Neural Evidence of Language Membership Control in Bilingual Word Recognition: An fMRI Study of Cognate Processing in Chinese-Japanese Bilinguals

Abstract

This study aims to examine the neural mechanisms of resolving response competition during bilingual word recognition in the context of language intermixing. During fMRI scanning, Chinese-Japanese unbalanced bilinguals were required to perform a second-language (L2) lexical decision task composed of cognates, interlingual homographs, matched control words from both Chinese (first language) and Japanese (L2), and pseudowords. Cognate word processing showed longer reaction times and greater activation in the supplementary motor area (SMA) than L2 control word processing. In light of the orthographic and semantic overlap of cognates, these results reflect the cognitive processing involved in resolving response conflicts enhanced by the language membership of non-target language during bilingual word recognition. A significant effect of L2 proficiency was also observed only in the SMA, which is associated with the task decision system. This finding supports the bottom-up process in the BIA+ model and the Multilink model. The task/decision system receives the information from the word identification system, making appropriate responses during bilingual word recognition.

Keywords: bilingualism; cognates; fMRI; interlingual homographs; stimulus list composition.

FIGURE 1

Experimental design. Event-related design for the fMRI experiment.

FIGURE 2

Relationship of proficiency level with participants’ mean RT and mean accuracy rate. In (A), the x-axis indicates the bilinguals’ proficiency level. The y-axis indicates the mean RT to each L2 word type (CO, cognate; JC, Japanese control word; IH, interlingual homograph). The proficiency level was consistently related to the response to Japanese words. Higher proficiency levels were associated with faster RTs. In (B), the y-axis indicates the bilinguals’ mean accuracy rate for each L2 word type. The RT tendency in (A) was not observed in the accuracy rate data. Higher proficiency levels were associated with a relatively low accuracy rate for IHs in comparison with COs and JCs.

FIGURE 3

Brain areas observed by comparisons between types of words. In (A), the contrast of [interlingual homograph (IH) > Japanese control word (JC)] revealed significant activation of the left orbital part of the IFG and the supplementary motor area. In (B), the contrast of [cognate (CO) > Japanese control word (JC)] revealed activation in the supplementary motor area. The threshold was set at p < 0.05 after cluster-level correction (initial voxel-level height threshold, p < 0.001).

FIGURE 4

Activation patterns associated with the response to each word type. The x-axis indicates the word types (CO, cognate; JC, Japanese control word; IH, interlingual homograph; CC, Chinese control word). The y-axis indicates the mean activation level during the response to each word type. The response to pseudowords (PWs) was treated as the baseline. (A) A significant difference was observed between the responses to IHs and JCs in the word identification system, LIFG (left inferior frontal gyrus) and left insular. (B) In the task/decision system, SMA (supplementary motor area), a significant difference was observed not only between the responses to IHs and JCs but also between those to COs and JCs (*p < 0.05, **p < 0.01, ***p < 0.001).

FIGURE 5

Relationship between participants’ proficiency level and response to types of words in the SMA. The x-axis represents the bilinguals’ L2 proficiency level. The y-axis indicates the log-transformed response data of the SMA activity level. Even though significant difference could be observed from the types of words (IH, CO, and JC), the effect of L2 proficiency is inconsistent among three types of words [F(1,44) = 0.88, p = 0.35].

FIGURE 6

Chinese–Japanese bilinguals’ L2 proficiency level. The limited number of highly proficient bilinguals may be why the L2 proficiency level did not show a consistent effect on the accuracy rate and brain activation patterns.