Jimena Santillán: Inhibitory Control in the Bilingual Brain: Testing the Bilingual Advantage Hypothesis

Graduate Student Research

Jimena's-PosterIt has been proposed that when bilinguals want to speak one of their two languages the representations of both languages get activated. Thus, in order to be able to speak the language they want to speak, the representation of the other language has to be inhibited. If bilinguals are constantly engaging in this process then their inhibitory control, the ability to suppress irrelevant representations to favor relevant ones, might get exercised. This proposal has led to the question of whether the practice in inhibitory control that bilinguals obtain translates into benefits that extend beyond the language domain.

Evidence from research studies showing that bilinguals outperform monolinguals in tasks requiring inhibitory control has led to the claim that a “bilingual advantage,” exists. This has received a lot of media attention. However, from a scientific standpoint the bilingual advantage hypothesis remains controversial, as the evidence for it has been inconsistent. Most studies putting this hypothesis to the test have relied on looking at differences in behavioral outcomes, such as accuracy or reaction time on tasks requiring inhibitory control. Some of these studies find that bilinguals outperform monolinguals, while others find no differences between the two groups.

Inhibitory control is a fast occurring process that occurs at the brain level, so being able to look at what is happening in the bilingual and the monolingual brain during inhibitory control processing would provide a powerful test of the bilingual advantage hypothesis. A cognitive neuroscience technique known as “event-related potentials” allows researchers to measure how brain processes unfold in real time. The technique involves using a cap embedded with electrodes that rest on the scalp to measure the electrical activity that the brain naturally produces.

The present study, supported by a summer Graduate Research Grant from the Center for Latino/a and Latin American Studies, employed the event-related potential technique to examine if there are differences between bilinguals and monolinguals at very early stages of inhibitory control processing. Participants consisted of 11 English monolinguals and 11 Spanish-English highly balanced bilinguals who acquired both languages during childhood. The two groups did not differ in terms of age, gender, English language proficiency, education level completed, or socioeconomic status. This ensured that any differences in inhibitory control observed would not be the result of differences between the groups in these variables, which has been a limitation of previous studies.

Participants listened to two different children’s stories presented simultaneously on speakers, one on their left and one on their right, and were asked to attend to one of the stories while ignoring the story coming from the other side. To help them remember which side to attend to, they watched images on a computer monitor that matched the story they were supposed to be attending. Identical sound probes were embedded in both stories, which allowed us to compare the brain response to the exact same probes when they appeared on the attended story to when they appeared on the unattended story. The prediction was that if participants were effectively enhancing the signal of the attended story and inhibiting the signal of the unattended story, their brain responses elicited by the probes embedded in the attended story would be amplified, and the ones elicited by the probes embedded in the unattended story would be suppressed. In line with the bilingual advantage, we predicted that this attention modulation would be observed earlier for bilinguals, reflecting better inhibitory control.  As early as 100 milliseconds after they heard the sound probes, bilingual participants showed the expected attention modulation, while monolingual participants did not show a difference at this very early time window. This evidence suggests that bilingual participants were exerting inhibitory control to be able to attend to the relevant story and inhibit the irrelevant story beginning at very early stages of inhibitory control processing, which occurred at three times faster the average rate at which we blink! This early difference could not have been detected without using the event-related potential technique.

My future research will continue to put the bilingual advantage hypothesis to the test, as accumulating scientifically rigorous evidence for its existence could have implications for instigating bilingual education at an early age, and would provide evidence to encourage Latino/a families to raise their children as bilingual.

—Jimena Santillan is a second year doctoral student in the Cognitive Neuroscience program at UO. As part of the Brain Development Lab, her research examines the effect of environmental factors on neuroplasticity, with the goal of identifying potential protective factors that counteract the deleterious effects on brain development caused by growing up in poverty.