Coexistence of Pathological Switching and Mixing

It is sometimes difficult to have a clear cut distinction between pathological switching and pathological mixing. Therefore, it is plausible to have the coexistence of both pathologies in patients.

The coexistence of pathological switching and mixing might reflect impairment in the executive control and true language deficits, where patients have trouble in constructing phrases/sentences with appropriate syntactic structure or the inability to search for relevant words/vocabulary of a language (Ijalba et al., 2008).

Patients who experienced brain damage may alter their language control and general cognitive capabilities in order to manage dual-language use (Hernandez et al., 2000). In this regard, Fabbro (2000) stated that both pathological switching and mixing might be correlated to the capacity to withdraw attention and resources from L2, where the patients experience inability to focus and extract L2 information from the L2 resources. In addition, pathological switching and mixing might reflect the weakening of the inhibition control of unwanted L2 in cognitive capacity as they are unable to avoid the L2 interference when using the native language.

Moreover, the ability to use one language instead of another by bilinguals and multilinguals are mainly regulated by one’s proficiency level (Green, 1998; Price et al., 1999).

Therefore, when the proficiency of L2 in bilinguals and multilinguals increases, the language users have the ability to transfer the common structures from L2 and incorporate with L1 structures, which is somehow lacked in pathological patients to correctly transfer and inhibit pathological switching and mixing of undesirable target language.

Mariën et al. (2005) reported a case study on a 10 year-old English-Dutch bilingual (EM)

who had two strokes, which caused him to spontaneously switch from L1 to L2 and mix L1 and L2 linguistic units in a conversation, even though he was instructed to use only one language. The first stroke caused him to have disrupted L1 and L2 with poor comprehension and speech construction. He eventually experienced remission of those symptoms after three weeks, and gradually acquired recovery in his L1. However, the second stroke after seven weeks caused his L1 to deteriorate back to the initial state, the oral and comprehension reading for L2 was worse than the first stroke and he even experienced more frequent pathological switching and mixing conditions. After months of treatment, EM’s condition recovered gradually with remission of global aphasia in L1 and L2, and regained his ability to switch and mix languages appropriately. At the early stages of the strokes, computerized tomography (CT), MRI, and single-photon emission computed tomography (SPECT) revealed that the lesions were found in the left frontal cortex, left temporo-parietal areas, left caudate nucleus, and left thalamus. Improved blood flow (perfusion) were found in the left frontal lobe and left caudate nucleus on the later stage when EM recovered from his aphasia and pathological switching and mixing conditions. The parallel remission of frontal lobe and caudate nucleus with the pathological symptoms of language switching and mixing suggested that the anterior loop of the subcortical-cortical circuit (e.g., prefrontal cortex, caudate nucleus, globus pallidus, and the ventral anterior thalamic nucleus) as proposed by Alexander and Crutcher (1990) was proven to be the neural counterpart for the language processing of language switching and mixing.

Thus, the circuit which includes the left frontal lobe and basal ganglia might cause the pathological switching and mixing in EM. In fact, the anterior loop of the subcortical-cortical pathway was found to be involved in a more general process, not just specific to language domain, but associated in multiple domains such as executive, decision-making and attentional cognitive control (Alexander & Crutcher, 1990; Aglioti et al., 1997). It was further supported by studies on multilingual language processing, stating that cortical-subcortical loop is not unique to multilinguals, or specific to language, but crucial for language switching (Paradis &

Goldblum, 1989; Zatorre, 1989; Aglioti et al., 1997; Crosson, 1999).

To conclude Sections 2.2.1-2.2.3, we provide Tables 2, 3 and 4 to summarize neuropsychological and neuroimaging studies about language switching and mixing, respectively.

Table 2: Neuroimaging Studies Investigating Pathological Switching and Pathological Mixing in Bilinguals and Multilinguals

Authors Pathological Switching Pathological Mixing

Herschmann and Pötzl (1920); Pötzl (1925, 1930);

A Leischner (1948)

Parietal lobe

Leischner (1943,1983a) Left superior temporal gyrus

and the left inferior parietal lobe

Stengel and Zelmanowicz (1934); Zatorre (1989)

Frontal lobe

Perecman (1984) left temporal lobe

Aglioti et al. (1993, 1996) Left basal ganglia Lebrun (1991) Right Hemisphere

Martin et al. (1994) Right temporal lobe (epilepsy) Fabbro and Paradis (1995b) Anterior structure of frontal

lobe

-

Fabbro et al. (1997) Left thalamic

Fabbro (2001a) Frontal lobe (left and right) and Left ACC

Left postrolandic and parieto-temporal (left hemisphere)

Abutalebi et al. (2000) Head of the left caudate

nucleus (subcortical) Abutalebi & Green (1986;

2008)

Subcortical (basal ganglia) and frontal lobe

Mariën et. al. (2005) Left frontal lobe and basal ganglia (caudate nucleus) Abutalebi and Green

(2007)

Basal ganglia, ACC, prefrontal cortex Ansaldo et al. (2008) Left basal ganglia

Adrover-Roig et al. (2011) Left basal ganglia

Table 3: Neuroimaging Studies Investigating Language Switching in Bilinguals and Multilinguals

Authors Method Subjects Main Findings

Price et al. (1999) PET study in word naming task

Six late bilinguals (German-English)

Higher activation in supramarginal gyri, and left posterior inferior frontal gyrus (Broca’s area) in switched condition

Increased activation of the dorsolateral prefrontal cortex (DLPFC) for the switched language condition

Jackson et al. (2001) ERP experiment of language switching in a digit naming task

Twenty-six native English (L1) speaker and capable of naming the digits 1 to 8 fluently in a second language (L2)

Higher inhibition is required to suppress the more dominant language (L1). Language switching induced the parietal and frontal activity.

Rodriguez-Fornells

Selective activation of the left anterior prefrontal region (Brodmann areas 45 and 9) presented only in bilinguals Chee et al. (2003) fMRI study of word

Activation in left prefrontal, lateral and inferior temporal regions in mixed-language conditions

Mandarin) compared to the single language (English-only) conditions. Greater cognitive resources in mixed-language conditions.

Urge to speak in their less frequently used language (L2) when left DLPFC is stimulated.

treatment Crinion et al. (2006) PET and fMRI study of

semantic decisions on target words preceded by prime words related or unrelated in meaning and either in the same language or in a different language

PET 11 late German–English bilinguals

fMRI 14 late German–

English bilinguals

fMRI 9 late Japanese–English bilinguals

fMRI 9 late Japanese–English bilinguals

increased activation in left head of caudate for target-primes pairs unrelated in meaning or related in meaning but differing in language

Table 4: Neuroimaging Studies Investigating Language Mixing in Bilinguals and Multilinguals

Authors Method Subjects Main Findings

Moreno et al. (2002) ERP experiment in

comprehending unexpected

Unexpected switching conditions induced the N400, LAN effects (relate to the complexity of syntactic structural processing) and LPC/ P600 (reflect the reanalysis of complicated sentences. The switched condition incur greater processing cost as compared to non-switched condition.

The mixing conditions elicited greater activation in the right superior prefrontal cortex, left middle, superior frontal cortex, and also the right middle cingulum and caudate.

Liao & Chan (2016) ERP experiment in

processing the unexpected switch of language at the end of the sentence

Twenty-one native Mandarin-Taiwanese bilinguals with more frequent use in Mandarin

An unexpected language switch generated a widespread N400; shorter time will be required by participants in response to non-mixed sentences as compared to mixed-sentences. The language switch condition recruited higher cognitive control and longer processing cost while comprehending unexpected switch of language.

In sum, through the investigation of pathological patients, electrophysiological and neuroimaging studies, most reviews have suggested that the underlying mechanisms of language switching and mixing varied (Herschmann & Pötzl, 1920; Pötzl, 1925, 1930; A Leischner, 1948; Green, 1986; Lebrun, 1991; Aglioti & Fabbro, 1993; Martin et al., 1994;

Fabbro & Paradis, 1995b; Aglioti et al., 1996; Fabbro et al., 1997; Fabbro, 2001a; Abutalebi &

Green, 2008; Ansaldo et al., 2008), while some reviews are unable to distinguish between these two phenomenon due to similar brain activations (Mariën et al., 2005; Abutalebi & Green, 2007;

Adrover-Roig et al., 2011). Therefore, this brought us back to our first research question as to whether we can differentiate language switching and mixing at the biological level.

Furthermore, many studies on healthy individuals did not examine language switching and mixing with a complete sentence or meaningful utterances, but solely with a series of unrelated words, digits or pictures (Price et al., 1999; Hernandez et al., 2000; Hernandez et al., 2001;

Jackson et al., 2001; Wang et al., 2007). Our study added to the literature and used switching and mixing sentences as materials.