcient modulation of interpersonal distance in chaotic communication, reliant on
individuals' sensitive awareness of others' mental states. Although we only examined Japanese, cross-linguistic insights into theneural mechanisms for the understanding of SFPs in relation to the pro-drop phenomenon will prove to be informative.
5. Conclusion
Our study presents the ﬁrst electrophysiological evidence that a linguistic marker (i.e., the Japanese SFP -ne) serves as an indicator of interpersonal relationships that can prompt emotions in the addressee, and that the degree of an individual's mentalizing
ability regulates their ﬂexibility in recognizing others' attitudes via the various usages of the marker. Low-ability mentalizers seem toadopt a more stereotypical understanding of the SFP, which might underlie their diﬃculty with ﬂexibly recognizing interpersonal
distances in social encounters.
Conﬂicts of interest
The authors declare that they have no conﬂicts of interest.
Acknowledgements
The authors are grateful to Kalinka Timmer, Masato Takiura, Shingo Tokimoto, Kuniya Nasukawa, and Masatoshi Koizumi, as
well as the two anonymous reviewers, for their invaluable comments on earlier versions of this manuscript. They also thank Nobuhiro
Saito for stimulus recording. This study was funded by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid program(24652080 and 16H05940 awarded to SK; 17K02748 awarded to RV; and 16K13242 awarded to KT).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jneuroling.2018.01.005.
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