Word-to-text integration: ERP evidence for semantic and orthographic effects in Chinese

https://doi.org/10.1016/j.jneuroling.2016.11.010Get rights and content

Highlights

  • Chinese reading employed an immediate word-to-text integration as English.

  • Parallel with English, morphemic effects were not found in Chinese reading either.

  • Orthographic form repetition effect was specifically functional in Chinese reading.

  • Word-to-text integration is general across writing systems but different in details.

Abstract

Although writing systems affect reading at the level of word identification, one expects writing system to have minimal effects on comprehension processes. We tested this assumption by recording ERPs while native Chinese speakers read short texts for comprehension in the word-to-text integration (WTI) paradigm to compare with studies of English using this paradigm. Of interest was the ERP on a 2-character word that began the second sentence of the text, with the first sentence varied to manipulate co-reference with the critical word in the second sentence. A paraphrase condition in which the critical word meaning was coreferential with a word in the first sentence showed a reduced N400 reduction. Consistent with results in English, this N400 effect suggests immediate integration of a Chinese 2-character word with the meaning of the text. Chinese allows an additional test of a morpheme effect when one character of a two-character word is repeated across the sentence boundary, thus having both orthographic and meaning overlap. This shared morpheme condition showed no effect during the timeframe when orthographic effects are observed (e.g. N200), nor did it show an N400 effect. However, character repetition did produce an N400 reduction on parietal sites regardless it represented the same morpheme or a different one. The results indicate that the WTI integration effect is general across writing systems at the meaning level, but that the orthographic form nonetheless has an effect, and is specifically functional in Chinese reading.

Introduction

Reading comprehension involves integrating a word, as it is read, with the meaning of the previous text and thus updating the mental representation of the text (Gernsbacher, 1990, Kintsch, 1988). Accordingly, the Reading Systems Framework (Perfetti & Stafura, 2014) places word meaning in a central role in comprehension: it is the output of word identification system and the input into the comprehension systems. In this framework the integration of a word's meaning into the reader's current understanding of the text is a key recurring process in reading. From these recurring processes, comprehension occurs incrementally, building a mental model of the text and using that model to continue the integration process. It is this process of word-to-text integration (WTI) that is our focus here. In particular, we examine how this process works in Chinese reading, given key differences between written Chinese and written English. Differences between reading Chinese and reading English appear at the word identification level because of writing-to-language mapping differences between alphabetic and Chinese writing (Perfetti, Liu, & Tan, 2005). At the level, of comprehension, after accounting for writing system influences on word identification, one expects more universal comprehension processes to prevail.

As a processing concept, word-to-text integration (WTI) is the set of meaning related processes that leads to the understanding of word—while it is read—in relation to the preceding text. While these integration processes occur continuously within a sentence, a particular focus of the WTI paradigm is the integration processes that occur across a sentence boundary. This boundary condition on WTI allows a clearer focus on incremental comprehension of text, as opposed to the comprehension of a sentence. The incremental updating processes across and within sentence boundaries may differ in the support they receive from memory-based integration processes as opposed to prediction. Specifically, predictive processes and memory-based integration processes both occur continuously to bring about WTI. But across a sentence boundary, predictive processes are weaker than they are within a sentence. Memory-based integration becomes the main mechanism for incremental updating (Stafura et al., 2015, Calloway and Perfetti, 2016, Submitted for publication).

Research on WTI in English has used ERPs, in particular the N400 and the late positivity response (LPR), as indicators of integration (Perfetti and Stafura, 2014, Stafura et al., 2015, Yang et al., 2007). The N400, a negative component at centro-parietal sites that peaks around 400ms after the onset of a word, has been well established as a marker of meaning congruence between a stimulus and its preceding context (Kutas and Federmeier, 2011, Kutas and Hillyard, 1980). In a sentence, the predictability of a word has a strong influence on the N400, which becomes relatively more positive when the word is predictable.

In cross-sentence boundary text comprehension, the WTI paradigm has focused on the first content word across the boundary. Thus, the N400 amplitude is reduced on this cross-boundary word when readers are presented with short stretches of two-sentence texts (Yang et al., 2005, Yang et al., 2007).

For example, Yang et al. (2007) presented texts such as the following:

  • a.

    Referentially explicit: After being dropped from the plane, the bomb hit the ground and exploded. The explosion was quickly reported to the commander.

  • b.

    Referentially paraphrased: After being dropped from the plane, the bomb hit the ground and blew up. The explosion was quickly reported by the commander.

  • c.

    Baseline: Once the bomb was stored safely on the ground, the plane dropped off its passengers and left. The explosion was quickly reported to the commander.

When the first sentence established an event (exploded/blow up) that could serve as an antecedent for the first content word of the second sentence (explosion), the N400 on the critical word “explosion” was more positive compared to the baseline (no referent for critical word “explosion”). Especially interesting for text comprehension is that N400 deflection was as great for the paraphrase effect, where there was no morpheme overlap across the sentence boundary (“blew up. The explosion”) as when there was shared morpheme across the boundary (“exploded. The explosion”). This paraphrase effect suggests that the cross boundary reduction in the N400 reflects meaning integration, rather than word repetition. A study by Stafura and Perfetti (2014) found the strength of word association across the sentence boundary did not influence the paraphrase effect, further supporting the interpretation that the WTI paraphrase effect was about meaning integration.

Writing systems influence word identification processes, as shown by comparisons of Chinese and English (Perfetti et al., 2005). Such influences, if full absorbed at the level of orthographically based word identification, should be absent in comprehension, which is dependent on linguistic and cognitive processes. The integration processes in WTI would then be general across different writing systems. However, it is possible that orthographic factors have a continued effect on “downstream” meaning processes when, as in Chinese, they directly express morpheme at the character level. The nonalphabetic Chinese character system allows a basic morphemic/orthographic unit—the character—to convey meaning information within a word in a very transparent way. The fact that each character is a morphemic orthographic unit allows us to observe transparent morpheme effects across a sentence boundary.

Although morphological processes play a role in visual word identification across languages, they are particularly important in Chinese as orthographic units. In alphabetic writing, the strategy for detecting morphology has been to try to separate morphology from orthography. Morphological decomposition occurs on frequently occurring morphemic units, producing morpho-orthographic segmentation at early stage (Lavric et al., 2012, Morris et al., 2008, Rastle et al., 2004).

The situation is different in Chinese, where the major orthographic unit is a meaning bearing morpheme. English spacing makes words easy to see but morphemes not so easy to see. Chinese spacing reverses this situation—difficult to see words, easy to see morphemes. Chinese words may have one, two, and three or more characters, with two-character words being the most frequent. For example, 花园 (garden) is composed of two morphemes: 花 (flower) and 园 (garden). The abundance of such compound words suggests an important role for morphological awareness in Chinese children's literacy development (Liu and McBride-Chang, 2014, Wu et al., 2009). Words that share morphemes are identified more readily and with reduced fixation time (Yen et al., 2008, Zhou et al., 1999). Relevant for our ERP study is evidence that the N200 component in central and parietal regions reflects the early morphemic orthography overlap in Chinese compound word recognition (Du et al., 2013, Du et al., 2014, Jia et al., 2013, Zhang et al., 2012).

Important is this additional fact: In a Chinese two-character word, each character contributes a morpheme to the meaning of the word. A second word can share one of these characters while being either closely related in meaning to the first word or unrelated in meaning to the first word. For example,花销 (“expense”) and花费 (“cost”) are meaning related and share the character “花” (“ spend”); 花园 (“ garden”) and花费 (“cost”) have the same character “花” but their meanings are unrelated (This character means “flower” in the first word and “spend” in the second word). Thus this character represents different morphemes in the two words, a single orthography and pronunciation associated with different meanings. Thus, we can ask whether, in addition to a word-related effect across a sentence boundary, there is also a morphemic meaning effect that is independent of orthography. A shared morpheme may accelerate word identification and word meaning access, leading to rapid integration of word meaning with prior text. Alternatively, because reading comprehension and word identification have different processing demands, it is possible that only word identification is sensitive to an orthographic morpheme. Integration in reading comprehension may depend directly on word meaning rather than on both morpheme meaning and word meaning.

Thus, the goals of our study are, first and most generally, to determine whether cross boundary word-to text integration effects extend to Chinese, a language and writing system very different from English. Second and more specifically, to determine whether a distinctive property of Chinese writing—the orthographic conveyance of morpheme information through a character within a two-character word—has a role in mediating word-to-text integration. If the effects of orthographic mapping are limited to word identification without affecting integration processes, then the WTI results for Chinese should pattern with those of English: An effect of word meaning congruence across a sentence boundary with no additional effect of orthography. However, if an orthographic morpheme serves as a retrieval cue in meaning integration, then WTI in Chinese should be affected by whether an orthographic character repeated across a sentence boundary conveys related or unrelated meanings across the sentence boundary.

These alternatives lead to the following predictions. If the orthographic morpheme plays a role in WTI, then a character repeated across a sentence boundary conveys the same morpheme to the two words, we expect see an additional reduction of the N400 beyond that produced by the paraphrase condition, which allows integration at the word meaning level without character overlap. However, when the character does not have the same meaning across the boundary, we expect a more complex mix of facilitation (from orthographic form repletion) and inhibition effects (from incompatible meanings). Finally, if the orthographic morpheme is not functional in integration beyond its contribution to word identification, then there should be no additional effect of a repeated character with the same meaning beyond that of meaning related words.

The experiment measures WTI on the first word of a second sentence, while manipulating the availability of information in the first sentence. The first sentence varies the characteristics of its final two-character word as follows: In a paraphrase condition, the two words across the sentence boundary have related meanings but share no characters (and thus no morphemes). This corresponds to the paraphrase condition in the English language experiments. In a condition of morpheme repetition, the two words share a character that is the same morpheme (orthography +, morpheme +, O+M+). In a condition of character repetition without morpheme repetition (orthography +, morpheme-, O+M-), the two words across the boundary share the same character, but the character does not convey the same morpheme. In a baseline condition, the two words across the boundary share no characters and are unrelated in meaning. Table 1 shows examples.

Comparisons of the paraphrase and O+M+ conditions with the baseline condition test the paraphrase effect—that related meanings support integration and produce an N400 reduction. Comparisons of the paraphrase and O+M+ conditions test the orthographic morpheme effect. To verify that the any orthographic morpheme effect is due to meaning rather than form, we compare O+M+ with O+M-. The key measurements are ERP measures—especially the N400, but also the N200 and the late positive complex (LPC)—taken on a two-character word that begins a new sentence across a sentence boundary.

Section snippets

Participants

Thirty-two Chinese native speakers (age range from 18 to 35 years) from the University of Pittsburgh and Carnegie Mellon University were paid for their participation in the experiment. Participants were all from mainland of China and proficient in English as a second language, they had TOEFL scores of at least 85 or IELTS scores of at least 7.0. All participants were right handed with normal or corrected-to-normal vision and without any history of head injury or neurological diseases. Each

Behavioral results

Average comprehension accuracy of sentences was high across all four conditions at 95%, with no reliable condition differences, F(3,93) = 1.34, p = 0.27.

N200 component

Mean amplitudes in the N200 window were unaffected by the experimental condition. Thus the early phases of word identification, where sensitivity to orthographic factors might be expected, were not affected by the appearance of a character in the preceding sentence. At central sites, repeated measures ANOVA failed to show a main effect of

Discussion

The current study examined the influence of writing system on word-to-text integration processes in a study of Chinese reading that can be compared with results from English. A key result is that Chinese text comprehension employed immediate integration of word with the meaning of the text, as found in English. A second result was that a contribution of orthographic form emerged for Chinese reading.

Conclusion

Comprehending Chinese, as in comprehending an alphabetic language, requires the reader to integrate the meanings of words, as they are read, with the meaning of the preceding text held in memory. Although integration is not always triggered by the first word across a sentence boundary, when the meaning of that word activates memory for the recently read text, word-to-text integration occurs immediately. This integration is reflected in ERP components measured on the word across a sentence

Acknowledgements

This research was supported by United States NICHD Grant R01HD058566-02 to Charles A. Perfetti and China National Social Science Foundation 15CYY020 to Lin Chen. The authors are grateful to Kim Muth, Hannah Legerwood for help in carrying out experimental sessions.

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