Abstract:

It has been estimated that more than half of the world’s population is bilingual. In the past few decades, numerous studies have shown that bilinguals have an advantage in selecting relevant information, inhibiting competing and distracting information than monolinguals (e.g., Bialystok, Craik, Klein, & Viswanathan, 2004; Costa, Hernández, & Sebastián-Gallés., 2008, to name just a few). Recent research has instead shown a more nuanced story: bilinguals and monolinguals perform equally in either the Stroop or flanker task (Paap & Greenberg, 2013; Sawi & Paap, 2013). To date, it is still hard to confirm that bilinguals have an advantage in language inhibition. While the vast majority of bilingual research has exclusively focused on the study of spoken language users – ‘unimodal’ bilinguals, bimodal bilinguals have received scant attention. ‘Bimodal’ bilinguals, who have acquired a spoken and a signed language, can provide a unique testbed for the bilingual advantage effect. In addition, few studies have looked at whether different second language proficiencies contribute to the same language inhibitory ability in unimodal and bimodal bilinguals. Therefore, the current study examined language inhibition ability in unimodal (English-Chinese) and bimodal (English-American Sign Language) bilinguals with both low and high L2 proficiency.

In Experiment 1 and 2, a homograph interference task was used to investigate bilingual advantage in conflict resolution during sentence processing. Participants were asked to read a sentence ending with a homograph (e.g., He walked along the bank.) and then judge if a target word (e.g., RIVER or MONEY) matched the meaning of the sentence they just read. Although the target word (e.g., MONEY) is semantically related to one meaning of the homograph (bank: a financial institution), it is not the meaning supported by the sentence context (e.g., He walked along) and, consequently, this alternative meaning must be suppressed in order to correctly respond “no”. Thus, a measure of homograph interference can be computed by comparing the mean RT for the target words semantically relevant to the sentences or not.

Experiment 1 showed that the unimodal bilinguals with higher L2 (Chinese) proficiency outperformed the unimodal bilinguals with lower L2 proficiency and the monolinguals on the homograph interference task that required resolving conflict from competing alternative meanings. In addition, there was no difference between the unimodal bilinguals with lower L2 proficiency and the monolinguals. In Experiment 2, there was no performance difference in the homograph interference task between the bimodal bilinguals with higher L2 (American Sign Language) proficiency, the bimodal bilinguals with lower L2 proficiency and the monolinguals. Taken together, the results across the two experiments indicate that both L2 modality and L2 proficiency are mediating factors of bilingual advantage effect.

According to the results of the two experiments, one possible explanation for this enhancement of language inhibitory ability in unimodal bilinguals is that the regular use of two languages requires a mechanism to select the target language and inhibit the non-target language—an experience that may enhance general control mechanism. By contrast, bimodal bilinguals can always sign (gesture) and speak at the same time. The comprehension and production of their two languages involve distinct sensory-motor and perceptual systems, leading to weaker demand on language inhibition. Together, these results attribute the bilingual advantage in linguistic inhibition ability to the unimodal bilingual’s experience of controlling two languages in the same modality.

Key words: bilinguals, language inhibition, L2 proficiency, cognitive advantage effect, modal