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Language Switching and Language Mixing

Our results revealed that switching and mixing induced very similar activity in the brain.

By directly comparing switching with mixing, we found that switching activated the IFG (BA45), whereas mixing induced both the left IFG (BA45 and BA47) and left STG (BA22).

The activation of the left IFG in both switching and mixing was expected since this brain region was found to be involved in selecting and integrating semantic relevant

information (Sakai, 2005) and was observed to be in positive correlation with semantic task demands (Raichle et al., 1994; Demb et al., 1995l; Just et al., 1996). Language switching and

mixing sentences imposed higher task demands or increased difficulty compared to non-switch/mixed conditions due to the increased sentence complexity in a switched-mixed sentence relative to non-switch/mixed sentences. Thus, the underlying cognitive process which subserved the amount of activated neural activity in left IFG indicates a dependency on the complexity of sentences in language switching and mixing.

Green (1998) and Price et al. (1999) suggested that the ability to alter between languages were regulated by one’s proficiency level. Increased activation in left IFG was shown to be related to the L2 proficiency in semantic of bilinguals (Perani et al., 1998; Chee et al., 2001;

Perani and Abutalebi, 2005; Tatsuno and Sakai, 2005; Stein et al., 2006, 2009). Although our participants have high proficiency in both languages, the degree of dominance still differs (see Figure 7 for the language effect). It is thus possible that they all acquired the ability to transfer and incorporate the common structures from these two languages, but such

transformation or incorporating is more difficult in switching or mixing sentences than non-switched/mixed ones. Besides that, the activation of the prefrontal activity (IFG) might be caused by the incorporation of an explicit metalinguistic task in our experiment, where individuals were requested to remember the presented auditory sentences. Such task demands could have recruited executive control over access to memory representations in order to assist the comprehension of the language switching and mixing sentences (Thompson-Schill et al., 1997; Fletcher et al., 1998; Dapretto & Bookheimer, 1999). As a consequence, the

implication of the executive control system in language switching and mixing might be a task effect of our study.

It should be noted that numerous neuroimaging studies have greatly expanded our understanding of subcortical-cortical networks in language switching (Graybiel, 1997;

Botvinick et al., 1999; Duncan & Owen, 2000; Middleton & Strick, 2000; Botvinick et al., 2001; Braver et al., 2001; Bunge et al., 2002; Kerns et al., 2004; McCormick et al., 2006).

Abutalebi & Green (2007) also reported a widespread network for bilingual language

production, including prefrontal cortex, inferior parietal lobule, anterior cingulate cortex and basal ganglia. However, we did not find subcortical activities in our experiment. It is

plausible that the use of a listening paradigm might keep the subcortical area silent because the subject did not have to actively inhibit the non-target language and select the target language, as in experiments using a production paradigm. Future study directly comparing producing and comprehending switched/mixed sentences might help unveil the reason for such differences.

In addition to the IFG, we also expected the activation of STG in switching and mixing.

According to Table 7, the highest acquired activation in both switching and mixing

conditions is the left STG (BA22). The STG was found to be located in the Wernicke’s area, an area that is related to speech perception (Wernicke, 1874). Pathological neuroimaging studies have also shown involvement of superior temporal areas in speech perception (Scott

et al., 2000; Hickok & Poeppel, 2000, 2004; Wise et al., 2001; Narain et al., 2003; Scott &

Wise, 2004). Besides that, STG is also shown to be involved in auditory word recognition (Ahmad et al., 2003; Scarabino et al., 2017). The activation of this area in our study is thus compatible with the use of the experimental task as we used a receptive language paradigm (the auditory comprehension). In other words, when participants heard the auditory stimuli, they started to process the auditory information, which led to the activation of the left STG.

Furthermore, Leff et al. (2009) discovered that the left STG was found to mediate the

capacity of auditory short-term memory and the speech comprehension ability (Crinion et al., 2003; Capek et al., 2004; Amici et al., 2007; Friederici et al., 2009). To be specific, when the switching and mixing auditory stimuli were perceived by participants, they had to soon activate the left STG region because they had to understand and also remembered the stimuli due to the task requirement.

The involvement of the right hemisphere, especially the right STG, was also observed in the switching and mixing conditions. Lebrun (1990) discovered that the right hemisphere was responsible for switching and mixing phenomena. Moreover, Martin et al. (1994) found that lesion in the right temporal lobe leads to the pathological switching conditions. Thus, our study supported these two studies and verified that the right STG is involved in language switching and mixing. But what could the function of the right STG be in language switching and mixing? It was proposed that right STG could help discriminate and identify the acoustic

features (Buchanan et al., 2000; Mitchell et al., 2003; Wildgruber et al., 2004; Wildgruber et al., 2005). Therefore, it is plausible that the participants recruited the right STG to better discriminate the sounds of the unexpected switched/mixed word in the auditory recordings to facilitate comprehension.

Taken together, our results supported Abutalebi et al. (2007) finding that auditory language switching task activated inferior prefrontal and superior temporal cortex bilaterally.

In fact, our results extended their finding and revealed that the activation in these regions was not only engaged specifically in the switching conditions but also in the mixing conditions. It is plausible that similar underlying mechanisms were used when producing and/or perceiving mixing/switching sentences.

On the other hand, our finding was not in line with Fabbro's (2000, 2001a, 2001b) studies in pathological switching and mixing, which claimed that language switching relied on the pragmatic system while the linguistic factors are mainly involved in language mixing sentences. We suspected that this could result from the production vs. comprehension difference in the use of experimental tasks.

5.2 Switching and Mixing Direction

We included switching and mixing in both directions (Mandarin to English or the other way around), so we could examine the effect of direction in our experiment. Before exploring into it, we would like to first explain how we calculated switch costs in our study.

In terms of the calculation of switch costs in previous literature, there are two main comparisons that can be applied: one is to change the language of the preceding word while keeping the target word in the same languages (i.e. L2-L1 vs L1-L1) (Meuter & Allport, 1999; Proverbio et al., 2004); the other is to manipulate the target word while maintaining similar sentence context (i.e. L2-L1 vs. L2-L2) (Moreno et al., 2002; Ng et al., 2014; Van Der Meij et al., 2011). For the current study, we adopted the 2nd approach since it allowed us to investigate the effects exerted on different languages of target words in identical sentence context (Liao & Chan, 2016).

We did not find any activity in the EM vs. EE comparison, but found activity in the left dorsolateral prefrontal cortex (DLPFC, BA46) and left ventrolateral prefrontal cortex

(VLPFC, BA47) in the ME vs. MM comparison (see Table 10). The DLPFC has been known for its executive involvement in task switching (Smith & Jonides, 1999; DiGirolamo et al., 2001; Liston et al., 2006) and language switching (Hernandez et al., 2000; Hernandez et al., 2001; Holtzheimer et al., 2005; Kovelman et al., 2008). Specifically, BA46 was suggested to be involved in the regulation of working memory (Leung et al., 2002; Pochon et al., 2002)

and semantic information retrieval (Demb et al., 1995; Kapur et al., 1996; Blumenfeld &

Ranganath, 2007). The VLPFC (BA47) has been implicated in language functions, such as semantic processing (Wong et al., 2002; Chou et al., 2006; De Carli et al., 2007), semantic encoding (Demb et al., 1995; Li et al., 2000) and semantic retrieval (Desmond et al., 1995;

Zhang et al., 2004; Lehtonen et al., 2005).Therefore, the higher activation in the left DLPFC and VLPFC in the mixing ME condition might indicate that switching into a non-dominant language demanded more effort (Poldrack et al., 1999; Wagner et al., 2001; Bookheimer, 2002; Badre et al., 2005; Badre & Wagner, 2007), probably due to more demanding semantic processing/encoding/retrieval and due to controlling and inhibiting the non-target language.

In addition to the DLPFC and VLPFC activation, through the inspection of the cluster-size (KE) in the language switching directions (refer to Table 9), we also observed that the total volume in the ME vs. MM comparison attained higher total volume (KE = 306) when compared to the EM vs. EE comparison (KE = 93). In other words, it seems that switching from a more dominant language (Mandarin) to the non-dominant language (English) would elicit higher activation but not the other way around.

Our findings agreed with an ERP experiment by Liao and Chan (2016). The authors found out that switching (an umbrella term also refers to as language mixing in the current study) from a more dominant (Mandarin) to a non-dominant (Taiwanese) language required extra effort than switching in the other direction, as reflected by the PMN (detection of an

unexpected sound), the N400 (indication of lexical access difficulty) and the frontal negativity (inhibition of the pre-activated representations).

Our results (Tables 9 and 10) supported the well-known BIA+ model (Dijkstra & Van Heuven, 2002; van Heuven & Dijkstra, 2010), which proposed that switching from a more dominant language to a weaker language would be more difficult and demand more cognitive efforts since the lower resting level of the non-dominant language will exert more effort. On the other hand, our results did not support the IC model, which stressed that stronger efforts were required to inhibit the lemma activation attained by the dominant language and thus switching from non-dominant language to dominant one will consume more energy (Green, 1998). Therefore, taken together with previously reviewed studies (Proverbio et al., 2004;

Abutalebi et al., 2007; Wang et al., 2007; Liao & Chan, 2016), our results supported the BIA+ model in language comprehension.

5.3 General Discussion

The current study aimed to answer two questions: (1) Can language switching and mixing be distinguished at the biological level? And (2) does the direction of language

switching or mixing (L1 to L2 or L2 to L1) create any differences in processing cost? Our results showed that switching and mixing in language comprehension activated very similar brain regions, which was drastically different from their clear distinction in language

production in patient research. Similarly, the finding of similar brain activations in language

switching and mixing, suggesting that the use of similar underlying brain mechanisms, are more inclined towards the sociolinguistics views on treating both of them as identical language phenomena and thus disagree with the needs to distinguish them (Hatch, 1976;

Gumperz, 1982; Pakir, 1989; Tay, 1989). Lastly, we found out that processing cost differs in terms of switching/mixing direction: switching/mixing from a more dominant to a less dominant language induced more processing cost than switching/mixing from the other way around.

References

Abutalebi, J., Brambati, S. M., Annoni, J.-M., Moro, A., Cappa, S. F., & Perani, D. (2007).

The neural cost of the auditory perception of language switches: An event-related functional magnetic resonance imaging study in bilinguals. The Journal of

neuroscience, 27(50), 13762-13769.

Abutalebi, J., & Green, D. (2007). Bilingual language production: The neurocognition of language representation and control. Journal of Neurolinguistics, 20(3), 242-275.

Abutalebi, J., & Green, D. W. (2008). Control mechanisms in bilingual language production:

Neural evidence from language switching studies. Language and cognitive processes, 23(4), 557-582.

Abutalebi, J., Miozzo, A., & Cappa, S. F. (2000). Do subcortical structures control ‘language selection’in polyglots? Evidence from pathological language mixing. Neurocase, 6(1), 51-56.

Adrover-Roig, D., Galparsoro-Izagirre, N., Marcotte, K., Ferré, P., Wilson, M. A., & Inés Ansaldo, A. (2011). Impaired L1 and executive control after left basal ganglia damage in a bilingual Basque–Spanish person with aphasia. Clinical linguistics & phonetics, 25(6-7), 480-498.

Aglioti, S., Beltramello, A., Girardi, F., & Fabbro, F. (1996). Neurolinguistic and follow-up study of an unusual pattern of recovery from bilingual subcortical aphasia. Brain,

119(5), 1551-1564.

Aglioti, S., & Fabbro, F. (1993). Paradoxical selective recovery in a bilingual aphasic following subcortical lesions. Neuroreport, 4(12), 1359-1362.

Aglioti, S., Smania, N., Barbieri, C., & Corbetta, M. (1997). Influence of stimulus salience and attentional demands on visual search patterns in hemispatial neglect. Brain and cognition, 34(3), 388-403.

Alexander, G. E., & Crutcher, M. D. (1990). Functional architecture of basal ganglia circuits:

neural substrates of parallel processing. Trends Neurosci, 13(7), 266-271.

Alvarez, R. P., Holcomb, P. J., & Grainger, J. (2003). Accessing word meaning in two

languages: An event-related brain potential study of beginning bilinguals. Brain Lang, 87(2), 290-304.

Ansaldo, A. I., Marcotte, K., Scherer, L., & Raboyeau, G. (2008). Language therapy and bilingual aphasia: Clinical implications of psycholinguistic and neuroimaging research. Journal of Neurolinguistics, 21(6), 539-557.

Ardal, S., Donald, M. W., Meuter, R., Muldrew, S., & Luce, M. (1990). Brain responses to semantic incongruity in bilinguals. Brain Lang, 39(2), 187-205.

Badre, D., Poldrack, R. A., Paré-Blagoev, E. J., Insler, R. Z., & Wagner, A. D. (2005).

Dissociable controlled retrieval and generalized selection mechanisms in ventrolateral prefrontal cortex. Neuron, 47(6), 907-918.

Badre, D., & Wagner, A. D. (2007). Left ventrolateral prefrontal cortex and the cognitive control of memory. Neuropsychologia, 45(13), 2883-2901.

Bedny, M., Caramazza, A., Grossman, E., Pascual-Leone, A., & Saxe, R. (2008). Concepts are more than percepts: the case of action verbs. The Journal of neuroscience, 28(44), 11347-11353.

Bhat, S., & Chengappa, S. (2003). Code Switching in Normal and Aphasic Kannada-English Bilinguals.

Bhat, S., & Shyamala, K. (2005). Code-switching in Normal Hindi-English Bilinguals. Indian Linguistics, 66(1-4), 19-30.

Bialystok, E., Craik, F. I., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459-464.

doi:10.1016/j.neuropsychologia.2006.10.009

Blumenfeld, R. S., & Ranganath, C. (2007). Prefrontal cortex and long-term memory

encoding: an integrative review of findings from neuropsychology and neuroimaging.

The Neuroscientist, 13(3), 280-291.

Bokamba, E. G. (1989). Are there syntactic constraints on code‐mixing? World Englishes, 8(3), 277-292.

Bookheimer, S. (2002). Functional MRI of language: new approaches to understanding the cortical organization of semantic processing. Annual review of neuroscience, 25(1),

151-188.

Botvinick, M., Braver, T. S., Barch, D. M., Carter, C. S., & Cohen, J. D. (2001). Conflict monitoring and cognitive control. Psychological review, 108(3), 624.

Botvinick, M., Nystrom, L. E., Fissell, K., Carter, C. S., & Cohen, J. D. (1999). Conflict monitoring versus selection-for-action in anterior cingulate cortex. Nature, 402(6758), 179-181.

Braver, T. S., Barch, D. M., Gray, J. R., Molfese, D. L., & Snyder, A. (2001). Anterior cingulate cortex and response conflict: effects of frequency, inhibition and errors.

Cerebral Cortex, 11(9), 825-836.

Broersma, M. (2009). Triggered codeswitching between cognate languages. Bilingualism:

Language and Cognition, 12(04), 447-462.

Broersma, M. (2011). Triggered code-switching: Evidence from picture naming experiments.

Modeling bilingualism: From structure to chaos: In honor of Kees de Bot, 37-58.

Broersma, M., & De Bot, K. (2006). Triggered codeswitching: A corpus-based evaluation of the original triggering hypothesis and a new alternative. Bilingualism: Language and Cognition, 9(01), 1-13.

Broersma, M., Isurin, L., Bultena, S., & De Bot, C. (2009). Triggered code-switching:

Evidence from Dutch-English and Russian-English bilinguals.

Bultena, S., Dijkstra, T., & Van Hell, J. (2012). Co-activation of nouns and verbs within and

between languages. Language and cognitive processes, 28(9), 1350-1377.

Bunge, S. A., Hazeltine, E., Scanlon, M. D., Rosen, A. C., & Gabrieli, J. (2002). Dissociable contributions of prefrontal and parietal cortices to response selection. Neuroimage, 17(3), 1562-1571.

Chee, M. W., Soon, C. S., & Lee, H. L. (2003). Common and segregated neuronal networks for different languages revealed using functional magnetic resonance adaptation.

Journal of Cognitive Neuroscience, 15(1), 85-97.

Chou, T. L., Booth, J. R., Bitan, T., Burman, D. D., Bigio, J. D., Cone, N. E., Cao, F. (2006).

Developmental and skill effects on the neural correlates of semantic processing to visually presented words. Human brain mapping, 27(11), 915-924.

Clyne, M. G. (2003). Dynamics of language contact: English and immigrant languages:

Cambridge University Press.

Clyne, M. G., & Moser, H. (1967). Transference and triggering: Nijhoff.

Crinion, J., Turner, R., Grogan, A., Hanakawa, T., Noppeney, U., Devlin, J. T., Stockton, K.

(2006). Language control in the bilingual brain. Science, 312(5779), 1537-1540.

Crosson, B. (1999). Subcortical mechanisms in language: Lexical–semantic mechanisms and the thalamus. Brain and cognition, 40(2), 414-438.

Damasio, A. R., & Tranel, D. (1993). Nouns and verbs are retrieved with differently distributed neural systems. Proceedings of the National Academy of Sciences of the

United States of America, 90(11), 4957-4960.

Daniele, A., Giustolisi, L., Silveri, M. C., Colosimo, C., & Gainotti, G. (1994). Evidence for a possible neuroanatomical basis for lexical processing of nouns and verbs.

Neuropsychologia, 32(11), 1325-1341. doi:10.1016/0028-3932(94)00066-2

De Carli, D., Garreffa, G., Colonnese, C., Giulietti, G., Labruna, L., Briselli, E., Maraviglia, B. (2007). Identification of activated regions during a language task. Magnetic resonance imaging, 25(6), 933-938.

De Vreese, L. P., Motta, M., & Toschi, A. (1988). Compulsive and paradoxical translation behaviour in a case of presenile dementia of the Alzheimer type. Journal of Neurolinguistics, 3(2), 233-259.

Demb, J. B., Desmond, J. E., Wagner, A. D., Vaidya, C. J., Glover, G. H., & Gabrieli, J.

(1995). Semantic encoding and retrieval in the left inferior prefrontal cortex: a functional MRI study of task difficulty and process specificity. Journal of Neuroscience, 15(9), 5870-5878.

Desmond, J. E., Sum, J., Wagner, A., Demb, J., Shear, P., Glover, G., Morrell, M. (1995).

Functional MRI measurement of language lateralization in Wada-tested patients.

Brain, 118(6), 1411-1419.

DiGirolamo, G. J., Kramer, A. F., Barad, V., Cepeda, N. J., Weissman, D. H., Milham, M. P., Webb, A. (2001). General and task-specific frontal lobe recruitment in older adults

during executive processes: a fMRI investigation of task-switching. Neuroreport, 12(9), 2065-2071.

Dijkstra, T., & Van Heuven, W. J. (2002). The architecture of the bilingual word recognition system: From identification to decision. Bilingualism: Language and Cognition, 5(03), 175-197.

Duncan, J., & Owen, A. M. (2000). Common regions of the human frontal lobe recruited by diverse cognitive demands. Trends Neurosci, 23(10), 475-483.

Fabbro, F. (1999). The neurolinguistics of bilingualism: An introduction.

Fabbro, F. (2001a). The bilingual brain: bilingual aphasia. Brain Lang, 79(2), 201-210.

doi:10.1006/brln.2001.2480

Fabbro, F. (2001b). The bilingual brain: cerebral representation of languages. Brain Lang, 79(2), 211-222. doi:10.1006/brln.2001.2481

Fabbro, F., & Daro, V. (1995a). Delayed auditory feedback in polyglot simultaneous interpreters. Brain Lang, 48(3), 309-319. doi:10.1006/brln.1995.1013

Fabbro, F., & Paradis, M. (1995b). Differential impairments in four multilingual patients with subcortical lesions. Aspects of bilingual aphasia, 3, 139-176.

Fabbro, F., Peru, A., & Skrap, M. (1997). Language disorders in bilingual patients after thalamic lesions. Journal of Neurolinguistics, 10(4), 347-367.

Fabbro, F., Skrap, M., & Aglioti, S. (2000). Pathological switching between languages after

frontal lesions in a bilingual patient. Journal of Neurology, Neurosurgery &

Psychiatry, 68(5), 650-652.

Graybiel, A. M. (1997). The basal ganglia and cognitive pattern generators. Schizophrenia bulletin, 23(3), 459.

Green, D. W. (1986). Control, activation, and resource: A framework and a model for the control of speech in bilinguals. Brain Lang, 27(2), 210-223.

Green, D. W. (1998). Mental control of the bilingual lexico-semantic system. Bilingualism:

Language and Cognition, 1(02), 67-81.

Green, D. W., & Abutalebi, J. (2013). Language control in bilinguals: The adaptive control hypothesis. J Cogn Psychol (Hove), 25(5), 515-530.

doi:10.1080/20445911.2013.796377

Green, D. W., & Wei, L. (2014). A control process model of code-switching. Language, Cognition and Neuroscience, 29(4), 499-511.

Grosjean, F. (1985). The bilingual as a competent but specific speaker‐hearer. Journal of Multilingual & Multicultural Development, 6(6), 467-477.

Gumperz, J. J. (1982). Discourse strategies (Vol. 1): Cambridge University Press.

Hatch, E. (1976). Studies in language switching and mixing. Language and Man:

Anthropological Issues, 201-214.

Hernandez, A. E. (2009). Language switching in the bilingual brain: What’s next? Brain

Lang, 109(2), 133-140.

Hernandez, A. E., Dapretto, M., Mazziotta, J., & Bookheimer, S. (2001). Language switching and language representation in Spanish–English bilinguals: An fMRI study.

Neuroimage, 14(2), 510-520.

Hernandez, A. E., Martinez, A., & Kohnert, K. (2000). In search of the language switch: An fMRI study of picture naming in Spanish–English bilinguals. Brain Lang, 73(3), 421-431.

Herschmann, H., & Pötzl, O. (1920). Bemerkungen über die Aphasie der Polyglotten.

Zentralblatt Neurologie, 39, 114-128.

Holtzheimer, P., Fawaz, W., Wilson, C., & Avery, D. (2005). Repetitive transcranial magnetic stimulation may induce language switching in bilingual patients. Brain Lang, 94(3), 274-277.

Ide, J. S., & Chiang-shan, R. L. (2011). A cerebellar thalamic cortical circuit for error-related cognitive control. Neuroimage, 54(1), 455-464.

Ijalba, E., Obler, L. K., & Chengappa, S. (2008). 3 Bilingual Aphasia. The handbook of bilingualism, 8, 71.

Jackson, G. M., Swainson, R., Cunnington, R., & Jackson, S. R. (2001). ERP correlates of executive control during repeated language switching. Bilingualism: Language and Cognition, 4(02). doi:10.1017/s1366728901000268

Kachru, B. B. (1978). Toward structuring code-mixing: An Indian perspective. International Journal of the Sociology of Language, 1978(16), 27-46.

Kamwangamalu, N. M. (1992). ‘Mixers’ and ‘mixing’: English across cultures. World Englishes, 11(2‐3), 173-181.

Kapur, S., Tulving, E., Cabeza, R., McIntosh, A. R., Houle, S., & Craik, F. I. (1996). The neural correlates of intentional learning of verbal materials: a PET study in humans.

Cognitive Brain Research, 4(4), 243-249.

Kemmerer, D., Rudrauf, D., Manzel, K., & Tranel, D. (2012). Behavioral patterns and lesion sites associated with impaired processing of lexical and conceptual knowledge of actions. Cortex, 48(7), 826-848. doi:10.1016/j.cortex.2010.11.001

Kerns, J. G., Cohen, J. D., MacDonald, A. W., Cho, R. Y., Stenger, V. A., & Carter, C. S.

(2004). Anterior cingulate conflict monitoring and adjustments in control. Science, 303(5660), 1023-1026.

Kim, A., & Osterhout, L. (2005). The independence of combinatory semantic processing:

Evidence from event-related potentials. Journal of Memory and Language, 52(2), 205-225.

King, J. W., & Kutas, M. (1995). Who did what and when? Using word-and clause-level ERPs to monitor working memory usage in reading. Cognitive Neuroscience, Journal of, 7(3), 376-395.

Kluender, R., & Kutas, M. (1993). Bridging the gap: Evidence from ERPs on the processing of unbounded dependencies. Cognitive Neuroscience, Journal of, 5(2), 196-214.

Kootstra, G. J., Van Hell, J. G., & Dijkstra, T. (2012). Priming of code-switches in sentences:

The role of lexical repetition, cognates, and language proficiency. Bilingualism:

Language and Cognition, 15(04), 797-819.

Kovelman, I., Shalinsky, M. H., Berens, M. S., & Petitto, L.-A. (2008). Shining new light on the brain's “bilingual signature”: a functional Near Infrared Spectroscopy

investigation of semantic processing. Neuroimage, 39(3), 1457-1471.

Kroll, J. F., Bobb, S. C., & Hoshino, N. (2014). Two Languages in Mind Bilingualism as a Tool to Investigate Language, Cognition, and the Brain. Current directions in psychological science, 23(3), 159-163.

Lebrun, Y. (1990). Apraxia of speech: A critical review. Journal of Neurolinguistics, 5(4), 379-406.

Lebrun, Y. (1991). Stuttering and epilepsy. Journal of Neurolinguistics, 6(4), 433-444.

Lehtonen, M. H., Laine, M., Niemi, J., Thomsen, T., Vorobyev, V. A., & Hugdahl, K. (2005).

Lehtonen, M. H., Laine, M., Niemi, J., Thomsen, T., Vorobyev, V. A., & Hugdahl, K. (2005).