Brain activation during idiom processing

Research on brain activation during L1 idiom processing has also made significant progress in recent years, while L2 research in this area has yet to be investigated. One critical line of investigation has been whether the right hemisphere is responsible for figurative language comprehension, including idioms and, for example, metaphors. An early study on metaphor comprehension looked at possible differences in hemispheres by comparing left- and right-brain damaged aphasic patients (Winner & Gardner, 1977). In a picture-metaphor matching task, the authors found that patients with left- hemisphere damage were able to correctly match metaphors to images, while those with right- hemisphere damage were not. Van Lancker and Kempler (1987) conducted a similar task using idioms, and found similar results. Both results suggested that figurative language processing occurs primarily in the right hemisphere (RH), unlike other types of lexical activation. Jung-Beeman (2005) later refined this idea in the Coarse Semantic Coding Theory, which suggests that each hemisphere is divided into fine- and course-coding (left and right hemispheres [LH and RH], respectively). In this case, figurative language, using more distant semantic associations and conceptual relationships than literal language, belongs to the course-coding that may be dominantly located in the right hemisphere. However, recent research has taken issue with the RH theory (e.g., A. M. Rapp, 2013; A. M. Rapp, Leube, Erb, Grodd,

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& Kircher, 2007). Critically, the differences found between patients in Winner and Gardner (1977) may apply more to difficulties with image identification rather than idiom comprehension as both types of patients were able to correctly describe the meaning of the metaphors. Difficulty with images rather than figurative language itself may also be attributed to the right hemisphere, an issue that extends to the idiom study from Van Lancker and Kempler (1987). Furthermore, while course-coding theory may apply straight-forwardly to metaphorical meaning, idioms are associated with very specific, word-like meanings, and may indeed be more representative of long words (Cacciari & Papagno, 2012). Giora (1997) addresses this issue with a further distinction in language between salient (or familiar, fixed expressions, i.e., idioms) and non-salient (unfamiliar non-literal language, i.e., novel metaphors) language. According to this theory, the right hemisphere is primarily responsible for processing only novel non-literal expressions. Thus, not all non-literal language may be RH dominant (see e.g., Cieślicka & Heredia, 2011; A. M. Rapp, 2018).

However, rather than showing clear divisions in hemispheric locality of activation between literal and figurative language, L1 idiom research shows a complex picture of idiom comprehension involving both hemispheres of the brain. Several metanalyses (A. M. Rapp, 2018; A. M. Rapp, Mutschler, & Erb, 2012) have relooked at the body of non-literal language processing studies and determined that results are less lateralized than previously suggested. In the first metanalysis, A. M. Rapp et al. (2012) identified 38 fMRI studies on non-literal language, including 7 idiom studies, and found that of only 33% of the activated foci were in the right hemisphere. In particular, the authors identified the parahyppocampal gyrus, possibly dealing with disambiguation (e.g., Hoenig & Scheef, 2005) and emotional connotation (e.g., Proverbio, Crotti, Zani, & Adorni, 2009); the medial prefrontal cortex, critical in perspective taking and Theory of Mind (e.g., Amodio & Frith, 2006), or suppression of alternative interpretations in idiom comprehension (e.g., Papagno & Romero-Lauro, 2010); the left precentral gyrus, reflecting motor semantics (e.g., Pulvermüller & Fadiga, 2010); the LH thalamus, identifying attributive categories in metaphor comprehension (e.g., Stringaris et al., 2006) or indicating increased cognitive demand (e.g., Saalmann & Kastner, 2011); and the right cerebellum, which may play a role in comprehension (e.g., Cook, Murdoch, Cahill, & Whelan, 2004) but is also an extremely connected area of the brain. In an updated metanalysis, A. M. Rapp (2018) looked at metaphor and idiom comprehension separately, and 11 studies on idioms (and 1 on proverbs) were included. Authors found an equal contribution in the number of loci reported per hemisphere, though the right hemisphere was more spatially distinct. While some of the studies showed distinct patterns when comparing figurative and literal interpretations (e.g., right precuneus, right middle front gyrus, and right posterior middle temporal gyrus in Mashal et al., 2008 and Lauro, Tettamanti, Cappa, & Papagno, 2008), others did not find differences using this contrast (e.g., Kana et al., 2012; Raposo, Moss, Stamatakis, & Tyler, 2009). Overall, these studies suggest that idiom processing is an extremely complex process which

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seems to incorporate many of the skills needed for figurative language processing. Furthermore, native speakers make use of many different parts of the brain in doing so.

There is little research including L2 idiom comprehension and brain activation. However, evidence is available divided visual field research. Cieślicka and Heredia (2011) investigated the hemispheric contributions in L1 and L2 idiom processing using a divided visual field paradigm and lexical priming. Context and salience were in focus for this study as both have been predicted to cause asymmetries in activation between hemispheres. According the Giora’s Graded Salience Hypothesis, the critical distinction separating hemispheric activation and processing mechanisms is not literal vs. figurative language but rather salient vs. non-salient language (e.g., Giora, 1997). Non-salient, rather than non-literal language, may cause more activation in the RH, in line with the Fine-Course Coding Theory (Jung-Beeman, 2005) and may be at the root of the inconsistencies in findings in L1 non-literal language processing studies (e.g.,A. M. Rapp, 2018). Increased RH activation in L2 (non-salient) compared to L1 (salient) idiom processing was predicted following these theories.

Additionally, contextual studies have suggested that the RH is less subject to contextual influence than the LH (e.g., Cieślicka & Heredia, 2011), and only the LH would show differences between figurative and literal interpretations of idioms. The authors did not find significant differences between hemispheres regarding context, but the language being presented did play a role in literal and figurative as well as hemispheric activation. Overall priming effects for literal language were much greater in L2 processing compared to L1 processing, and figurative meanings in the L2 showed more priming in the RH compared to the LH. Increased LH activation of literal meanings in the L2 condition are in line with research by Fogliata et al. (2007) suggesting that these salient meanings require more inhibitory control to suppress competing literal meanings during figurative activation. These results are also in agreement with saliency-based theories in L2 idiom processing research suggesting that literal meanings have a special status in L2 processing (here equated with native language; e.g., Cieślicka, 2006). Notably, in a follow-up study using the same paradigm focusing on idiom decomposability (Cieślicka, 2013a), these hemispheric differences were only partially substantiated. Citron et al. (2020) investigated L1 and L2 processing of metaphors in a recent fMRI study and did not find evidence of hemispheric differences. Instead, their data suggests that L2 readers were less affected by figurativeness than L1 readers during comprehension. With such mixed results, further investigation using idioms and fMRI is necessary to adequately look at this complex topic. To our knowledge, there are no such fMRI studies looking at L1 and L2 idiom comprehension simultaneously to date.

In addition to hemispheric differences in idiom processing based on language, L2 readers face additional challenges for language processing that may be impacted by proficiency. Studies have found increased activation in tasks for L2 compared to L1 processing such as picture naming (e.g., Hernandez & Meschyan, 2006), sentence-reading (e.g., Shirley-Ann Rüschemeyer et al., 2006), listening (e.g.,

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Shirley‐Ann Rüschemeyer et al., 2005), and even mathematical calculations (e.g., Wang, Lin, Kuhl, & Hirsch, 2007). While early accounts of L2 neural organization relied on the idea that different systems are responsible for L1 and L2 language processing and therefore account for such differences, recent studies show evidence that not only do L1 and L2 grammar and neural activations overlap early in acquisition (see e.g., Luk, Green, Abutalebi, & Grady, 2011), but proficiency modulates the similarity of L1 and L2 processing (see e.g., Perani & Abutalebi, 2005). Green, Crinion, and Price (2006) even go so far as to propose that qualitative differences between L1 and L2 processing in neural activation decrease as proficiency increases. This idea is based on evidence of increased effort in production as shown by brain activity in low-proficient L2 participants (e.g., Briellmann et al., 2004; De Bleser et al., 2003) compared to highly-proficient L2 participants, which also applies to comprehension (e.g., Perani et al., 1998). Thus, while the idiom study done by Cieślicka and Heredia (2011) may point to neural differences in idiom processing based on language, these differences may become less pronounced or even disappear with increasing proficiency. Though more research is necessary in order to determine whether these such differences apply to activation of literal and figurative meaning in idiom processing, L2 idiom processing likely presents similarly or even more complex processes than those needed in L1 idiom processing.

7.2 T

In this study, we aimed to answer three questions:

1) Does idiom comprehension differ between native and non-native readers? 2) Does proficiency correlate with activation patterns?

3) Does idiomatic and literal sentence processing differ within and between L1 and L2 readers? Based on the existing body of literature, we predict that regarding Question 1, idiom comprehension will show differences in activation between L1 and L2 readers. We also expect that, if L2 idiom processing becomes more native-like as proficiency increases, activation patterns may show correlations with proficiency in areas of the brain associated with idiom comprehension (see e.g., A. M. Rapp, 2018). Finally, regarding Question 3, we predict that there may be differences in activation based on the figurativeness of the sentence. However, we do not expect these differences to show isolated hemispheric involvement (i.e., right-lateralization for figurative language).