Switching/Mixing Direction

After examining the switching and mixing effects, we turned to the language factor and explored how switching and mixing were modulated by this factor. Figure 7 and Table 8 show the activation regions in the Mandarin and English conditions, respectively.

Figure 7: The language effect of Mandarin and English conditions. These brain maps were produced at p < .001, uncorrected, cluster size = 10, z = 0 to 44. The precise co-ordinates are shown in Table 8.

As can be seen in Figure 7, both languages seemed to exhibit similar activations, but a more detailed inspection of Figure 7 and Table 8 suggested that English condition has a wider spread of activation regions compared to Mandarin. This indicates that it was harder for participants to process English sentences than Mandarin ones. In other words, the non-dominant language (English) activated more brain regions than the non-dominant language (Mandarin). Therefore, we can infer that our participants’ proficiency level in Mandarin and

English are not the same, with the processing of English sentences harder than the

comprehension of Mandarin sentences.

Table 8: Language effect

Anatomical location x y z Z-value

Mandarin

L precentral gyrus (BA4) -54 -12 44 6.28 R middle occipital gyrus 42 -70 0 5.38

L sub-gyral (BA37) -44 -46 -14 5.26

L inferior frontal gyrus (BA47) -48 28 0 4.29 English

L precentral gyrus (BA6) -50 -6 46 7.39 R superior temporal gyrus (BA22) 64 -10 0 6.79 R medial frontal gyrus (BA6) 6 -22 62 4.99 R middle occipital gyrus (BA37) 52 -72 2 4.7

L superior frontal gyrus -8 50 38 4.5

After analyzing the language effect, we then tested how switching and mixing were modulated by language. Figure 8 shows the participants’ brain maps in performing various tasks in Mandarin and/or English, including MM, EE, Switching EM, Switching ME, Mixing EM and Mixing ME. Visual inspection revealed that both the EM and ME conditions seemed to trigger more activity than the non-switched/mixed conditions. To examine the language direction effect of switching/mixing, the comparisons of EM vs. EE and ME vs. MM were

conducted for both mixing and switching conditions as shown in Figures 10 and Tables

9-10 .In this part of analysis, we used a lower threshold (p < .001, uncorrected, cluster size = 10) to explain our data.

Figure 8: The activated regions in the non-switched/mixed MM, non-switched/mixed EE, Switching EM, Switching ME, Mixing EM and Mixing ME conditions. These figures were produced at p < .001, uncorrected, cluster size = 10, z = 0 to 44.

In language switching, different activation patterns were found in different directions. In the contrast between EM and EE, the activated areas were the left middle frontal gyrus, left inferior parietal lobule (BA40) and right precuneus, while in the contrast of ME and MM, left precentral gyrus, left superior frontal gyrus and left inferior frontal gyrus (IFG) were

activated (see Figure 9). Directly comparing these two contrasts, we found that EM vs. EE activated mostly the parietal regions (expect the left middle frontal gyrus), but ME vs. MM activated mainly the frontal lobe, suggesting that the latter was associated with more cognitive control and task demands (see Figure 9). To verify our finding in direction, we

considered the total volume of the activated cluster-size (KE). Indeed, we found that the KE in the EM vs. EE comparison activated a smaller total volume (KE = 93), while the ME vs. MM comparison induced larger activation (KE = 306), revealing that the switch from Mandarin to English required extra cognitive effort (See Table 9).

Figure 9: The first contrast (colored in red), Switching EM vs EE, overlay with the second contrast (colored in yellow), Switching ME vs MM, to investigate the differences between these two. Regions of activations were found in the left middle frontal gyrus, left inferior parietal lobule (BA40) and right precuneus for the EM vs EE contrast. Whereas, the

activations were found in the left precentral gyrus, left STG and left IFG for the ME vs. MM comparison. These brain maps were produced at p < .001, uncorrected, cluster size = 10, x-axis = 0 to 44. The precise co-ordinates are shown in Table 9.

Table 9: The activation regions comparing the language switching in both directions with non-switching conditions. The volume of the cluster-size (KE) was listed.

Anatomical location x y z Z-value KE

Switching EM vs. EE

L middle frontal gyrus (BA9) -44 36 30 4.25 61 L inferior parietal lobule (BA40) -44 -48 60 3.52 10

R precuneus 2 -76 46 3.45 22

Total: 93 Switching ME vs. MM

L precentral gyrus (BA6) -52 -2 46 4.42 89

L superior frontal gyrus (BA6) -4 6 58 3.89 59 L inferior frontal gyrus (BA45) -50 30 8 3.72 158

Total: 306

As for mixing, there was no activated region found in the EM vs. EE comparison.

However, ME vs. MM activated the left inferior frontal gyrus (IFG, BA46 and BA47), showing that extra cognitive effort was required when perceiving Mandarin to English mixing sentences (see Figure 10). Table 10 summarizes the activated regions and the contrasts in various directions between language mixing conditions and non-mixing

conditions. Note that we did not report the cluster size in Table 10 because the corresponding comparison (EM vs. EE) showed no significant activation.

Figure 10: Mixing direction: a figure portrayed the activation pattern in the comparison between ME vs. MM sentences. Activation was found to be located in the left inferior frontal gyrus (BA47). This figure was produced at p < .001, uncorrected, cluster size = 10. The anatomical position for this figure are x=-44, y=24, z=-8. The precise co-ordinates are shown in Table 10.

Table 10: Directionality effect in mixing vs. non-mixing comparisons.

Anatomical location x y z Z-value

Mixing EM vs. EE - - -

Mixing ME vs. MM

L DLPFC (BA46) -46 24 16 3.99

L VLPFC (BA47) -44 28 -10 3.64

In sum, although the activation patterns in language switching and mixing looked similar (see Table 7), the results of comparisons in terms of switching/mixing direction revealed that switching and mixing from dominant (Mandarin) to a less dominant (English) language induced higher processing cost than the other way round.

Chapter Five

Discussion and Conclusion

There are two main research questions to address in this experiment. First, we would

like to investigate if language switching and mixing can be distinguished at the biological level. Specifically, we would like to find out if we can observe linguistically induced involvement in both language mixing and switching conditions while a more pragmatically induced activations in language switching. Secondly, to explore if the direction of language

switching or mixing (Mandarin to English or English to Mandarin) would pose any

differences in terms of processing cost. The questions were investigated through an auditory fMRI experiment conducted in the current study.