The development of reading skills in second language (L2) learners who are exposed to different writing systems poses a significant challenge due to the need to integrate the cognitive abilities involved in both higher-level processes (such as proficient language use, reading strategies, conceptual understanding, and background knowledge) and lower-level processes like word recognition, which includes phonological and orthographic processing. Numerous studies have demonstrated that L2 reading can be influenced by various factors, including the age of acquisition, task requirements, and level of L2 proficiency (for more information, see the review by Li et al., 2023; Tatsuno and Sakai, 2005). A longstanding area of interest in research on L2 reading is whether the neural mechanism remains consistent between first language speakers (L1Ss) and second language learners (L2Ls), or if it is influenced by the characteristics of different writing systems.

The Chinese writing system,¹ a logographic system, is significantly different from alphabetic systems such as English and Indonesian, because there is essentially no strict grapheme-to-phoneme mapping in Mandarin (Chen and Shu, 2001; Tan and Perfetti, 1998). One of the most learner-friendly features of the Indonesian writing system is its phonetic consistency. Each letter in the Indonesian alphabet generally corresponds to a specific sound, and the spelling closely matches the pronunciation. This makes reading and writing in Indonesian relatively easier compared to English, where phonetic inconsistencies are more common. In addition, each letter in the word “cat” in English and the word “buku” (meaning “book”) in Indonesian directly corresponds to its phonetic representation. In contrast, the visual form of Chinese characters (such as “猫” for “cat” or “书” for “book”) does not provide direct information about pronunciation. Thus, for L1 speakers of alphabetic languages to read Chinese characters requires high demands on visuospatial processing and relies heavily on memorizing the relationships between visual forms and their pronunciation or meanings (Ge et al., 2006; Huang et al., 2004; Tan et al., 2005).

The distinct properties of writing systems have been widely supported by unique brain activation patterns. For instance, when reading alphabetic words, the left inferior frontal lobe and left temporal-occipitoparietal junction are activated. On the other hand, reading Chinese characters activates the left lateral middle frontal cortex and other regions in the right hemisphere, such as the inferior occipitotemporal cortex (Bolger et al., 2005; Tan et al., 2001, 2005). This dual-sided effect suggests that visual areas in the right hemisphere may help in the spatial processing necessary for the layout of Chinese characters. A recent study by Zhang et al. (2023) found that despite significant differences in orthographic features between Chinese and Mongolian, the event-related potential (ERP) of lexical items in both languages differed substantially from pseudowords in the parietooccipital scalp region. This suggests that a similar neural mechanism is involved in early word processing across different writing systems, consistent with prior research (Chee et al., 2000; Yang et al., 2011).

Word recognition has long been considered a strong indicator of L2 reading development. According to the Convergence hypothesis (Green, 2003), the brain network of L2 learners gradually aligns with that of L1 learners as proficiency in the L2 language increases. Several studies have provided evidence supporting a positive correlation between the level of L2 proficiency and the operation of a shared neural network (Cao et al., 2013; Hernandez et al., 2007; Yang et al., 2011). For instance, high-proficiency L2 learners are more efficient in word recognition compared to low-proficiency L2 learners (Stein et al., 2009) (see review by Cao et al., 2022). While many empirical studies have explored the impact of proficiency on L2 reading (Cao et al., 2013; Chee et al., 2000; Liu et al., 2006; Stein et al., 2009; for a comprehensive review of recent research, see Cao et al., 2022), few studies have delved into the real-time visual specialization of advanced L2 learners of Chinese whose native language is alphabetic.

This study aims to investigate whether advanced L2 learners process different writing systems in overlapping or separate cerebral systems during real-time word recognition. Specifically, the study seeks to determine if advanced L2 learners of Chinese, with Indonesian as their L1 (an alphabetic language), can achieve native-like word recognition. To address this issue, this study uses online measures of brain activation with high temporal resolution to decipher real-time brain responses to stimulus presentation. Previous studies showed that as the brain starts retrieving lexical and semantic information simultaneously (Hauk et al., 2012), the N170 (a negative ERP component with a peak latency of approximately 140–180 ms post-stimulus) becomes indicative of word recognition (Bentin et al., 1999; Maurer et al., 2006; Rossion et al., 2003). Additionally, a plethora of studies have shown that when processing Chinese scripts, the N170 exhibits greater left-lateralization compared to right-lateralization (Yum et al., 2014; Zhao et al., 2012).

The next section begins with an introduction to visual specialization and the main ERP components relevant to word recognition, followed by an overview of experimental studies, especially ERP studies, on the impact of L2 proficiency on Chinese word recognition, concluding with the current ERP study.

The first step in word recognition includes the visual analysis of the printed script, characters, and layout. While processing specific forms, the human brain can differentiate human faces or visual words from a series of visual stimuli. This ability is known as visual specialization and is indicated by the N170 (e.g., Maurer et al., 2005; Rossion et al., 2003; Schendan et al., 1998). Current findings related to the N170 in visual perception mainly fit into two categories.

First, when compared with non-orthographic stimuli, word stimuli trigger enhanced amplitude and lateralized N170 in the left hemisphere (Fu et al., 2012; Kim et al., 2004; Kim and Kim, 2006; Maurer et al., 2006). Rossion et al. (2003) utilized pictures of faces, objects (cars), and English words to investigate the human brain’s ability to categorize objects in the early stages of visual processing, finding that the N170 induced by words significantly differed from that induced by objects, with words eliciting a left-lateralized N170 and objects eliciting a bilateral one. Fu et al. (2012) observed that faces elicited a larger and later N170 response compared to characters, with characters showing a more left-lateralized N170 response. To explore the N170 response to characters across different hemispheres, Zhao et al. (2012) asked participants to determine whether the colors of four types of stimuli (Chinese characters, cartoon faces, line drawings, and stroke combinations) matched those in the previous grid display. Their findings indicated that in the left hemisphere, the N170 response to Chinese characters was significantly stronger than that to other types of stimuli. However, there was no notable difference in response to Chinese characters compared to non-orthographic stimuli, except for line drawings. Conversely, in the right hemisphere, the N170 responses to Chinese characters did not significantly differ from those to non-orthographic stimuli, with the exception of line drawings. These findings suggest that the heightened N170 response to Chinese characters in the left hemisphere could serve as an indicator of proficiency in reading Chinese.

Besides, the amplitude and left-lateralization of the N170 reflect expertise in reading scripts. Alphabetic scripts systematically elicit left-lateralized N170 responses in skilled readers (Maurer et al., 2005), while the N170 has been reported to be left-lateralized in response to logographic stimuli such as Chinese characters (Cao et al., 2011; Lu et al., 2011; Maurer et al., 2008; Yum et al., 2018), and also as showing a bilateral or right-lateralized distribution (Xue et al., 2008; Yum et al., 2011). Wong et al. (2005) conducted a recall judgment task in which both English monolinguals and Chinese-English bilinguals were asked to determine if the presented character matched the previous one or if the underlined character in the current string was a repeat from the previous string. The results showed that Chinese-English bilinguals had enhanced N170 responses for both Roman alphabets and Chinese characters compared to pseudofonts, whereas English monolinguals displayed a greater N170 amplitude for Roman letters compared to Chinese characters and pseudofonts. This mixed lateralization of N170 may be due to varying task demands (Hauk et al., 2012).

To investigate the commonality and particularity of brain activation by different writing systems in bilingual individuals, Kim & Kim (2006) explored differences and similarities among brain activation during visual perceptions of Korean, English, and Chinese words, wherein participants were native Korean speakers who had received more than 6 years of education in both Chinese and English. All Chinese used in their design were one-character Chinese, and the Chinese and Korean words had the same pronunciation as well as the same meaning. The reaction time data showed that the average response time was the shortest for Korean, followed by English, and the longest for Chinese, with significant differences observed only in the comparison between Korean and Chinese. They also found a left-lateralized N170 when Korean and English words were processed, but the left-lateralization was not significant for Chinese characters. In comparison, Yum et al. (2011) found that when processing their native language, both English L1 speakers and Chinese L1 speakers showed a left-lateralized N170 response, while English monolinguals exhibited a right-lateralized N170 when processing Chinese characters.

In addition to the N170 component, the ERP component P100 peaks at approximately 100 ms after the stimulus and is immediately followed by the N170 effect, which helps us determine and extract the time window of early lexical processing. The P100 component indicates cortex activity in response to orthographically atypical objects in the occipitotemporal area. It is considered the onset of the N170 effect (Hauk et al., 2006; Takamiya et al., 2020; Yum et al., 2015). The amplitude of the P100 can be influenced by physical features of visual stimuli (e.g., contrast, luminance, size) and age (Brem et al., 2006), as discussed in the review by Tong et al. (2016). Yum et al. (2018) observed a left-lateralized P100 for native Cantonese spearkers and a right-lateralized P100 for intermediate traditional Chinese learners during the detection of radical position violations (Radicals refer to recurrent subcharacter components), suggesting that the detection of radical position violations may involve global character structure representations in intermediate L2Ls. The variations in the L1 background of the participants in Yum et al. (2018) may have confounded the existing results.

Perfetti and Liu (2005) and Perfetti (2007) argued that the activation pattern in the brain when learning a new language with a different writing system can be explained by accommodation (where individuals use existing reading network procedures in acquiring a new writing system) and assimilation (where new procedures are used to read in the new writing system by individuals). The differences in design principles between the Chinese writing system and alphabetic scripts in terms of orthography-to-phonology mapping have long fascinated researchers.

To date, the correlation between accommodation/assimilation and L2 proficiency remains mixed in L2 Chinese reading, with some studies favoring accommodation (e.g., Chinese-English, Cao et al., 2011) and others favoring assimilation (e.g., Chinese-English, Deng et al., 2008) (for a review of recent research, see Sun et al., 2015). These results suggest the need for further investigation into whether advanced L2 learners, whose native language is alphabetic, recognize Chinese characters at an early stage of lexical processing and whether they recruit the same brain activation patterns as native Chinese speakers. Meanwhile, it was found that English words, Chinese pinyin (an alphabetic Chinese script), and Chinese characters use the same brain network in both orthographic search and semantic classification tasks (Ding et al., 2003). Accommodation is further supported by the fact that late and early Chinese-English bilinguals use the same network when processing Chinese and English (Chee et al., 2000; Yang et al., 2011), as well as by multilanguage contrast studies (e.g., Spanish, English, Hebrew, and Chinese in Rueckl et al., 2015).

In comparison, assimilation also holds theoretical significance (Leonard et al., 2010). Liu and Perfetti (2003) observed that the peak latencies of the N150 and N250 were earlier for Chinese words than for English words. They also noted that English words (L2) caused reduced activity in the right visual cortex compared to Chinese characters (L1). Cao et al. (2011) found that high proficiency in late English–Chinese bilinguals was associated with increased brain activation in three regions (the right superior parietal lobule, the right lingual gyrus, and the left precentral gyrus) in lexical decision tasks, but this correlation did not appear when writing in pinyin. Therefore, exploration of brain activation patterns during word recognition across different writing systems, as well as the impact of proficiency on the utilization of brain regions in bilingual reading, is necessary.

Based on the studies discussed above, the inconsistency in their results primarily stems from uncontrolled factors that affect the processing of Chinese scripts. Firstly, word recognition efficiency and accuracy can be impacted by previous exposure. Only a few studies (Yum et al., 2011) included participants who were native non-logographic speakers (e.g., native English speakers) with no prior exposure to Chinese, leaving the relationship between N170 lateralization and language proficiency unclear. Secondly, the early stages of visual word recognition can be significantly influenced by the writing system and task demands. In alphabetic scripts, grapheme-phoneme mapping automatically activates and takes precedence over other processing methods like semantic processing.

On the other hand, orthography-to-phonology mapping in Chinese is less transparent, requiring specific attention for other processes to activate (Zhao et al., 2012). Participants engaged in explicit reading and semantic tasks may introduce phonological and semantic activation, potentially affecting early visual processing (Strijkers et al., 2015; Wang and Maurer, 2017). According to Perfetti and Tan (1998), the order of access to lexical information in Chinese character identification starts with the graphic, then proceeds to the phonological, and finally to the semantic. Zhao et al. (2012) argued that the lateralization of N170 may be more influenced by top-down task modulation for Chinese scripts compared to alphabetic scripts. So far, a study using an implicit lexical decision task has not been conducted on the recognition of Chinese characters by L2Ls of Mandarin, but this approach could minimize the influence of phonological and semantic awareness activation.

The current study aimed to investigate the early-stage visual word recognition in Chinese L2 learners whose native languages use alphabetic scripts, through a delayed-color matching task. Two empirical predictions were made below:

Prediction 1: high-level L2Ls have the potential to reach proficiency levels equivalent to those of native speakers in the early stages of Chinese character processing. Specifically, we predict that the P100 and N170 responses evoked by Chinese characters will be greater than those evoked by line drawings.

Prediction 2: high-level L2Ls may exhibit ERP components that are indistinguishable from those of native adults. Specifically, we anticipate that, for both native speakers and advanced L2Ls, the N170 elicited by Chinese characters in the left hemisphere may be significantly greater than in the right hemisphere, while the N170 component triggered by line drawings may not differ between the hemispheres. Otherwise, the P100 and N170 observed in native speakers may differ from those observed in advanced L2Ls.

The current study aimed to investigate the visual specialization of advanced Chinese L2Ls at an early stage by using a delayed color-matching task. The results of the ERP analysis suggest that second language learners can reach a level of visual specialization comparable to that of native speakers. Specifically, second language learners are able to perform rapid and automatic visual specialization of Chinese characters, even with the unique addition of brain activation patterns.

This study provides support for the potential of advanced second language learners (L2Ls) to exhibit native-like visual specialization of Chinese characters, as demonstrated by the brain topology seen in the left-lateralized N170 response to Chinese characters. The left-lateralization of N170 is a significant indicator of visual specialization for words, distinct from the N170 effects seen for faces and objects, which often exhibit bilateral or right-lateralized patterns (Bentin et al., 1999; Maurer et al., 2005; Rossion et al., 2003). Essentially, the left-lateralized N170 represents a specific neural response to words, demonstrating the brain’s unique sensitivity to linguistic stimuli. Just as Yum et al. (2014) found that bilingual learners with high efficiency in vocabulary tasks showed a significant increase in left-lateralized N170, while bilingual learners with low efficiency in vocabulary tasks exhibited a distinct right-lateralized increase in N170 amplitude, our study also reveals that advanced L2Ls who frequently read Chinese characters in their daily lives exhibit a consistently left-lateralized N170 response to Chinese characters, similar to native Chinese speakers. Maurer et al. (2007) proposed that the repeated practice of grapheme-phoneme decoding in visual word recognition during the process of learning to read is responsible for the left-lateralized N170 associated with visual specialization. Therefore, our results suggest that advanced L2Ls are capable of developing grapheme-phoneme mapping in response to characters.

One possible explanation could be the familiarity with the stimuli used, which is a result of significant reading experience, as indicated in previous studies (Cao et al., 2011; Maurer et al., 2008; Tong et al., 2016; Yum and Law, 2021). For instance, Xue et al. (2019) conducted a study comparing the neural mechanisms of native Chinese reading when individuals read Chinese characters and cursive Chinese characters. The results of the ERP showed that only printed characters elicited the left-lateralized N170, while cursive characters evoked a bilateral N170 response. This difference may be attributed to the need for greater familiarity with cursive characters in terms of visual perception. A similar familiarity effect was also noted in L2 reading (Maurer et al., 2008), where Japanese L1 speakers exhibited a left-lateralized N170 when processing Japanese hiragana and katakana,³ while English L1 speakers showed a bilateral N170 effect. Therefore, visual familiarity resulting from reading experience and proficiency could also play a role in the left-lateralization of the N170.

Although our findings demonstrate that advanced L2 learners can achieve a level of visual specialization similar to that of L1 speakers, it is crucial to note that their brain topography was not completely identical to that of L1 speakers. In contrast to previous studies (Cao et al., 2011; Maurer et al., 2008; Tong et al., 2016; Yum and Law, 2021), we found that among the L2 learners, the N170 response elicited by Chinese characters in the right hemisphere showed a significant difference compared to that elicited by line drawings, whereas this significant difference was not observed in the L1 speakers. Previous research has shown right-lateralized or bilateral visual expertise effects for both novel objects and faces (Bentin et al., 1999; Rossion et al., 2003; Cao et al., 2011; Maurer et al., 2010). However, we argue that, due to the use of an implicit color-matching task aimed at minimizing top-down modulation in the current study, the L2 learners recognized the Chinese characters through a pre-existing expertise network (McCandliss et al., 2003; Nelson et al., 2009). These findings suggests that the underlying neural mechanism for reading in L2 is still influenced by their first language and its writing system.

The P100 component reflects the early and rapid processing of both simple and complex stimuli, laying the groundwork for visual specialization (Maurer et al., 2005, 2006; Zhao et al., 2014). This component is influenced by top-down modulation, with variations in latency and amplitude depending on the research paradigm and task requirements (Segalowitz and Zheng, 2009; Taylor, 2002). The absence of top-down modulation may account for the results obtained in our current study. Unlike previous studies (Segalowitz and Zheng, 2009; Yum et al., 2018), we conducted a delayed color-matching task and found no significant differences in P100 between Chinese characters and line drawings. This difference may be due to variations in research paradigms, as the delayed color-matching task reduces the impact of top-down processes on a variety of stimuli and diminishes the potential for phonological and semantic activation (Zhao et al., 2012).

Interestingly, after a stimulus presentation of 200 ms, the N250 evoked by Chinese characters was greater than that evoked by line drawings for both the L1s and the L2s. The N250 reflects the mapping of prelexical formal representations to orthographic representations (Holcomb and Grainger, 2006). These findings inspire us to focus on the orthographic processing of Chinese learners in our future research.

This study discovered that advanced Chinese L2 learners with native backgrounds in an alphabetic script exhibit significant visual specialization and a predominant distribution of left-lateralization, with some activation in the right hemisphere. The results suggested that the spatiotemporal cortical activation of advanced L2 learners is similar to that of Chinese native speakers, although the influence of their pre-existing expertise network (first language and its writing system) persists.

However, this research can be further explored. Firstly, this study focused solely on the real-time word recognition process of advanced Chinese L2 learners without comparing the mechanisms involved among learners at different proficiency levels. Secondly, this study only included native speakers of alphabetic languages, but did not compare the neural mechanisms underlying their reading of Chinese characters with those of L2 learners whose first languages have varied logographic systems. Thirdly, while the experiment controlled for readability and familiarity of the linguistic stimuli, it did not investigate the potential impact of unfamiliar characters on the early stage of lexical decisions in advanced L2 learners.