In a global world, knowing multiple languages can afford a variety of economic and social advantages. Currently more than 50% of the world population fluently speak more than a single language. In the United States, there has been a steady increase in bilingualism since the 1980s. Does knowing multiple languages also afford cognitive advantages? There has been a great deal of interest surrounding the “bilingual cognitive advantage” hypothesis - a hypothesis that states that speaking multiple languages strengthens executive functioning.

Early research on this subject demonstrated that bilinguals, people who regularly and fluently speak more than 2 languages, outperform monolinguals in a wide range of executive function tasks such as conflict monitoring [1-4], working memory [5, 6], task switching [7] and attentional control [8]. The well-known Stroop paradigm has been widely used to study inhibitory control and interference effects across a wide range of populations. In the classic Stroop task [9], participants are presented with colour words (GREEN) printed in different colour ink (red ink) and the task requires participants to name the colour of the ink (say “red’), ignoring the word (GREEN). Slower reaction time to incongruent stimuli (red ink of word GREEN) compared to congruent stimuli (red ink on word RED) demonstrates an interference effect due to the presen tation of conflicting information. Studies have found that bilinguals are faster than monolinguals in their ability to inhibit inappropriate stimuli [10-12]. Studies using other types of tasks such as word-learning and problem-solving have also demonstrated bilingual cognitive advantages compared to monolinguals [13-16].

The bilingual cognitive advantage presumably derives from bilinguals’ extensive experience in managing two or more languages from an early age. When multiple, competing words are activated, bilinguals must select words from the appropriate language and inhibit words from the other language. Bilinguals become practiced at switching, inhibiting, and shifting between languages, and this has lead researchers to claim that bilinguals enjoy an enhancement of domain general executive functioning.

Recent scientific reviews on this issue, however, indicate that the “bilingual cognitive advantage” may be overstated. There is a heated debate on the benefits of bilingualism and whether or not the ability to speak multiple languages enhances domain general executive functioning. One camp argues that bilingual advantages exist across domains and tasks, and that there is general enhancement of cognitive functioning. The other camp argues that the benefits of bilingualisms are more complex - that advantages, if they exist, are small and task specific. A growing number of studies support the latter view and have reported no cognitive benefits of bilingualism or have reported only small effects [4, 17-21]. A review by Paap, Johnson [21] found that the bilingual advantage was reported mostly in studies using small sample sizes but not when larger samples were used. Furthermore, analyses conducted by de Bruin, Treccani [22] reveals that a publication bias exists in the field. Studies reporting a bilingual advantage are more likely to get published than studies challenging the benefits.

The present experiment re-examine the “bilingual advantage” hypothesis using linguistic material in a taboo Stroop task. We explore whether bilinguals exert better inhibitory control over emotional linguistic stimuli compared to monolingual participants. In this task, like the colour Stroop task, participants are asked to name the colour of the ink/font that the word is presented in, and not name the word itself. However, unlike the colour Stroop task that uses colour words, the words in the taboo Stroop task are taboo words (words that elicit a strong emotional reaction). The response time to name the colour of taboo words is compared to response time to name the colour of neutral words. Studies using the emotional Stroop task demonstrate that colour naming times to emotional words are slower than colour naming times to neutral words, and therefore, taboo words are responded to more slowly than neutral words [23]. The literature suggests that in a Stroop task, emotional words produce a greater interference effect compared to neutral and positive words [24, 25]. The current study examines whether monolinguals and bilinguals differ in their ability to inhibit emotionally charging words. If bilinguals are faster or more accurate to name the colour of taboo words compared to monolinguals, this would be consistent with the bilingual advantage.

Contrary to earlier studies demonstrating a bilingual advantage, we found that bilinguals were significantly slower compared to monolinguals on the taboo Stroop task which is a task designed to test executive function and interference control. That is, we did not find a “bilingual cognitive advantage” in our young adult college population. A similar study using a Stroop task to test bilingual Spanish-speaking children also failed to demonstrate faster inhibition times in bilingual elementary school children compared to monolingual children [28]. Studies of bilingual benefits suggest that developmental differences may underlie differences in executive functioning, with older adults being more likely to demonstrate cognitive advantages [4, 29]. For example Bialystok [29] found that bilingual adults over the age of 60 showed an increase in performance on tasks of inhibitory control, however, young adults did not consistently show the advantage except in the most difficult task conditions. We recognize that performance differences may become more pronounced with aging and that subtle bilingual benefits may emerge later in life. Our limited sample cannot address this possibility, and future work should examine the longitudinal cognitive changes observed in bilingual populations.

Fig. (1). Main effect of Word Type. Mean reaction times of participants to neutral and taboo words.

Fig. (2). Mean reaction time on the Stroop task.

Fig. (3). Effect of language. Difference in mean reaction times of monolinguals and bilinguals in the Stroop task.

Our results are consistent with research suggesting that in some circumstances, bilinguals experience disadvantages, particularly in tasks that involve verbal information [30, 31]. Activating multiple words/languages comes with a cost depending on the task demands [29, 32]. This disadvantage is often documented in bilingual children and the literature suggests that some bilingual children experience reduced verbal fluency [10, 33, 34]. Our work contributes to the body of work suggesting that bilingual benefits are more complex than previously believed. The bilingual cognitive advantage may be present in some cognitive domains (e.g., set shifting, non-linguistic tasks) but it is not present across all executive function tasks.

In our study we also found that taboo words were better recalled compared to neutral words, and taboo words were responded to more slowly than to neutral words [24, 26, 35]. This pattern of results held for both monolingual and bilingual participants. Our results are consistent with the priority-binding theory that states that emotionally-salient stimuli (i.e., taboo words) are given priority in encoding and binding compared to emotionally neutral stimuli [24, 36]. Emotional memories trigger binding mechanisms that allow subjects to have an increased accuracy for contextual information. This contextual information results in enhanced memory for taboo words. Previous studies with taboo words have also shown that taboo words evoke greater physiological response compared to neutral words consistent with the claim that taboo words elicit an emotional reaction in participants [37]. For example, a study examining the effects of taboo words on skin conductance levels demonstrated that conductance levels were higher on average when taboo and negative words were presented than when positive and neutral words were presented [37]. Our results lend additional support to the findings that taboo words are better recalled than neutral words, and that taboo words create greater interference in the Stroop task compared to neutral words.

Importantly, our work supports the recent critical claims that bilingualism does not enhance general executive functioning [19, 21]. This is not to suggest that the bilingual advantage does not exist. We suggest that bilingual cognitive advantages manifest in a domain specific and task specific manner, rather than as a broad, domain free enhancement of executive functioning.