L2 frequency of multiword units

Frequency represents the prevalence of a linguistic unit in the input and indicates the amount of experience one has with the unit (Tremblay & Tucker, Reference Tremblay and Tucker2011). The more frequent the unit, the more likely one encounters it repeatedly. Repeated encounter of a structure makes its representation stronger and more readily accessible in memory; and particularly related to MWUs, high frequency also leads to structure autonomy—that is, being processed as a unit rather than as individual parts (Bybee, Reference Bybee1985, Reference Bybee2006). Empirical research has suggested that more experiences with a MWU, or higher MWU frequency, lead to better learning (e.g., Pellicer-Sánchez et al., Reference Pellicer-Sánchez, Siyanova-Chanturia and Parente2022; Puimège & Peters, Reference Puimège and Peters2020), faster processing (e.g., Ellis et al., Reference Ellis, Simpson‐Vlach and Maynard2008; Yi, Reference Yi2018), and faster production (e.g., Janssen & Barber, Reference Janssen and Barber2012)

Although studies on L2 MWU processing and learning largely confirmed the effects of L2 MWU frequency and congruency, not much is known about how congruency interacts with frequency. Yamashita and Jiang (Reference Yamashita and Jiang2010) hypothesized that congruent MWUs may be less influenced by L2 MWU frequency because they can be accepted based on learners’ L1, whereas for incongruent MWUs, L2 frequency may play a bigger role, as they receive little L1 support. Another possibility is that the congruency effect may attenuate among MWUs of high L2 frequency because as these MWUs are encountered repeatedly, their L2 representations become stronger and are subject to less L1 influence. So far, only Wolter and Gyllstad (Reference Wolter and Gyllstad2013) have examined this potential interaction. Counter to Yamashita and Jiang’s predictions, their results revealed that the congruency effect applied to both high- and low-frequency collocations, and that both congruent and incongruent collocations were subject to L2 frequency influence. Further investigation is needed to understand in what circumstances this interaction may or may not occur. Several studies have suggested that L2 learners’ sensitivity to L2 frequency may vary based on learners’ amount of L2 exposure: more L2 exposure is associated with reduced sensitivity to L2 frequency (Cop et al., Reference Cop, Keuleers, Drieghe and Duyck2015; Yi, Reference Yi2018; Yi et al., Reference Yi, Lu and Ma2017). If learners with different amounts of L2 experiences vary in their sensitivity to L2 MWU frequency, it is possible that these learners’ reaction to congruency is also influenced by L2 MWU frequency to different extents.

Learning context

The previously mentioned bilingual lexicon models by Kroll and Stewart (Reference Kroll and Stewart1994) and Jiang (Reference Jiang2000), in addition to hypothesizing how the L1 and the L2 interact, also provided predictions on how the L1-L2 interaction develops as the L2 learner progresses. Kroll and Stewart (Reference Kroll and Stewart1994) argued that although access to L2 word meanings is mediated by the L1 at the beginning of L2 learning, the connections between L2 words and their meanings will grow stronger and thus reliance on the L1 would decrease when (1) the L2 becomes dominant possibly when learners are in an immersive environment and/or (2) L2 proficiency improves. From a developmental perspective, Jiang (Reference Jiang2000) also argued that as learners’ L2 exposure and proficiency increase, words in their L2 mental lexicon might connect to concepts directly without L1 mediation.

Findings regarding whether an immersive environment reduces L1 influence in L2 learning and processing in general have been mixed so far. In Linck et al. (Reference Linck, Kroll and Sunderman2009), English learners of Spanish, after three months of studying abroad, showed attenuated L1 access in comprehension and production compared with students who learned the L2 in a classroom setting in their home country. Jiang et al. (Reference Jiang, Li and Guo2020) included Chinese learners of English who resided in the US and China. The study revealed that when processing L2 words, only learners in China but not those immersed in the United States exhibited L1 activation. Several studies, in contrast, demonstrated that learners who were immersed in the L2 environment still activated their L1 during L2 processing. Carrol and Conklin (Reference Carrol and Conklin2017), using eye tracking, showed activation of L1 forms but not meanings in L2 idiom processing by Chinese learners of English in the UK. In Thierry and Wu (Reference Thierry and Wu2007) and Wu and Thierry (Reference Wu and Thierry2010), Chinese learners of English in the UK activated L1 translations in the L2 processing of single words as shown by ERP data; however, such L1 activation was not detected in behavior RT data.

With respect to L2 MWU processing, most studies recruited a homogenous group of L2 learners who were residing in their home country or in the target language country. These studies were therefore not positioned to explore the potential moderating effects of learning context on the congruency effect. One exception, Yamashita and Jiang (Reference Yamashita and Jiang2010), compared EFL and ESL learners, who resided in China and the US, respectively, in their processing of adjective-noun and verb-noun collocations. The authors in fact found that only EFL but not ESL learners showed a congruency effect in processing speed, which was interpreted as an indication of ESL learners’ L2 collocation representations being independent of the L1. However, it is not known what aspects—for example the length of residence, age of arrival, or the amount of L2 use—in the immersive environment contribute to the development of L2 MWU representations. Although these variables have been found to affect language learning to different extents in an immersive context (length of residence: e.g., Amuzie & Winke, Reference Amuzie and Winke2009; age of arrival: e.g., Baker, Reference Baker2010; L2 use: e.g., Baker-Smemoe et al., Reference Baker-Smemoe, Dewey, Bown and Martinsen2014; Cubillos & Ilvento, Reference Cubillos and Ilvento2012), they have not been studied in L2 MWU processing. For L2 learners residing in their home countries, it is unclear whether more instruction and/or higher proficiency levels will allow them to eventually develop strong L2 MWU representations like their counterparts in the immersive environment. For the variable of length of instruction, Muñoz (Reference Muñoz2014) suggested that in terms of oral proficiency, nonmmersive learners’ syntactic complexity but not fluency or lexical diversity was predicted by the number of years of formal instruction. Again, this variable has not been explored in MWU processing studies. Regarding L2 proficiency, three studies on L2 collocational processing so far (Sonbul & El-Dakhs, Reference Sonbul and El-Dakhs2020; Wolter & Gyllstad, Reference Wolter and Gyllstad2013; Wolter & Yamashita, Reference Wolter and Yamashita2018) have examined its effect and showed mixed findings. In Sonbul and El-Dakhs (Reference Sonbul and El-Dakhs2020), participants reacted to adjective-noun and verb-noun collocations in a timed AJT task. The authors found an interaction between L2 proficiency and congruency, suggesting that the processing difference in RT between congruent and incongruent collocations was smaller for more advanced learners. This interaction, however, was not found in the untimed multiple-choice test. Wolter and Gyllstad (Reference Wolter and Gyllstad2013), also using an AJT, uncovered an L2 proficiency effect in the accuracy but not RT data: the effect of L2 proficiency was more pronounced on the processing accuracy of incongruent than congruent collocations. Wolter and Yamashita (Reference Wolter and Yamashita2018), on the other hand, did not reveal an L2 proficiency effect: learners displayed a congruency effect regardless of their proficiency. As Sonbul and El-Dakhs (Reference Sonbul and El-Dakhs2020) pointed out, the reason why Wolter and Yamashita (Reference Wolter and Yamashita2018) did not find an effect of L2 proficiency may be because they included proficiency as a categorical rather than a continuous variable; further, the proficiency range included in previous studies was somewhat narrow. Although Sonbul and El-Dakhs (Reference Sonbul and El-Dakhs2020) filled the abovementioned two gaps, their proficiency measure only assessed 1k and 2k levels of vocabulary, which may not have fully revealed participants’ proficiency. The inconsistent findings regarding the effect of L2 proficiency on congruency warrant further research with more comprehensive proficiency measures.

Participants

Thirty-three ESL learners in the US participated in the study. Two of them, who arrived in the US at the age of 6 and 11 years, respectively, and were studying at high school were excluded to make the ESL group more homogenous. The remaining ESL learners all spoke Mandarin as their L1, were studying at university in the US or had graduated from a US university, and were residing in the US at the time of participation. Their mean age was 25.52 years (SD = 5.38, range = 20–42). They had been in the US for at least a year (M = 4.82, SD = 2.13, range = 1.5–12) and came to the US at a mean age of 20.84 years (SD = 5.47, range = 13–36). On a 100-point scale in the language background questionnaire, the ESL learners reported using English 38.10% of their day on average (SD = 22.10, range = 0–81). The proficiency level of the ESL learners was estimated to be at least intermediate-low, given that a TOEFL score of 60 or IETLS of 6.0 is at the lower end of the admission scores required by US universities.

Analysis

All statistical analyses were performed in R (version 3.6.1; R Core Team, 2019). The RT and accuracy data collected from the AJT were analyzed with mixed-effects modeling. Mixed models were built using the lme4 package (version 1.1-21; Bates et al., Reference Bates, Maechler, Bolker and Walker2015). The p values were calculated by lmerTest (version 3.1-0; Kuznetsova et al., Reference Kuznetsova, Brockhoff and Christensen2017). Responses with RTs shorter than 400 ms or longer than 4,000 ms were trimmed using the trimr package (version 1.0.1; Grange, Reference Grange2015). These responses were considered too slow or fast to accurately reflect the genuine recognition process (see also Gyllstad & Wolter, Reference Gyllstad and Wolter2016; Öksüz et al., Reference Öksüz, Brezina and Rebuschat2021; Wolter & Yamashita, Reference Wolter and Yamashita2018, for similar outlier removal criteria). RT trimming affected 0.52% of the ESL data. Trimmed RT data were then log transformed to bring the variable closer to normal distribution.

Log-transformed RTs were analyzed with linear mixed-effects models and only correct responses were included. Generalized linear mixed-effects models were built for accuracy data in which correct responses were coded as 1 and incorrect ones as 0. A maximal model was first built, which included (1) main effects of theoretical interest: L2 collocation frequency, condition (congruent and incongruent), L1 Word1 and Word2 frequencies, age of arrival, length of residence, and L2 use; (2) interactions between the main effects of interest; (3) covariates: collocation length (number of letters), L2 Word1 and Word2 frequencies, and MI; and (4) maximal random-effects structure justified by the data (Barr et al., Reference Barr, Levy, Scheepers and Tily2013). Condition was treatment coded with the congruent condition serving as the reference. Three items (one congruent and two incongruent) were excluded from the analysis because the L1 frequencies of these items were not found in the corpus. In case of nonconvergence, the random-effects structure was simplified by dropping by-subject random slopes first (Barr et al., Reference Barr, Levy, Scheepers and Tily2013), followed by by-item random slopes. The backward stepwise modeling procedure was adopted in which insignificant interactions were first excluded, followed by insignificant covariates. Interactions and covariates that did not improve model fit were then also removed. Models were compared based on the Akaike Information Criterion (AIC), and the model with the lowest AIC was chosen. All continuous independent variables were mean centered to reduce collinearity. The variance inflation factors of the final models were checked using the performance package (version 0.4.0; Lüdecke et al., Reference Lüdecke, Makowski and Waggoner2019) and were all under 10 (Hair et al., Reference Hair, Anderson, Tatham and Black1995). Residuals of the final models were also examined, and observations with a residual greater than 2.5 SD away from the mean were removed. The 95% Wald confidence intervals for estimates were obtained through the confint.merMod() function.

Results and Discussion

Table 2 includes the descriptive statistics of ESL learners’ trimmed RTs (in milliseconds) and accuracy (in percentage) by item type. In response to RQ1 on the congruency effect, the RT analysis (Table 3) showed that overall, ESL learners responded to congruent and incongruent collocations at a similar speed—that is, no congruency effect; in contrast, the accuracy analysis (Table 4) showed that that ESL learners made more errors when responding to incongruent than congruent items. In terms of RQ2 on L1 activation, ESL learners’ processing speed but not accuracy was affected by the L1 frequencies of component words in the L2 collocations. Further, the RT data showed no significant interaction between condition (congruent vs. incongruent) and L1 word frequencies, suggesting that L1 was activated in the processing of both congruent and incongruent collocations. As for the moderating variables on the congruency effect (RQ3), the interaction between L2 collocation frequency and congruency did not survive model selection, suggesting that ESL learners were sensitive to frequency regardless of congruency and that, more importantly, the congruency effect in accuracy or the lack of it in RT remained regardless of collocation frequency. ESL learners’ reaction to congruency in L2 collocational processing was affected by their length of residence in the US. Longer residence in the US was associated with faster and more accurate processing of incongruent items (see Figure 1). Age of arrival in the country or percentage of daily L2 use did not moderate the congruency effect. The lack of age effect may be attributed to the fact that most ESL participants arrived in the US after age 18 (DeKeyser, Reference DeKeyser2000; DeKeyser et al., Reference DeKeyser, Alfi-Shabtay and Ravid2010). For the null effect of L2 use, one explanation could be that percentage of L2 use did not reflect the quality of L2 use, which may contribute to language development more than quantity (Baker-Smemoe et al., Reference Baker-Smemoe, Dewey, Bown and Martinsen2014).

Table 2. Descriptive statistics for ESL learners’ RT and accuracy

Table 3. Mixed-effects model for ESL learners’ RT

*p < 0.5; **p < .01; ***p < .001

Table 4. Mixed-effects model for ESL learners’ accuracy

*p < 0.5; **p < .01; ***p < .001

Figure 1. Interactions in ESL learners’ RT and accuracy.

Participants

Thirty-three EFL learners were recruited. They were non-English majors in their sophomore or junior years in college in mainland China, with an average age of 19.52 years (SD = 0.94, range = 18–22). They had never lived or studied in an English-speaking country and had received English instruction for an average of 10.39 years (SD = 2.36, range = 6–15). Self-reported CET4 scores were used as a proxy of EFL learners’ proficiency level. All but four participants had taken the test, and those who did took the test less than 2 years ago from the time of data collection. The CET4 has a maximum score of 710, and the average score of the EFL participants was 494.97 (SD = 57.59, range = 372–593). According to China’s National Education Examinations Authority (n.d.), the participants’ mean score was around the 44th percentile, with a range from the 4th to 90th percentile. The EFL learners’ CET scores suggested that they were of intermediate-low to intermediate proficiency.

Analysis

Mixed-effects models were built to analyze RT and accuracy data. The RT trimming and transformation, data coding, modeling procedure, model comparison, and model criticism followed those in Experiment 1. RT trimming affected 2.50% of the EFL data. The initial maximal models for RT and accuracy included (1) main effects of theoretical interest: L2 collocation frequency, condition (congruent and incongruent), L1 Word1 and Word2 frequencies, L2 proficiency (CET4 scores), and length of instruction; (2) interactions between the main effects of interest; (3) covariates: collocation length (number of letters), L2 Word1 and Word2 frequencies, and MI; (4) maximal random-effects structure justified by the data (Barr et al., Reference Barr, Levy, Scheepers and Tily2013). Four EFL participants were excluded from analysis due to missing CET4 scores.

Results and discussion

Table 5 presents the descriptive statistics for EFL learners’ RT and accuracy. Mixed-effects models (see Tables 6 and 7) showed that unlike ESL learners, EFL learners showed a congruency effect in both processing speed and accuracy (RQ1), reacting significantly faster and more accurately to congruent than incongruent items. Similar to ESL learners, EFL learners were affected by the L1 frequencies of component words only in RT but not in accuracy (RQ2). L1 word frequencies did not interact with condition, an indication of L1 activation in both congruent and incongruent collocation processing. The interaction between L1 Word1 frequency and length of instruction showed a trend toward significance. This interaction suggested that L1 Word1 frequency effect would be slightly larger for learners with longer length of instruction.

Table 5. Descriptive statistics for EFL learners’ RT and accuracy

Table 6. Mixed-effects model for EFL learners’ RT

*p < 0.5; **p < .01; ***p < .001

Table 7. Mixed-effects model for EFL learners’ RT

*p < 0.5; **p < .01; ***p < .001

In terms of variables that moderated the congruency effect (RQ3), there was no significant interaction between L2 collocation frequency and congruency, indicating that EFL learners showed a congruency effect even for high-frequency collocations. Length of instruction did not interact with congruency, meaning that more classroom instruction did not reduce L1 influence in EFL learners’ collocational processing. The RT data showed that L2 proficiency did not moderate congruency. This is in line with Wolter and Gyllstad (Reference Wolter and Gyllstad2013) and Wolter and Yamashita (Reference Wolter and Yamashita2018), which revealed null results of L2 proficiency, but stands in contrast with Sonbul and El-Dakhs (Reference Sonbul and El-Dakhs2020), who found that advanced learners showed a smaller congruency effect. As mentioned in the literature review, Sonbul and El-Dakhs (Reference Sonbul and El-Dakhs2020) attributed the null results in Wolter and Gyllstad (Reference Wolter and Gyllstad2013) and Wolter and Yamashita (Reference Wolter and Yamashita2018) to the treating of L2 proficiency as a categorical variable and to including participants of a limited range of proficiency levels. In the current study, even when L2 proficiency was analyzed as a continuous variable and the range of proficiency was fairly wide (i.e., from 4th to 90th percentile), L2 proficiency did not come out as a significant moderating variable of congruency. In the accuracy analysis, L2 proficiency interacted with L2 collocational frequency. It seems that EFL learners with higher proficiency level benefitted more from greater collocational frequency. Proficiency interacted with congruency in an unexpected direction such that the higher the L2 proficiency, the more errors EFL learners made when responding to incongruent collocations. Although such results seemed counterintuitive, one speculation was that EFL learners of lower proficiency lacked confidence in their ability and tended to think that items they did not know were not necessarily unacceptable. Thus, even when these lower level learners did not know the incongruent items, they accepted the items as collocations, leading to higher accuracy. If this was the case, lower level learners should also have made more errors for noncollocational control items, thinking that those items were collocations that they have not learned. In contrast, learners of higher proficiency would be more certain and reject items that they were not familiar with—namely, incongruent collocations as well as noncollocates. To evaluate this explanation, a follow-up analysis on the relationship between proficiency and accuracy for noncollocational control items was conducted. Proficiency turned out to be significantly and positively related to accuracy for noncollocational control items (z = 4.60, p < .001; see Appendix D for the full model), suggesting that EFL learners with lower proficiency were indeed more likely to accept a control item as a collocation. The lack of proficiency and congruency interaction in the RT analysis, which only involved correct responses, also supported this explanation: Once the EFL learners have learned the collocations, proficiency had little influence on the learners’ processing of congruent and incongruent collocations.

The underlying mechanism of the congruency effect

To reiterate, two explanations have been proposed in the literature to account for the congruency effect—namely, L1 activation and order of acquisition. The results of the current study favor L1 activation for two reasons. First, the absence of a congruency effect in ESL learners contradicts the proposal that the congruency effect comes from earlier acquisition of congruent items. If it is the case that congruent items are processed faster because they are learned earlier, they are likely to always enjoy an advantage over their incongruent counterparts regardless of whether a learner has lived in the L2 environment. Second, the effect of L1 lexical frequency on L2 collocational processing constitutes direct evidence for L1 activation.Footnote ¹ That is, the higher the L1 lexical frequencies of individual words in the L2 collocations, the faster L2 learners processed the collocations. More importantly, L1 was activated for both congruent and incongruent collocations and for EFL as well as ESL learners even when ESL learners did not show a congruency effect in RT. These findings indicate that, consistent with Conklin and Carrol’s (Reference Conklin, Carrol, Siyanova-Chanturia and Pellicer-Sánchez2018) hypothesis, L1 translation equivalents of words in the L2 collocations are automatically activated. It is not known, however, what routes learners may take after the activation of L1 translation equivalents to access the concepts of the L2 collocations. Based on Conklin and Carrol (Reference Conklin, Carrol, Siyanova-Chanturia and Pellicer-Sánchez2018) and Jiang (Reference Jiang2000), I propose some possible scenarios in the following paragraphs that could account for the presence of the congruency effect among EFL learners and the absence of it among ESL learners.

For incongruent collocations, it is most likely that after activation of the L1 translation equivalents of individual words, L2 learners need to suppress their L1 because the activated L1 translation equivalents do not constitute felicitous L1 expressions. L2 learners then switch to the L2 route, which involves the activation of L2 collocations to directly access the concepts. The processing speed for incongruent collocations, therefore, depends on the strength of the conceptual link between an L2 collocation and its meaning and/or how good L2 learners are at suppressing their L1. EFL learners may have a comparatively weak conceptual link and/or a more dominant L1 that is harder to suppress. ESL learners, in comparison, may have established a stronger link between L2 collocations and concepts, or their L1 might be inhibited by the L2 immersive environment (Linck et al., Reference Linck, Kroll and Sunderman2009).

For congruent collocations, there are three possible scenarios. The first one entails dual activation, where the activated L1 translation equivalents lead to the activation of the corresponding L1 collocation as well as the L2 collocation. The dual activation may explain EFL learners’ faster processing of congruent collocations over incongruent ones (Wolter & Gyllstad, Reference Wolter and Gyllstad2011). Such a route, however, seems less plausible for ESL learners, who did not show a congruency effect. In the second scenario, the L1 translation equivalents activate the L1 collocation, through which meaning is accessed. For ESL learners, strong representations have been established for L2 collocations, and thus there is little difference in speed between the L2 route for incongruent collocations and the L1-mediated route for congruent ones. EFL learners may also take this route. But because their L2 representations are still weak, the L2 route may be slower than the L1-mediated route, resulting in the congruency effect. Finally, in the third scenario, for ESL learners, it is possible that after the automatic activation of L1 translation equivalents of the individual words, the L2 collocation and its concept are directly activated, without the mediation of the L1 corresponding collocation. The strength of the conceptual links for both congruent and incongruent collocations is similar, and thus there was no congruency effect. This route, which does not involve activation of L1 collocations, may account for the lack of L1 collocation frequency effect in Wolter and Gyllstad (Reference Wolter and Gyllstad2013).

Language experiences, proficiency, and L1 influence

The congruency effect is an indication of the amount of L1 influence in L2 processing. Analyzing learners in two different learning contexts (ESL and EFL) and the moderating variables on the congruency effect (i.e., L2 collocation frequency, length of residence, age of arrival, and length of instruction) informs us about how language experiences may affect L1 influence. Frequency indicates the more specific micro-L2 experiences that learners have with individual linguistic units (Spätgens & Schoonen, Reference Spätgens, Schoonen and Webb2019). Learning context and related variables (length of residence, age of arrival, and length of instruction) represent the macro aspect of one’s L2 experiences—that is, time being immersed in the L2 environment or learning in a classroom setting.

For the micro aspect of experiences, the results for both RT and accuracy showed that regardless of learning context, ESL and EFL learners were tuned to L2 collocation frequency, a finding consistent with usage-based approaches to language acquisition that learning is driven by experiences (e.g., Bybee, Reference Bybee2006). More importantly, the effect of L2 collocation frequency did not interact with congruency, a result similar to that of Wolter and Gyllstad (Reference Wolter and Gyllstad2013). That is, the congruency effect existed for both high- and low-frequency collocations in EFL learners’ RTs and accuracy and ESL learners’ accuracy. This suggested that although repeated encounters can contribute to fluent and accurate processing of collocations, it does not seem to reduce the influence of the L1.

Learning context, the macro aspect of L2 experiences, on the other hand, affects the amount of L1 influence in L2 processing. ESL learners, different from EFL learners, did not show a congruency effect in terms of processing speed. This finding is in line with Yamashita and Jiang (Reference Yamashita and Jiang2010), who attributed the discrepancy between ESL and EFL learners to their different degrees of dependence on the L1 lexicon as a result of learning context difference: When an L2 collocation is first learned, it is linked to its L1 counterpart, which serves as a mediation to meaning, and this dependence on L1 gradually subsides with more L2 exposure, leading to the lack of congruency effect in ESL learners’ RTs. The effects of length of residence on ESL learners’ collocational processing further support the role of learning context in reducing L1 influence. ESL learners’ processing of incongruent collocations was faster with longer length of residence in the US. For processing accuracy, though ESL learners still showed a congruency effect, the longer they lived in the L2 environment, the smaller the congruency effect was. This implies that immersing in an L2 environment alleviates the negative effect of L1-L2 incongruency, making it less difficult to learn and accept L2 collocations that did not have counterparts in the L1. In contrast, for EFL learners in a classroom setting, having more language instruction or being higher in language proficiency did not seem to reduce L1 influence in L2 collocational processing in terms of either speed or accuracy.

The differential effects of L2 collocation frequency, learning context and its related variables (i.e., length of residence, age of arrival, and length of instruction), and L2 proficiency on L1 influence suggest that frequent inhibition of the L1 may be the key to reducing L1 influence. Linck et al. (Reference Linck, Kroll and Sunderman2009) showed that when learners were immersed in the L2 environment, L1 access was constantly suppressed, leading to attenuated L1 influence. In the current study, EFL learners may have encountered an L2 collocation repeatedly, had substantial classroom instruction, and achieved relatively high proficiency, but they were still in an L1 environment with active use of the L1. In contrast, ESL learners not only used the L1 less but also had to suppress the L1 when they used the L2. Reduced access to and frequent inhibition of the L1 may have resulted in lower level of L1 activation, which allowed the ESL learners to become more independent of the L1 in L2 collocational processing. This explanation also provides support for the argument in the previous discussion section that the processing of incongruent collocations depends on how well L2 learners are at L1 suppression.

Limitations

The findings of the study should be interpreted in light of several limitations. First, the L2 proficiency levels of ESL and EFL learners were not matched. The potential differences in proficiency levels between the two groups made it hard to attribute their processing differences solely to the learning context. Although it was found that L2 proficiency did not reduce the congruency effect, we still cannot rule out the possibility that the lack of congruency effect in ESL learners was a result of immersion and higher L2 proficiency combined. However, L2 proficiency and learning context are two constructs that are challenging to disentangle. Immersion might improve L2 proficiency in ways such as enhancing processing efficiency, which may not be captured solely by standardized tests. In fact, in Jiang et al. (Reference Jiang, Li and Guo2020), length of immersion was used as a proxy of L2 proficiency. When matching the proficiency levels of ESL and EFL learners, future studies can use both standardized tests and RT-based measures to provide more comprehensive proficiency profiles of their participants.

The second limitation is related to participants’ familiarity with constituent words in the collocations. Participants’ not knowing the constituent words may have changed the nature of “No” responses in the AJT: Participants indicated that an item was not a collocation because they didn’t know some of the constituent words, not because they thought that the item was a noncollocate. Although the constituent words were estimated to be known to participants based on their proficiency level, future studies should directly check participants’ knowledge of the words in an exit questionnaire.

Another limitation of the study concerns the accuracy of information about learners’ L2 use. ESL participants’ understanding of language use may have varied, with some only considering speaking the language as language use for example. The use of percentage as the unit of L2 use may have further contributed to variations in responses. Definitions of L2 use should be provided and L2 use should be measured in hours in future studies to obtain more accurate information.

Finally, as Yamashita (Reference Yamashita2018) pointed out, the semantic transparency effect may be involved in the congruency effect: Congruent collocations used in previous studies tended to be more transparent than incongruent collocations, and transparent collocations were processed faster (e.g., Gyllstad & Wolter, Reference Gyllstad and Wolter2016). Although the manipulation check showed that L1 English speakers processed congruent and incongruent collocations used in the current study in a similar manner, indicating that these two types of collocations were comparable in transparency, future studies should still obtain semantic transparency ratings of items to reduce the potential confounding effect of transparency.