ERP correlates of compositionality in Chinese idiom comprehension

Journal of Neurolinguistics 26 (2013) 89–112

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ERP correlates of compositionality in Chinese idiom comprehension Hui Zhang a, *, Yiming Yang b, **, Jiexin Gu b, Feng Ji a a b

Research Centre for Linguistics and Applied Linguistics, Nanjing International Studies University, Nanjing 210039, China Jiangsu Key Laboratory of Linguistic Science and Neuro-cognition, Jiangsu Normal University, Xuzhou 221009, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 November 2011 Received in revised form 14 May 2012 Accepted 17 May 2012

Based on compositionality, this paper proposes a three-grade hierarchy to classify 108 Chinese idioms (comparatively familiar and literally plausible) into three groups. With 36 non-idiomatic literal phrases as the control group, the present study used the event-related (brain) potentials (ERPs) to investigate the time course of Chinese idiom comprehension and the effects of compositionality on this process. Primed by their literal interpretations, Chinese idioms with varying degrees of compositionality and non-idiomatic phrases were visually presented to subjects for performing a semantic judgment task. The results showed a graded modulation of two ERP components (i.e., the N250 and the N400): for the Chinese idioms, stimuli with high compositionality elicited the smallest ERP effects, while stimuli with low compositionality the largest; compared with idioms, literal non-idioms induced larger amplitudes with regard to both the components. The N250 has been reported for the first time in ERP studies of the Chinese language. In view of unique features of Chinese characters, the functional significance of the two components provides converging evidence for distinct effects of compositionality on activating figurative meanings in processing Chinese idioms, and that language users attempted to do some compositional analysis in this process. Moreover, putative cognitive processes reflected by the two components contribute to an interim model specified for processing Chinese idioms: prelexical form recognition coinciding with early meaning retrieval, followed by postlexical semantic integration with contextual constraints. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: ERP Chinese idiom Compositionality Semantic priming N250 N400

* Corresponding author. Tel.: þ86 25 52429891; fax: þ86 25 80838421. ** Corresponding author. Tel./fax: þ86 516 83403513. E-mail addresses: [email protected] (H. Zhang), [email protected] (Y. Yang). 0911-6044/$ – see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jneuroling.2012.05.002

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1. Introduction In Chinese lexical system, Chinese idioms are a typical unit. As an individual type in the domain of idioms, most Chinese idioms have some unique qualities. One of the design features of most Chinese idioms on the dimension of form characteristics is the four-character formdthe Chinese lexicon provides an exact number of the characters in such a unit. According to the statistics given in Zhou (2004, p. 230), up to 95.57% entries in Dictionary of Chinese Idioms (1987) are four characters. The uniformity in form regulates to a large extent some other linguistic characteristics of Chinese idioms, specifically phonological and semantic distribution. Compatible with the rhythmical arrangement and prosodic features represented by the two-plus-two syllables,1 a great number of Chinese idioms consist of double substructures, mostly parallel with each other (Sun, 1989, p. 77). Branded with a distinct national style, Chinese idioms mirror the esthetic pursuit of symmetry deeply embedded in oriental thinking. Concise in surface form, the multidimensional nature of Chinese idiom semantics is yet a tough nut to crack. The meanings of idioms “typically involve a conflation of social, political, contextual, attitudinal, and emotional factors” (Van Lancker Sidtis, 2006, p. 215). Through long years of interactions with a variety of factors, abstruse meanings have been gradually and deeply condensed into the stereotyped forms of Chinese idioms. Sharing this opinion, Langlotz (2006, p. 3) made a claim that “idioms are linguistic constructions that have gone through a sociolinguistic process of conventionalisation”. Chinese idioms do not have their core meanings established in a short period. It is the force of convention that often makes the already established idiomatic meanings unavailable to language learners who understand language merely by grammatical rules. In discussing the relationship between the two meaning levels of Chinese idioms, Ma (1985, p. 239) set forth a classical statement: Chinese idioms live by the figurative meanings that live by the literal meanings of themselves. Liu (1990) stated that the most important feature of the majority of Chinese idioms is their double planes of meanings: people must see through the literal meaning to get what a Chinese idiom really means. Chinese idioms set a consummate example in the large family of idioms across the world, not only in their unique external form, but more importantly, in their protean internal semantic relations. Traditional approaches regarded idioms as noncompositional word strings without any compositional characteristics at the level of semantics; the idiomatic meanings of idioms are in no way derived from meanings of their constituent words. In this view, an idiom is modeled as a chunk in the mental lexicon with a prepackaged and highly conventionalized meaning, rather than “a compositional function of the meanings of the idiom’s elementary parts” (Katz & Postal; as cited in Langlotz, 2006, p. 4). As one of the primary features to define idioms, “noncompositionality” has fully discounted the possibility of cognitively unfolding the semantic complexity of idioms in actual processing. With the advancement of linguistic theories and research methods, much work was done to anatomize semantic characteristics and internal semantic structure of idioms. Linguists adopt a challenging stance on the absolute irrelevance between meanings of constituent parts and meanings of idioms comprised of these parts. That is, idioms are not all noncompositional chunks, but exhibit intricate internal semantic structure according to different degrees of compositionality (Gibbs, 1994). Compositionality refers to the fact that the constituents of idioms “carry identifiable parts of their idiomatic meanings” (Nunberg, Sag, & Wasow, 1994, p. 496). That is, idiomatic meanings of some idioms can be systematically analyzed into parts that have distinct correspondence with meanings of their individual constituents. Semantic composition can be observed from both the bottom-up and top-down perspectives; the dimension of compositionality applies to the bottom-up perspective and describes direct literal contribution of a constituent to the idiomatic meaning of an idiom (Geeraerts, 1995, p. 61). Compositionality is in agreement with some compositional hypotheses which postulate the existence of certain metaphorical rather than arbitrary relations between meanings of an idiom’s components and the idiom’s overall idiomatic meaning (cf., Gibbs, 1992; Glucksberg, 2001; Zhang, 2003, p. 15). Literal word meanings of idioms can be variably mapped onto components of their idiomatic meanings. In our

1 In the Chinese language, each character is represented by one syllable. Therefore, most Chinese idioms are four-syllable combinations from the angle of phonological structure.

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study into the effects of compositionality in Chinese idiom online processing, we attach more significance to the corresponding relations between concepts designated by Chinese characters and elements profiled by idiomatic meanings than to global literal-figurative motivation. Revising the single semantic-chunk view of idiomaticity, phraseologists postulated various taxonomies to refine the semantic characterization of idioms. Despite some minor differences, they share a sorting criterion by appealing to internal semantics of idioms, or specifically, the contribution of literal meanings of constituent words in idioms to their overall meanings. Nunberg (1978) categorized English idioms into three categories: (a) nondecomposable idioms refer to phrases such as kick the bucket in which stipulated idiomatic meanings can hardly be derived in a compositional manner from constituent parts comprising the word sequence; (b) abnormally decomposable idioms are phrases such as spill the beans in which the referents of idioms’ constituent parts can be identified metaphorically (e.g., a metaphorical relation between spill and “divulge” in this idiom); (c) normally decomposable idioms are phrases such as pop the question in which some constituents of these idioms are used almost literally (e.g., question here refers to a specific question, i.e. a marriage proposal). In accordance with different qualities of the relationship between literal and idiomatic meanings of idioms, Cutler (1982) claimed that all idioms in English range between two types: one is with transparent patterns of semantic extension, such as grasp the nettle; the other is highly opaque in semantic relevance between these two levels, such as red herring. English idioms were classified into another three classes as opaque, transparent, and quasi-metaphorical (cf., Cacciari & Glucksberg, 1991; Glucksberg, 1993). Akin to nondecomposable idioms, opaque idioms refer to those phrases (e.g., kick the bucket) characterized by constraints on derivation of idiomatic meanings from their literal interpretations through compositional inference. Likewise, transparent idioms refer to phrases (e.g., spill the beans) similar to abnormally decomposable idioms, in which native speakers have intuition about a direct mapping from literal meanings of the component words to constituents of idiomatic meanings. Quasi-metaphorical idioms refer to phrases like carry coal to Newcastle in which the overall literal meanings metaphorically map onto their idiomatic meanings via allusions. To simplify previous classification of idioms, Nunberg et al. (1994) reiterated the existence of semantically compositional idioms and put forward a dichotomy between idiomatically combining expressions (or idiomatic combinations) and idiomatic phrases. The former refers to idioms whose idiomatic meanings can be distributed across their constituent parts, such as pull strings. The latter refer to idioms whose idiomatic meanings cannot be distributed across their constituent parts, such as kick the bucket. In this paper we try to demonstrate that the dimension of compositionality2 influences the processing of Chinese idioms and serves as a feasible criterion for classifying Chinese idioms. However, until now the empirical evidence supporting the psychological reality of compositionality has been surprisingly scarce (cf., Tabossi, Fanari, & Wolf, 2008). On account of the paucity of effective experimental means, little has been known about the neural mechanism of Chinese idiom processing. Our study into the online processing of Chinese idioms differing in compositionality is expected to deepen our understanding of the linguistic phenomenon of idiomaticity. In this paper, as the parameter to describe bottom-up adding of semantic values of constituent parts in a linguistic construction, compositionality is tentatively employed as a criterion for classifying Chinese idioms, giving prominence to direct contribution of literal meanings3 to commonly-used idiomatic meanings. By the observation and introspection of a good number of Chinese idioms, we decide to take idioms with the double V þ N grammatical structure to conduct a case study. This type of idioms is a representative in the group of idioms featuring the two-plus-two grammatical structure. Additionally, for the sake of internal validity in experimental designs, the influences exerted by the internal syntactic structure of Chinese idioms should be held constant so as to avoid possible

2 “Compositionality” in the present paper belongs to the semantic category. In some parts of this paper, this term is written as its full form, i.e. semantic compositionality. 3 According to the specific conditions of different parts in the present paper, some terms are used interchangeably with the same connotation, including “literal meaning”, “literal level”, “literal scene” and “literal interpretation”. For the same reason, the illustration applies to alternative terms such as “figurative meaning”, “figurative level”, “figurative scene” and “figurative interpretation”.

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interference caused by the syntactic processing in Chinese idiom comprehension. Taking account of the degree to which the meaning of a character can be perceived to contribute to the stipulated idiomatic meaning of a Chinese idiom, we hereby propose a three-grade hierarchy in which the majority of Chinese idioms fall into three groups differing in compositionality, i.e. Chinese idioms with a high/ medium/low degree of compositionality. Langlotz (2006) employs Idiomatic Activation-Set to refer to the mental network that can be potentially activated in idiom use. The mental status of an idiom is not a holophrastic entity stored in the mental lexicon, but rather a complex symbolic unit with a composite structure. When a Chinese idiom is encountered, the meanings of its four characters and the underlying constructional schema (e.g., double verbal schema) are supposed to be co-activated as substructures, which define the minimum cognitive structure of this Chinese idiom. Compositionality plays the greatest role in attributing the internal complexity of an idiom to the formal dimension of its proper idiomatic activation-set. The components of an idiomatic construction function as “signposts” that coordinate both meaning construction and meaning construal in a usage-context (Langlotz, 2006, p. 90). The composite activation of components serves as a way to provide relevant access to a complex linguistic unit. An idiom is in nature a composite configuration to be cognitively unfolded: the conceptual substructures making up the idiomatic activation-set of this idiom could be optionally activated when it is used. In Chinese idioms with high compositionality, the substructures have been strongly activated to provide a shortcut linking different parts in cognitive structuring, though a part of substructures have been relatively frozen when this idiom was lexicalized.4 All the composite parts at the literal level denote almost the same as what is expressed at the figurative level. The conceptual substructures are firmly bound by the idiomatic activation-set underlying Chinese idioms, and thus provide direct access to the target conceptualization. As a result, the two meaning levels can be identified as an integral whole. As regards Chinese idioms with medium compositionality, most conceptual substructures have been partially, but not fully, pruned from the idiomatic activation-set, which results in a weaker linking schema between the vehicle and the target, i.e. the two levels are virtually asymptotic in their mental status. Insufficiently activated, those substructures of the literal scene have to be pushed to the background, and thus only provide indirect access to the profiled target conceptualization. For these idioms, what they truly refer to are not equal to what it literally means, but derived from some extent of semantic extension with a “distance” in between. Importantly, it is easy for language users to establish direct correspondence between meanings of characters and some parts of idiomatic meanings. Conceptual similarities between substructures in this idiomatic activation-set facilitate to a certain degree the meaning construction of these Chinese idioms. In Chinese idioms with low compositionality, nearly all their conceptual substructures at the literal level have been completely cutoff from the idiomatic activation-set and derived of the possibility of being activated, let alone establish perceptible correspondence between the parts in the vehicle and the target. The profiled literal scene is no longer needed as the conceptual scaffolding to construe the meaning encoded in the target. The conceptual disparity between the two meaning levels seems insurmountable. Other resources such as the etymological basis of these Chinese idioms have to be resorted to if language users would like to reproduce the association from which the idiomatic interpretation was originally activated. Despite its feasibility in theory, compositionality is in nature an effect of conceptual structuring and cognitive construal rather than a mere linguistic term. In fact, idiom processing involves a cascade of mental processes, which wait to be validated by empirical methods. With high temporal resolution, the ERP technique provides a good channel to probe into online linguistic processing. In the current experiment, two ERP components (the N250 and the N400) are hypothesized to reflect distinct underlying neurocognitive processes involved in Chinese idiom comprehension and are suited for quantitatively unraveling the dynamic nature of idiom comprehension and assessing effects of compositionality in this process. Posner et al. postulated a model for visually presented words in which meaning access takes place at approximately 250 ms in the left anterior cortex (Abdullaev & Posner, 1998; Posner & Pavese, 1998; as

4 For example, the constructional schema has been largely fixed, not allowing of any exchange of the positions where the two paratactic verbal schemas are located.

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cited in Hinojosa, Martin-Loeches, & Rubia, 2001). For linguistic processing, the N250 was tentatively labeled for the appearance of a negative-going wave peaking at around 250 ms post-target onset in the masked repetition priming paradigm5 (Holcomb & Grainger, 2006). Broad in scalp distribution, this negativity has the largest effects over the midline and slightly frontal LH regions. Moreover, it was suggested that this component reflects the processing of English letters and letter clusters, with its amplitudes correlated with the degree of mismatch between mental representations activated by primes and those activated by targets. Subsequent studies (Grainger, Kiyonaga, & Holcomb, 2006; Holcomb & Grainger, 2007; Kiyonaga, Grainger, Midgley, & Holcomb, 2007; Morris, Frank, Grainger, & Holcomb, 2007) supported such functional significance of the N250 by suggesting an early influence of prelexical orthographic representations in target word comprehension. In other words, the N250 can be differentially sensitive to early sublexical processing involved in identifying relative positions of a word’s constituent letters as an ordered letter combination, which are used to generate access to the whole-word orthographic representations (Holcomb & Grainger, 2006). Results of these ERP experiments have provided converging evidence that the N250 can reflect processing at the formlevel underlying visual word recognition. The N400 amplitudes are inversely related to many linguistic parameters, such as predictability (expectancy) of a word in a given context (Kutas & Hillyard, 1984), the degree of contextual constraint on experimental stimuli (Van Petten, Kutas, Kluender, Mitchiner, & McIsaac, 1991), the ease of semantic integration of words into a prior context (Holcomb, 1993; Van Petten, Coulson, Rubin, Plante, & Parks, 1999). It has been a dominant opinion that the N400 is sensitive to postlexical integration, in which the word is semantically integrated with its preceding context (Holcomb, 1993; Van Petten et al., 1999). Moreover, it is reported that this component can reflect the ease of accessing information from the longterm memory (Kutas & Federmeier, 2000). The N400 effects obtained in semantic priming were described during presentation of word pairs (Bentin, McCarthy, & Wood, 1985), in which its amplitudes were reduced for the targets related to prime words as compared to those unrelated to the prime. Besides, Frank, Judith, and Hubertus (2001) believed that the N400 amplitude can be an inverse function of the expectancy degree for some words to be presented in a predominant semantic context. Results obtained in the masked repetition priming paradigm have suggested that this component varies chiefly as a function of the integration between whole-word orthographic and higher-level semantic representations, i.e. interactivity at the form-meaning interface (Holcomb & Grainger, 2006, 2007; Holcomb, O’Rourke, & Grainger, 2002; Holcomb, Reder, Misra, & Grainger, 2005; Kiyonaga et al., 2007; Morris et al., 2007). It has also been shown that the N400 component can be modulated by both automatic and controlled processing as an index of priming effects (Kiefer, 2002; Kutas & Federmeier, 2000). The amplitude of the N400 is additionally thought to be a function of essential mental resources to reach the threshold where the lexical representation can be searched out from the mental lexicon (Wei & Luo, 2002, p. 175). Kiyonaga et al. (2007) investigated the time course of cross-modal interactions in word recognition and suggested that within-modality (e.g., visual-visual) repetition priming shows modulations of amplitudes of both the N250 and the N400, and the properties remain fairly stable across tasks and prime duration, while cross-modal (e.g., visual-auditory) repetition priming proved to be highly sensitive to even a very small change in prime duration. Despite disagreement about interpreting the direction of ERP effects with regard to underlying cognitive processes, it is generally assumed that increased negativity could reflect more processing efforts (Holcomb & Grainger, 2007). The consensus applies specifically to the N250 (form-level processing) and the N400 (semantic-level processing) for the present purpose of elucidating the feasibility of compositionality in Chinese idioms.

5 The masked repetition priming paradigm is often used to study visual word recognition. It includes the rapid sequential presentation of a series of visual stimuli: a forward mask (e.g., a series of hash marks ######), a prime (a word), a backward mask (another row of hash marks) and a target stimulus, to which subjects are asked to make a judgment. Sandwiched between the two masking stimuli and very briefly displayed, the primes are imperceptible often for subjects. But the primes can still produce robust effects on subsequent processing, in that the processing of masked primes interacts with the stream of processes involved in recognizing the targets (Holcomb & Grainger, 2007).

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2. Method 2.1. Participants A total of 18 self-designated right-handed undergraduates (8 male, 10 female) from Xuzhou Normal University (Jiangsu Province, East China) volunteered to participate in the ERP experiment. They were all native speakers of Mandarin Chinese and were completely unaware of the purposes of the present experiment. None of them had participated in any of the three pencil-and-paper pretests. All the subjects had at least one year of college education, with no reading disabilities or neurological/psychiatric impairment. They all had normal or corrected-to-normal vision as established by self-report. They were tested individually and were paid for their participation. The data of 3 participants were discarded in the statistic analysis due to excessive EEG artifacts. This left 15 subjects (6 male, 9 female; age range 20–24 years, mean ¼ 21.87 years, SD ¼ 1.06) who generated sufficient quality EEG data for further analysis. 2.2. Rating studies for experimental stimuli An original set of 216 Chinese idioms with the double V þ N grammatical structure were selected as the basis for constructing the linguistic stimuli for the later ERP experiment. Four dimensions, i.e. familiarity, literality, compositionality and context, have been shown to be influential during idiom processing, in which compositionality is taken as the independent variable. In the first written questionnaire of rating studies, 40 undergraduates were required to rate their familiarity with these Chinese idioms listed on a piece of paper through a 5-point scale that ranges from 1 (quite unfamiliar) to 5 (highly familiar). Idioms scoring at least 4 by more than 95% of the subjects (i.e., an idiom with an average score  3.85) were singled out for the later studies.146 idioms satisfying the inclusion criteria were sieved out through this procedure (see Appendix I). For literality, another group of 40 students (including 15 postgraduates) were required to evaluate the plausibility of the literal interpretations of the already picked-out Chinese idioms and to check whether the constructed literal interpretations can be applied to those idioms according to the their linguistic intuition as native speakers of Chinese. The literal interpretations were constructed on the basis of the literal meanings of idioms provided in the classic Dictionary of Chinese Idioms (1987). If the literal interpretation was too long, we adjusted to more or less the similar length on the premise that its literal meaning cannot be changed. For example, the Chinese idiom “pao zhuan yin yu” has the literal interpretation of “cast a brick to attract jade” (Figurative meaning: offer a few commonplace remarks by way of introduction so that others may come up with valuable opinions) which is provided by the Dictionary of Chinese Idioms. All the interpretations were allowed to be modified if the participants could provide some better ones. In the third pretest, the dimension of compositionality was rated by a new group of 40 students with similar background of education compared to the previous two groups. These participants were given the 146 Chinese idioms paired with their refined literal interpretations. Again through a 5-point scale ranging from 1 (not related) to 5 (very related), the participants were requested to assess the degree to which these literal interpretations were semantically relevant to those commonly-used meanings of corresponding Chinese idioms, i.e. to what degree can the idiomatic meanings of the 146 Chinese idioms be inferred from their literal interpretations. After the three pretests, we managed to obtain 146 Chinese idioms differing in compositionality but meanwhile with fairly high familiarity and literality. As explicated above, the Chinese idioms with different degrees of compositionality constitute a continuum. However, for the sake of classification, two cutoff points had to be chosen so as to divide this continuum into three separate parts. 15 idioms with comparatively inconsistent ratings (SD > 1.08) and 23 idioms with scores between two parts were excluded as the marginal ones. In this way, all the Chinese idioms to be taken as linguistic stimuli in the subsequent ERP study fell into three categories that differ in compositionality (i.e., high, medium, and low). The average scores for the linguistic stimuli with high, medium and low compositionality were 4.57, 2.97 and 1.76 respectively (see Appendix II). Finally, 108 Chinese idioms (36 for each degree of compositionality), 36 non-idiomatic phrases and 48 filler idioms constitute the final experimental stimuli. The non-idioms (i.e., literal phrases), used as the control group, do not include those four-character habitual expressions termed quasi-fixed phrases (cf., Zhou, 1997), such as duan cha dao shui (serve the tea and fill cups with water). Characterized by the same grammatical structure, all the 108 idioms as well as the 36 non-idiomatic phrases were to be involved in

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further ERP statistic analyses. Mixed in the linguistic materials to be examined, fillers are Chinese idioms with other types of grammatical structures to avoid potential confounding effects related to the repetition of the only grammatical structure. All these fillers would not be employed in further analyses, but were equivalent in status to the other four target types from the subjects’ perspective (see Appendix III). 2.3. Experimental procedure The whole experiment was conducted in a sound-attenuated, electrically-shielded chamber where the subjects were seated on a comfortable chair in front of a 17-inch computer screen located approximately 120 cm from their eyes. The subjects were offered instructions prior to performing their experimental task. They were required to read all the presented sentences silently and then try to understand the four-syllable target idioms or phrases following them. Each participant should response as quickly and as accurately as possible whether a target was semantically relevant to the meaning of the preceding priming sentence, indicating their judgments by pressing corresponding buttons on the response device. The left button corresponded to “Yes” and the right one to “No”. The percentages of correct “Yes” and “No” responses were 50% respectively. “Yes” and “No” buttons (left vs. right) were counterbalanced across subjects. The importance for subjects to maintain their gaze on the center of the screen throughout the experiment was emphasized, both during the pretest instructions and before resuming testing after each rest break. All prime-target pairs were presented in a pseudo-randomized order so as to make sure: (a) trials of the same type were not to be consecutively presented in more than three; and (b) at least 40 trials intervened between repetitions of the same target idiom or phrase. All the linguistic stimuli were presented word-by-word at the center of the screen. The stimuli were displayed in silvery texts against a black background at moderate contrast. All characters were presented in the SIMSUN font with the 60 font size. Each trial began with the presentation of a string of four hash marks (####) displayed at the center of the screen for 300 ms, followed by a 500-ms blank screen, indicating the onset of a trial. Each word was presented for 300 ms with a 100-ms interstimulus interval (ISI), i.e. the stimulus onset asynchronies (SOA) was 400 ms. When all the priming words of one trial have been presented, there was a 2300-ms blank screen before the onset of the fourcharacter target. Each target, either an idiom or a phrase, was displayed for 300 ms. The reaction window for subjects to press the buttons was 1500 ms. A new trial started after an inter-trial internal (ITI) of 3000 ms. All stimuli were presented in 6 blocks, each containing 64 trials. Before the formal experiment blocks, 20 illustrative prime-target trials not included in the study proper were provided for warm-ups. Through this procedure, all subjects were able to familiarize themselves with the performance task. The total duration of the ERP experiment was approximately 50 min with time for a break between two blocks. Each experimental session lasted up to about 1.5 h, including technical preparations for recording the EEGs (Fig. 1). 2.4. EEG recording The EEGs were continuously recorded with 64-channel Ag/AgCl electrodes held in place on subjects’ scalps by an elastic cap through AC-coupled high input impedance amplifiers (200 kU, Net Amps). EOGs were recorded bipolarly with four electrodes placed above and below the left eye (vertical) and at the two outer canthi (horizontal). Amplified analog voltages (0.05–100 Hz band-pass) were sampled at 1000 Hz. All electrode impedance was kept below 5 kU. ERP analyses consisted in averaging EEG segments in synchronization with the onset of the target idiom or phrase in each trial over an 1100 ms period including a 100-ms pre-stimulus interval. The left mastoid voltage was used as the reference. Ocular artifacts were monitored, and the subjects’ horizontal, vertical eye movements as well as blinks were corrected off-line with an automatic algorithm. The recorded signals were low-pass filtered at 30 Hz and were rescaled across the average reference. The EEG epochs were baseline-corrected to the first 100 ms. All the epochs resulting in a correct answer were carefully scanned and the remaining artifacts were rejected before being averaged to give individual and grand-mean ERPs. All the presented linguistic stimuli and behavioral responses were designed, controlled and recorded by Scan 4.3 running on a Dell-compatible computer. “Triggers” synchronized with the stimulus and response

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Fig. 1. Example trials in this ERP experiment.

events were also sent by this software, allowing the timing for task-related events and behavioral responses to be included simultaneously with EEG recording (Fig. 2). 3. Results 3.1. Visual inspection of ERPs As can be seen in the ERP plots displayed in Fig. 3(A) and (B) and Fig. 4(A) and (B), an initial negative potential at about 70 ms is followed by a negativity peaking at about 160 ms. After these early components, the most distinguishing feature of the ERP waveforms emerges, i.e. a negative-going deflection with a peak near 250 ms. This negativity was identified as the N250 component, with its amplitudes showing differential values to different types of linguistic stimuli. In general, non-idioms have elicited the largest N250, whereas Chinese idioms with high compositionality have hardly produced a noticeable curve. The N250 amplitudes induced by Chinese idioms with medium and low compositionality have been between that induced by the former two types. Within idioms, the amplitudes of the N250 are inversely graded by the degrees of compositionality. The voltage maps (Fig. 5(A)–(C)) indicate that the N250 has its largest effect in frontal brain areas, a bit favoring the LH sites. This scalp distribution is basically in accord with previous findings on this ERP component based on Western languages. An additional fronto-centrally distributed negative-going deflection (Fig. 6(A)– (C)), identified as the N400,6 occurs between about 350 and 550 ms post-target onset. The largest N400 is similarly induced by non-idioms, whereas those amplitudes for Chinese idioms are still inversely related with their compositionality degrees. In some sites, ERP waveforms of two adjoining types (e.g.,

6 The dominant scalp distribution of the N400 in the present study is slightly different from the classic distribution of this component based upon European languages. Nevertheless, it has been postulated that the distribution of the N400 might not be identical for phonograph and ideograph (Wei & Luo, 2002, pp. 171–172).

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Fig. 2. Electrode montage used for the current ERP study

Chinese idioms with high and medium compositionality) overlap. At most sites, N400s are followed by several negative deflections. In the end, the ERP waveform goes in a direction almost parallel to the baseline, neither turning positive nor returning toward the baseline. 3.2. Data analysis In order to investigate the N250 and the N400 components, the electrodes showing the largest effects for each type of target stimuli were selected to analyze the data of mean amplitudes and latencies of the two ERP components. The N250 was examined by analyzing its data on 16 electrode sites (i.e., AF3, AF4, F1, F2, F3, FZ, F4, F5, F6, FC1, FC2, FC3, FCZ, FC4, FC5, FC6) in the anterior cortex between 230 and 290 ms, for three contiguous time windows of 20 ms each so as to quantify the time course of the ERP effects. In the same way, ERP data of the N400 on 18 electrode sites (i.e., F1, F2, FZ, F3, F4, FC1, FC2, FCZ, FC3, FC4, C1, C2, CZ, C3, C4, CP1, CPZ, CP2) located in the fronto-central cortex were measured between 360 and 460 ms, for two contiguous time windows of 50 ms each. Behavior data (RTs and accuracy) were also analyzed with compositionality as the single factor. Geisser and Greenhouse (1959) correction was applied to all the repeated measures with more than one degree of freedom (corrected p values are reported). The significance level in the study was set at p  .05. 3.2.1. Behavioral data All correct responses in the reaction window were included in behavioral analyses. As shown by the repeated-measures one-way ANOVA, subjects responded with different times to different types of linguistic stimuli [F(3, 42) ¼ 15.224, p < .001]. It is revealed that subjects responded significantly more slowly to non-idiomatic literal phrases than to all Chinese idioms, [non7 vs. high: F(1, 14) ¼ 16.977,

7 For the sake of simplicity, target types are sometimes written as high (Chinese idioms with high compositionality), medium (Chinese idioms with medium compositionality), low (Chinese idioms with low compositionality), and non (non-idiomatic literal phrases).

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Fig. 3. ERPs time locked to target onset of the four stimuli types for the N250: (A) ERP plots in 8 electrode sites; (B) blowup of FZ site from (A).

p ¼ .001; non vs. medium: F(1, 14) ¼ 20.941, p < .001; non vs. low: F(1, 14) ¼ 30.974, p < .001]. However, no significant difference was found between idioms of different compositionality degrees, [high vs. low: F(1, 14) ¼ .562, p ¼ .466; medium vs. low: F(1, 14) ¼ .655, p ¼ .432; high vs. medium: F(1, 14) ¼ 4.486, p ¼ .053]. In other words, subjects seemed to respond marginally more slowly to Chinese idioms with high compositionality than they did to those idioms with medium compositionality.

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Fig. 4. ERPs time locked to target onset of the four stimuli types for the N400: (A) ERP plots in 12 electrode sites; (B) blowup of CZ site from (A).

Accuracy differences were significant across all the four types [F(3, 42) ¼ 3.126, p ¼ .041] and across Chinese idioms of three degrees of compositionality [F(2, 28) ¼ 4.469, p ¼ .024]. It is also revealed that subjects were significantly less accurate in identifying the semantic relevance between the priming sentences for target idioms with low compositionality as compared with the primes for target idioms

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Fig. 5. Voltage maps calculated from difference waves of the N250: (A) high minus non; (B) medium minus non; (C) low minus non.

with high compositionality [F(1, 14) ¼ 5.237, p ¼ .038] and those for targets with medium compositionality [F(1, 14) ¼ 7.337, p ¼ .017]. Accuracy differences between the other target types did not reach statistical significance (ps > .08). In general, accuracy was comparatively high in each type, notwithstanding these differences. Table 1 displays mean reaction times (RTs) and percentage of errors (PEs) for behavioral responses in each of the four target types in the present ERP study. 3.2.2. Electrophysiological data As mentioned above, to directly compare compositionality effects in processing Chinese idioms, we use repeated-measures ANOVAs to analyze ERP data accrued on two within-subjects variables, i.e. compositionality (4 levels: high, medium, low, non) and electrodes (16 levels for the N250, 18 levels for the N400). 3.2.2.1. N250 epoch (230–290 ms). 230–250 ms. Analyses of ERP data in this time window yielded no significant main effects of compositionality across all the four types of stimuli [F(3, 42) ¼ 2.617, p ¼ .078], nor within the three types of idioms [F(2, 28) ¼ 1.183, p ¼ .319]. The only presence of a main effect occurred between idioms with high compositionality and non-idioms [F(1, 14) ¼ 17.128, p ¼ .001] while there was additionally a significant Compositionality  Electrode interaction effect [F(15, 210) ¼ 2.576, p ¼ .039].

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Fig. 6. Voltage maps calculated from difference waves of the N400: (A) high minus non; (B) medium minus non; (C) low minus non.

250–270 ms. Analyses of ERP data in this time window confirmed our observation of Fig. 3 that the N250 amplitude varies inversely as one function of compositionality. A significant main effect was found both across all the four stimuli types [F(3, 42) ¼ 8.069, p ¼ .001] and across the three types of idioms [F(2, 28) ¼ 4.519, p ¼ .031], but no interaction effect was yielded [across four types, F(45, 630) ¼ 1.900, p ¼ .077; across three types, F(30, 420) ¼ 1.129, p ¼ .353]. Follow-up analyses by contrasting every two types indicated that the effects of compositionality were mostly significant both across the four types and between the idioms [high vs. medium: F(1, 14) ¼ 6.811, p ¼ .021; high vs. low: F(1, 14) ¼ 7.561, p ¼ .016; high vs. non: F(1, 14) ¼ 32.060, p < .001; medium vs. non: F(1, 14) ¼ 10.328, p ¼ .006], but the N250 amplitudes between some types still did not differ significantly from each other [medium vs. low: F(1, 14) ¼ 1.134, p ¼ .305; low vs. non: F(1, 14) ¼ 2.201, p ¼ .160]. There were not any significant interactions between idioms [high vs. medium: F(15, 210) ¼ 1.616, p ¼ .184; high vs. low: F(15, 210) ¼ .950, p ¼ .427; medium vs. low: F(15, 210) ¼ .819, p ¼ .534], but the interactions differed between two types of idioms and non-idiomatic phrases [high vs. non: F(15, 210) ¼ 3.926, p ¼ .005; medium vs. non: F(15, 210) ¼ 2.312, p ¼ .050 (marginally significant)]. 270–290 ms. Analyses of data in this time window indicated a highly significant main effect of compositionality across all the four types of targets [F(3, 42) ¼ 7.165, p ¼ .002], with an interaction effect of approaching significance [F(45, 630) ¼ 1.943, p ¼ .075]. Within idioms, the main effect did not reach significance [F(2, 28) ¼ 1.922, p ¼ .171]. Despite that the compositionality effects did not

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Table 1 Mean RTs (milliseconds) and PEs (%) for all the four target types with standard deviations (SD) in parentheses.

Mean RTs Mean PEs

High

Medium

Low

Non

511.32 (55.23) 2.41 (2.75)

497.99 (55.94) 2.41 (2.07)

505.37 (64.41) 5.00 (3.35)

557.38 (67.44) 3.33 (3.35)

differ significantly within the idioms (ps > .110) in follow-up analyses, it is revealed that there were highly significant differences between the non-idioms and idioms [high vs. non: F(1, 14) ¼ 16.955, p ¼ .001; medium vs. non: F(1, 14) ¼ 14.051, p ¼ .002; low vs. non: F(1, 14) ¼ 4.678, p ¼ .048], whereas the interaction effects also reached significance [high vs. non: F(15, 210) ¼ 3.617, p ¼ .012; low vs. non: F(15, 210) ¼ 2.863, p ¼ .034] with one exception [medium vs. non: F(15, 210) ¼ 1.670, p ¼ .176]. Latency. Analyses of data that measure peak latencies of the N250 in the time window spanning 230–290 ms demonstrated that there were highly significant differences in regard to latency both across the four types of targets [F(3, 42) ¼ 37.506, p < .001] and across idioms of varying degrees of compositionality [F(2, 28) ¼ 13.539, p < .001]. Additional analyses contrasting all adjoining types showed that most differences in latency reached highly significant (ps < .01) except that between high and medium [F(1, 14) ¼ .755, p ¼ .399]. There were no significant interaction effects in all contrasts (ps > .366). Table 2 summarized mean latencies of the N250 within this time window between 230 and 290 ms for the four types of targets. It is apparent that the higher degree of compositionality with which Chinese idioms are, the earlier an N250 crest they will induce. Moreover, non-idioms produced a peak significantly later than idioms. 3.2.2.2. N400 epoch (360–460 ms). 360–410 ms. Analyses of data in this time window did not yield any significant effects of compositionality, neither across the four types of target stimuli [F(3, 42) ¼ 1.556, p ¼ .223] nor within the three types of idioms [F(2, 28) ¼ .630, p ¼ .520]. In the follow-up analyses, it was found that the main effects failed to reach significant difference due to compositionality, with only a marginal level between idioms of medium compositionality and non-idiomatic phrases [F(1, 14) ¼ 4.132, p ¼ .061]. There were no interaction effects involving both the factors of compositionality and electrode sites (ps > .074). 410–460 ms. Analyses of data in this time window demonstrated significant effects of compositionality across the four stimuli types [F(3, 42) ¼ 3.351, p ¼ .034], whereas the effects approached marginal difference within idioms [F(2, 28) ¼ 2.921, p ¼ .077]. Once again, no Compositionality  Electrode interaction effects were yielded within the two contrasts [four-level: F(51, 714) ¼ 1.272, p ¼ .275; three-level: F(34, 476) ¼ 1.451, p ¼ .209]. On the sequence of target types shown in Fig. 5(A) and (B), all adjoining types did not statistically differ from each other (ps > .108), but in every two types with at least another type in between there were evident differences [high vs. low, F(1, 14) ¼ 4.677, p ¼ .048; high vs. non: F(1, 14) ¼ 7.611, p ¼ .015; medium vs. non: F(1, 14) ¼ 6.053, p ¼ .027]. The differences caused by interactions were not nearly as apparent (ps > .092) (Table 3). 4. Discussion The purpose of the current study is to confirm the feasibility of compositionality as a criterion for sorting Chinese idioms, and in particular, to give a temporal measure of the dynamic meaning

Table 2 Mean latencies (milliseconds) of the N250 for all the four target types with SD in parentheses.

Mean latencies

High

Medium

Low

Non

242.35 (3.24)

243.60 (2.82)

253.18 (2.53)

270.58 (2.58)

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Table 3 Main effects of semantic compositionality: statistical significance for comparisons between every two types of targets. Epoch (ms)

High vs. medium

High vs. low

Medium vs. low

High vs. non

Medium vs. non

Low vs. non

N250 230–250 250–270 270–290 Latency

p > .3 p < .03* p > .1 p > .3

p > .1 p < .02* p > .1 p < .01**

p > .6 p > .3 p > .6 p < .01**

p < .01** p < .01** p < .01** p < .01**

p > .1 p < .01** p < .01** p < .01**

p > .2 p > .1 p < .05* p < .01**

N400 360–410 410–460

p > .5 p > .7

p > .6 p < .05*

p > .2 p > .1

p > .09 p < .05*

p > .06 p < .05*

p > .4 p > .7

*The difference is significant. **The difference is highly significant.

construction in processing Chinese idioms of different types, and to examine the pattern of compositionality effects within this process. Results of this study will be discussed in several analytical tools in combination with functional significance of the N250 and the N400 accrued in the experiment. An interim model specified for Chinese idiom comprehension will then be tentatively proposed. In the N250 time window, especially during the second and third epochs, non-idiomatic phrases generated significantly more negative amplitudes than idioms. Among the three types of idioms varying in compositionality, there was a significant linear trend for the N250 amplitudes, whereby idioms of low compositionality generated the largest amplitude, idioms of high compositionality the smallest, and idioms of medium compositionality in between. Moreover, ERP data of mean latencies of the N250 for different types of target stimuli also showed a linear trend, with peak latencies increasing with the decrease of compositionality in idioms, while the N250 enticed by nonidiomatic phrases peaking significantly later than all the idioms. The topographical distribution of the N250 in the LH frontal cortex, which is somewhat similar to that reported by some previous studies (e.g., Hinojosa et al., 2001; Holcomb & Grainger, 2006), enlightens us to infer that this component observed in the current study reflects early sublexical processing (including orthographic and phonological processing) of target idioms or phrases. The N250 is hypothesized to reflect the ease of access from letter combinations to whole-word orthographic identification, in that the presentation of a cluster of English letters which is not as ordered as word representation was shown to result in an N250 amplitude increase, as compared to that evoked by repetition of a prime word8 (Holcomb & Grainger, 2006). Besides, Swinney and Cutler (1979) thought that semantic judgment tasks could lead to comparatively early recognition processes, which further strengthens our inference. Following such an account, we are guided to consider the N250 one index of a preliminary processing of the four target stimuli. Importantly, for most characters in the Chinese language, the interrelationships between its orthography, phonology and meanings are inseparably intricate (Wei & Luo, 2002, pp. 196–197). In other words, the combination of several Chinese characters will always give rise to a meaning, even if it is not “meaningful” in the case when a mismatch occurs between their positions and that in the mind of language users. The N250 elicited by the presentations of Chinese idioms or phrases would reflect in some measure a state of resonance between mental representations of subcomponents that comprise these target stimuli (i.e., Chinese characters and their syntagmatic relations) and their whole-lexical representations. In Langlotz’s (2006) terms, it is the substructures immanently associated with an idiomatic activation-set represented by an idiom that are co-activated to different extents whenever the idiom is encountered. Given that the

8 Although tentative statements of functional significance of the N250 were made on the basis of the paradigm of masked repetition priming, the stability of the effects of this component in the visual modality (Kiyonaga et al., 2007) has made it possible to generalize its significance to some other cases.

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substructures of individual constituents (the four characters in Chinese idioms) come into play at a lower level, i.e. at the sublexical level, while mental configurations of idioms are accessed at a higher level, i.e. at the lexical level, the N250 amplitude can be seen as an inverse function of activation strength of component substructures in Chinese idioms at a formal dimension of an idiomatic activation-set, which pertains to a mapping from internal complexity of idioms to their composite structures. One more theoretical claim deserving our attention here is Giora’s GSH (1997) which has been verified by Laurent, Denhières, Passerieux, Iakimova, and Hardy-Baylé (2006). According to the GSH, the lexicalized meanings of familiar idioms enjoy a processing priority. In other words, the idiomatic meanings of the idioms employed in our study, salient as they are, have been accessed in the preliminary processing. In this sense, the N250 is presumably a reflection of the notion of compositionality in that its amplitudes vary due to changes of contributing mappings from the meanings of individual Chinese characters to initial access to idiomatic meanings in this very time window (Posner et al.; as cited in Hinojosa et al., 2001). The organic trinity of orthographic, phonological as well as semantic features in Chinese characters, i.e. distinguishing characteristics of ideographs makes it plausibly deducible from the pattern of the N250 effects to differential modulations for Chinese idioms with different degrees of compositionality with regard to interactivity between sublexical and lexical form representations. It should also be pointed out that the cognitive mechanism of suppression and enhancement (Gernsbacher & Robertson, 1999; Gernsbacher, Keysar, Robertson, & Werner, 2001) has an important role between the two representation levels. When the target idioms or literal phrases were presented, their most salient meanings (i.e., idiomatic meanings of idioms and literal meanings of non-idioms) were initially accessed; meanwhile, some interference was caused by the activation of extraneous information. For Chinese idioms with high compositionality, their conceptual substructures were strongly coactivated that the two representation levels almost coincided with each other. Therefore this general mechanism functioned little to attenuate inappropriate meanings. However, individual substructures in Chinese idioms with low compositionality were in large part pruned from the mental network of their idiomatic activation-sets, bringing about a situation in which idiomatic and literal meanings were competing for being retrieved. It was thereby necessary to suppress these idioms’ literal meanings, which were dependent upon contextual information, whereas their idiomatic meanings could be strengthened. The extra consumption of mental resources in this process resulted in increases of the N250 amplitudes. Quite interesting is the fact that what is said and what is meant coincide in both idioms with high compositionality and non-idioms. But the N250s induced by the two target types were poles apart, the former the smallest but the latter the largest. It allows us to speculate that the largest negativity of the N250 to literal phrases agrees also with the hypothesized formal identification. Compared with idioms which have already fixed their constructional schemas in the mental lexicon of proficient speakers, these temporarily created phrases do not occupy any specific node in the mental network of Cognitive Grammar (Langacker, 1987). This leads to the most negative N250 peak generated by them, for subjects had to consume more mental resources to identify a four-character combination as an acceptable one; a semantic judgment was meanwhile underway. Mean latencies of the N250 for all the types provide additional evidence bolstering the existence of an “idiomatic key” postulated in the Configuration Hypothesis (Cacciari & Tabossi, 1988). Within Chinese idioms, the increase of peak latencies with the decrease of compositionality might be primarily due to the rise of difficulties in projecting distributed meanings of characters to the saliently-coded, commonly-used meanings in a simultaneous process of recognizing their entrenched and ordered forms. But it took longer in the case of non-idioms because the mind needed some extra time to evaluate the acceptability of such combinations of characters in a linguistic unit. This explanation may also apply to the differences of RTs because subjects apparently responded more slowly to non-idiomatic targets than they did to idioms. Such a reaction delay to non-idioms could be explained as due to more time needed to search out appropriate nodes for targets of this type in the mental network, while idioms’ entrenched nodes could simplify this process. These data, plus clear interaction effects between idioms and nonidiomatic phrases in the epoch between 250 and 270 ms with an absence of main effects of compositionality, suggested that the processing loci on the cortex for Chinese idioms and non-idioms might be different. Furthermore, the most noticeable N250 effects in the LH frontal cortex appear

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to be supported by some rTMS (Fogliata et al., 2007) and fMRI studies (Mashal, Faust, Hendler, & Jung-Beeman, 2008; Romero Lauro, Tettamanti, Cappa, & Papagno, 2007), which concluded that the prefrontal cortex (minimally) has a specific role in retrieving idiomatic meanings of idioms and literal meanings of non-idioms. As with the N250 analyses, the comparison of the main effects of compositionality during the second epoch of the N400 time window (i.e., 410–460 ms) revealed another presence of a significant linear trend, with effects for Chinese idioms of high compositionality the smallest and non-idiomatic phrases the largest. The graded effects of the N400 might suggest the occurrence of a qualitatively different mental process. In fact, this ERP component is, as documented by previous studies, usually subject to contextual constraints, especially at the dimension of postlexical processing (e.g., Frank et al., 2001; Holcomb, 1993; Van Petten et al., 1991, 1999). Allowing for the semantic priming paradigm adopted in the ERP experiment and the comparatively long prime-target interval, the N400 modulations here could well reflect influences of priming sentences on expectancy for certain Chinese idioms. When subjects had read a priming sentence, there was probably an implicit expectation in their mind for possible targets to be presented during the blank-screen interval. Considering the comparatively high familiarity of all the idiom targets, such an expectation could facilitate a later comparison between the meaning of an actual target and that of the prime itself. In other words, the amplitudes of the N400 across the four types are correlated with the priming effects. After a preliminary processing as revealed by the N250 at the sublexical-lexical interface, meaning construction has gradually turned from initial access to the most salient meanings to other less salient ones which well matched the primes. This turning could be seen as subsequent processing. Divergent meanings were manipulated by Gernsbacher et al.’s mechanism of suppression and enhancement (1999, 2001) again for a contextappropriate meaning, compatible with the priming sentence. That is, the N400 could have a graded rise in proportion to decreasing roles played by the less salient meanings, i.e. literal interpretations of idioms. In addition, it should be noted that such an account seemed somewhat ineffective in nonidioms due to the fact that the largest N400 was elicited by non-idioms. But this result could justify itself by subjects’ inability to predict what a specific phrase of this type would be presented, unlike in other cases when they could basically tell what a specific Chinese idiom would be presented when given a prime. Therefore, the N400’s differential sensitivity to Chinese idioms with different compositionality should be mainly attributed to their figurativeness, i.e. the semantic association between two levels of interpretations, whereas it is the predictability in the prior context that drives such ERP effects between idioms and non-idioms (Kutas & Hillyard, 1984). Besides, such an inference was supported by the behavioral results: with respect to RTs, the sharp contrast between idioms and nonidioms with an absence of differences within idioms suggested the existence of different processing mechanisms for the two main categories; the apparently more errors in subjects’ performing of the experimental task for Chinese idioms with low compositionality as compared to other target types further backed growing discrepancies between “bipartite conceptualization” (Langacker, 1987, p. 92) with the decrease of compositionality. The overall pattern of relatively high accuracy rates could be interpreted as due to the task in the present experiment being quite easy. An alternative possibility is that the expectancy effects brought about by priming sentences could be accompanied by the shaping of a specific conceptual structure, i.e. image component9 (Dobrovol’skij & Piirainen, 2005). As a bridge linking what is said and what is meant, image component could be considered as the medium in comparing two meanings of divergence to different degrees. Given the comparable literality of all Chinese idiom targets in this study, their image components should play a role on the same plane. Therefore, the intensity of a motivating link between such a level and the other conceptual level represented by those stipulated figurative meanings in postlexical integration could be reflected by the N400 amplitude. Again, we should note that the notion of image component serves as one of design features to distinguish figurative lexical units (e.g., Chinese idioms) from nonfigurative lexical units (e.g., non-idioms utilized in this study) (Dobrovol’skij & Piirainen, 2005, p. 13), which explains why converged meanings between literal and figurative levels for Chinese idioms of

9 Image component refers to a specific conceptual structure which is assumed to mediate between the lexical structure and the actual meaning of a figurative unit, such as an idiom (Dobrovol’skij & Piirainen, 2005, p. 5).

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high compositionality resulted in attenuation of the N400 amplitude, whereas it was not the case for non-idiomatic phrases. Moreover, similar N400 effects have been reported in some studies into metaphor processing, in which greater N400 amplitudes were induced by metaphors than by literal expressions (Coulson & Van Petten, 2002; Pynte, Besson, Robichon, & Poli, 1996). Hence, linguistic units with two conceptual structures should have a specific processing mechanism. In this sense, the above two explanations for the N400 effects could be reconciled. Another explanation for the cognitive mechanism underlying the graded N400 priming effects differs much from the above accounts of interactions between an integrated meaning accrued in postlexical processing and the meaning accrued in a priming sentence. Instead, it presumably follows the hypothesis that early processing proceeds at the form level and modulates the N250, while later processing at the meaning level shows strong modulations of the N400 (Holcomb & Grainger, 2006, 2007). Put it another way, the N400 was thought to be a reflection of the mapping from whole-word representations onto lexical semantics.10 However, as discussed above for functional significance of the N250, once the form of a Chinese idiom has been recognized, its semantic representations at the lower level (e.g., its literal meaning) have to be quickly suppressed to make way for the higher-level semantic representations, which leaves little time for the processing to rest at the literal level. Therefore, the sensitivity of the N400 to integration at the formmeaning interface seems spurious for Chinese idioms. The necessity of such integration has been ruled out, due to the ideographic nature (the organic whole of orthography, phonology and semantics) of Chinese characters. On a final note, the scalp distribution of the N400 component in the research seems to be more anterior than the typically posterior maximum. Nevertheless, there is no reason to expect such a difference in the topographical distribution would invalidate our results and we hold that this very component is a member in the N400 family. In fact, it remains a much debated issue of the neural generators of this language-related ERP component. For example, McCarthy, Nobre, Bentin, and Spencer (1995) provided clear evidence of an N400-like activity in the left anterior-medial temporal cortex. Moreover, Luo and Wei (1998) proposed that the N400 scalp distributions for ideograph and phonograph may not be the same. It is worth noting that our N400 maximum during its second epoch overlaps basically with the brain areas reported in a previous fMRI study (Romero Lauro et al., 2007) and might suggest progression of semantic integration with the dominant context. Taken together, all the above findings suggest that processing of Chinese idioms (with comparatively high familiarity and literality) involves at least two main phases under the condition of silent reading, i.e. an interactive processing involving both prelexical form representations and higher-level lexical or semantic representations, followed by postlexical semantic integration with the prior context. When a four-character Chinese idiom is presented to a proficient Chinese speaker, the first work the neural/brain mechanism requires him/her to do is to retrieve the corresponding node occupied by such a lexical unit from an elaborate mental network that has taken shape in long-term memory. Given the highly uniform four-character form of most Chinese idioms, a language user’s primary attention is allocated for judging the internal structure of the presented idiom rather than its external form. The node is localized when such a combination of four characters has been recognized as a perfect match for an ordered character combination entrenched in the mental lexicon. When the form identification is underway, the literal meanings of the four characters as well as their syntagmatic relations are activated. In this manner, this node could be bipartitely activated, one at a higher level of holistic orthographic representation for the very idiom, the other at a lower level of sublexical representation for its individual substructures. The former is readily accessible to the commonly-used meaning of the Chinese idiom, in that this meaning is saliently-coded and contextindependent. A simultaneous mapping from the lower level to the higher-level ends this preliminary phase by reflecting different contribution given by individual characters to idiomatic meanings (as

10 Different from this hypothesis, Niznikiewicz and Squires believed that the N400 is impervious to neither phonological nor orthographic differences, but rather an important index of semantic processing (as cited in Wei & Luo, 2002, p. 174).

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shown by different modulations of the N250), and promotes meaning construction to the next phase. Then comes the subsequent processing, in which the contextual information is favored. Rather weakly constrained by contexts in the preliminary processing, meaning construction in this phase becomes orderly and highly sensitive to priming sentences. It adjusts itself to a “groove” constructed by predominant contextual information. The construction of a contextually-appropriate meaning results from an integration process that deactivates other contextually-inappropriate meanings. In this fashion, a Chinese idiom gives top-down feedback as influenced by the priming effects, i.e. postlexical integration. The difficulty of such a process is dependent on the divergence between the meaning accessed in its preliminary processing and that meaning derived from the prior context. Thus, the degree of compositionality Chinese idioms with affects their semantic integration in postlexical processing (as shown by different modulations of the N400), which drives what is meant by this Chinese idiom to reach a consensus with the context in which it is used. It should be stressed that this processing model is only tentatively suited for highly familiar and literally plausible Chinese idioms,11 in that it is built up on the basis of ERP correlates of compositionality through a limited number of linguistic data. Nevertheless, we have at least come to one sound conclusion: the compositionality dimension can exert clear impacts on the comprehension of Chinese idioms and has proved to be a feasible parameter in their classification. 5. Conclusion Primed by literal interpretations, 146 Chinese idioms of varying compositionality have been demonstrated to elicit clearly graded wave crests, as reflected by two ERP componentsdthe N250 and the N400. Compared with the N400, the N250 was not predicted before the present study and was rarely reported in studies based on Western idioms. Through a detailed discussion based upon statistical analyses of behavioral responses and ERP data, the dimension of compositionality has been demonstrated to exert a great influence on Chinese idiom processing. The results of this study present evidence of psychologically relevant differences among Chinese idioms varying in the dimension of compositionality, and support the view of their different representation. A heuristic model minimally for the comprehension of Chinese idioms was proposed, as including early form recognition coinciding with preliminary meaning access, followed by later semantic integration with the dominant context. In summary, the current ERP study provides a reliable foundation for validating the Compositional Hypothesis (Glucksberg, 1993, 2001) that the meanings of individual characters remain cognitively active and accessible in the process of Chinese idiom comprehension, as a background of conceptual comparison for idiomatic meanings. Familiar Chinese idioms are in nature “sleeping” metaphors rather than “dead” ones. It supports the cognitive-linguistic view of gradual reduction of metaphorical strength in the lexicalization of idioms. Furthermore, access to stipulated meanings of Chinese idioms has been verified to be a function of the degree of compositionality that idioms possess. Acknowledgments The research was supported by grants from the National Social Science Foundation of China (06BYY019) held by Hui Zhang and the National Natural Science Foundation of China (30740040) held by Yiming Yang. The paper is also supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions and Major Program of National Social Science Foundation of China (10 & ZD126).

11 Some Chinese idioms are literally implausible, such as san chang liang duan (three long, two short; unexpected misfortune or accident) fall beyond our scope of empirical materials because we can hardly give any plausible literal interpretation for them, even after attempts to find out the internal logical relations hidden behind the characters. These idioms are seen as folk expressions without a high degree of classicism (Zhou, 2004, p. 242).

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Appendix I. Familiarity indices of 216 Chinese idioms

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Appendix II. Compositionality indices of target idioms

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Appendix III. Linguistic materials used for targets

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