Co-lateralized bilingual mechanisms for reading in single and dual language contexts: evidence from visual half-field processing of action words in proficient bilinguals

Abstract

When reading, proficient bilinguals seem to engage the same cognitive circuits regardless of the language in use. Yet, whether or not such “bilingual” mechanisms would be lateralized in the same way in distinct—single or dual—language contexts is a question for debate. To fill this gap, we tested 18 highly proficient Polish (L1) —English (L2) childhood bilinguals whose task was to read aloud one of the two laterally presented action verbs, one stimulus per visual half field. While in the single-language blocks only L1 or L2 words were shown, in the subsequent mixed-language blocks words from both languages were concurrently displayed. All stimuli were presented for 217 ms followed by masks in which letters were replaced with hash marks. Since in non-simultaneous bilinguals the control of language, skilled actions (including reading), and representations of action concepts are typically left lateralized, the vast majority of our participants showed the expected, significant right visual field advantage for L1 and L2, both for accuracy and response times. The observed effects were nevertheless associated with substantial variability in the strength of the lateralization of the mechanisms involved. Moreover, although it could be predicted that participants' performance should be better in a single-language context, accuracy was significantly higher and response times were significantly shorter in a dual-language context, irrespective of the language tested. Finally, for both accuracy and response times, there were significant positive correlations between the laterality indices (LIs) of both languages independent of the context, with a significantly greater left-sided advantage for L1 vs. L2 in the mixed-language blocks, based on LIs calculated for response times. Thus, despite similar representations of the two languages in the bilingual brain, these results also point to the functional separation of L1 and L2 in the dual-language context.

Functional lateralization of tool-sound and action-word processing in a bilingual brain

“…Consistent with numerous fMRI studies (e.g. Hunter & Brysbaert, 2008) showing that the VHF paradigm is a good measure of cerebral language dominance, our current study demonstrated that, despite some variability, bilinguals have productive language typically lateralized (to the left hemisphere), and in line with the results of our previous study (Krefta et al, 2015) that both languages (L1 and L2) have similar organization in their brains (there is clear co-lateralization). As expected, though, bilinguals showed atypical (hemispherically balanced) organization of processing action-related sounds, that is both in the form of action words as such, and tool sounds (irrespective of the language that they used to identify a given sound).…”

“…On the other hand, there is also evidence that L2 processing can take place in a different cortical network than L1, and that for processing of L2 there is weaker lateralization as compared to L1 (Nelson, Liu, Fiez, & Perfetti, 2009;Huang, Itoh, Kwee, & Nakada, 2012;Park, Badzakova-Trajkov, & Waldie, 2012). Our results for language production (reading words in VHF tests) are thus in line with the first group of reports which suggest a common brain network for L1 and L2, and unambiguously corroborate the existence of the co-lateralization of L1 and L2 in the bilingual brain demonstrated in our previous study (Krefta et al, 2015). This is at variance with reports showing that the processing of L2 is more hemispherically balanced than that of L1.…”

“…All participants were native speakers of Polish (L1) who also declared their late bilingualism (i.e., they started second language learning typically well after the age of 6; see Reifegerste et al, 2019) but high fluency in English (L2). Participants' fluency in L2 was established in three ways: (1) on the basis of their field of study -English Philology and/or Pedagogy in English at Adam Mickiewicz University in Poznan (Poland), and/or (2) the possession of language certificates (e.g., at least Certificate in Advanced English -CAE, typically higher; as in the study by Krefta, Michalowski, Kowalczyk, & Kroliczak, 2015), and/or (3) the requirement of fluent command of English for performing a job in international companies.…”

“…Endnote 1 Hunter and Brysbaert (2008) suggested that in VHF studies the stimuli should not be visible for more than 200 ms. Earlier studies from our laboratory (Klichowski & Kroliczak, 2017;Krefta et al, 2015) have demonstrated that, with the adopted parameters of the procedure and stimulus characteristics, a target duration of 217 ms leads to the required response accuracy of approximately 75% (see also McNair & Harris, 2012;but cf. Helon & Kroliczak, 2014).…”

Unique Neural Characteristics of Atypical Lateralization of Language in Healthy Individuals

“…Of course, when compared to modern English, Polish has some unique features: rich inflectional morphology, grammatical gender, relatively free word order, as well as some differences in phonology to name just a few. Yet, in earlier studies from our laboratory we convincingly demonstrated that the lateralization of single word utterances and processing is quite similar in Polish and English (Krefta et al, 2015 ; Klichowski and Kroliczak, 2017 ).…”