In certain areas of the world, monolinguals are in the minority. Canada and Europe have reported rates of 55% and 67% bilingual populations, respectively, whereas India and the United States report 25% and 20%, respectively, thereby showing regional differences in bilingualism [2]. Recently, there has been an increase in the number of people who want to learn a second language, which may be due to increasing globalization or the desire to learn languages passed down by parents. However, in addition to the drive to teach children multiple languages at a young age, there has been concern regarding developmental consequences on bilingual children.

There is a lot of discourse surrounding the advantages and disadvantages of learning two languages at a young age, especially since children are known to “code-mix,” which involves using both known languages in the same sentence. Code-mixing may result in further concerns regarding whether a child is “confused” on the differences between both languages and the grammatical rules that make each unique. However, code-mixing is usually not a negative sign as children are known to mimic their surroundings in which parents may alternate between multiple languages in conversation with each other. Additionally, children may not yet know certain words in one language and therefore use both to complete a full sentence [1]. In this manner, children are using all the information they have readily available to communicate. Some studies have even shown that they can adjust their choice of language with a stranger based on their first meeting, despite no prior knowledge of their skills. Additionally, they are sensitive to the stranger’s proficiency in both of the toddler’s languages and can adjust their speech accordingly, but some code-mixing may still occur [4].

Infants, similar to adults, can differentiate between two languages based on their sounds. However, studies show that past the age of 8 months, only bilingual infants focus on facial movements when determining which language is being spoken [1]. Furthermore, a study by Kuipers & Thierry (2012) showed that infants aged 2-3 years experience different neural responses to their two languages. Using event-related potentials in the brain, which are voltages measured in response to a stimulus, bilingual children were observed noticing a switch in language faster than monolinguals ‒ a pattern also seen with adult bilinguals and monolinguals [6].

The Morini Newman study was done on English and Spanish speaking toddlers (18-24 months) in which they were split into three conditions regarding word recognition: a stimulus consisting of one target word (“ball”), a same language sentence consisting of the target word at the end (“where’s the ball?”), or a mixed language sentence with the majority of the sentence in one language and the target word in the other (“dónde está la ball?”). The results are presented below in Figure 2. It can be seen that children were more likely to accurately recognize the target when prompted by a sentence rather than a single word. Additionally, there was greater accuracy observed when using the same language in a sentence over mixed languages. However, there was no statistical significance (p = 0.70) between the mixed language and single word conditions. Researchers believe that there may be “processing costs” when trying to comprehend both languages, which supports the idea that children are aware of the fact that two languages were used and must make the switch accordingly [7]. An older study also found that bilingual children realize early in their development that they are being exposed to two distinct languages rather than one language with diverse grammatical rules and sounds [5].

Similar to the Morini & Newman (2019) experiment, the study by Byers-Heinlein et al. (2017) also found that bilingual infants suffer a language processing cost during mixed language stimuli, which results in lower target word recognition compared to same sentence stimuli. However, this study found that this processing cost may be beneficial as using continuous same-language words helps bilinguals recognize, process, and switch to the language being spoken faster [3].

Furthermore, the researchers looked at pupil dilation as an indicator of “cognitive load,” which may increase during processing difficulties [3]. The experimental setup is shown in Figure 3. It was found that bilingual infants and adults showed greater dilation in the switched language block than the same language block, confirming the extra processing cost seen in bilinguals, which can be seen in Figure 4 [3]. Additionally, despite the awareness of two languages and the ability to efficiently switch between both, studies have shown that bilingual toddlers display varying vocabulary sizes depending on exposure [8]. In turn, the amount of exposure dictates each participant’s dominant and non-dominant languages. There was also greater dilation seen when switching from an infant’s dominant language to its non-dominant one, thereby demonstrating increased cognitive load. Similarly, the cognitive load was decreased when an infant switched from its non-dominant to dominant language [3].

These results show that, although toddlers can competently switch between both of their languages, they may have an affinity for one in the early stages of development. Using a similar methodology as the Morini & Newman (2019) study, Potter et al. (2019) found that toddlers had greater target word recognition with target words in their dominant language in both the single language and mixed language trials. However, they were only able to recognize the non-dominant language target words when used in a single-language trial. The results are shown in Figure 5 and suggest that the processing of a language depends on the amount of exposure a child receives to the language [8].

Taking all of the previous findings into consideration, we can see that language acquisition is a complex process. However, studies have repeatedly shown that bilingual toddlers are able to comprehend and process different languages from a young age. Code-mixing may occur, and persist into adulthood, but infants are able to recognize their two distinct languages based on auditory and facial cues as well as moderate which to use depending on their conversational partner. Bilingual children may have better processing in their dominant language, but exposure and culture will dictate how one identifies with their languages over time. Nonetheless, bilingual children complete language milestones around the same age as monolingual children [3].

Regardless of the effects of bilingualism on toddlers and infants, there is an inclination for teaching children more than one language in today’s society. This may be due to the global advantages that come with speaking multiple languages or the gradual de-stigmatization of speaking a non-national language. However, it is safe to say that there is no “one size fits all” model for language acquisition, nor have studies shown that learning two languages causes significant cognitive impairment. Bilingual children may be young but they are not confused; rather they are taking in the complex nature of their surroundings and learning valuable skills that will connect them to their culture and the world they grow up in.

References

1. Byers-Heinlein, K., & Lew-Williams, C. (2013). Bilingualism in the Early Years: What the Science Says. LEARNing Landscapes, 7(1), 95–112. https://doi.org/10.36510/learnland.v7i1.632
2. Byers-Heinlein, K., Esposito, A. G., Winsler, A., Marian, V., Castro, D. C., & Luk, G. (2019). The Case for Measuring and Reporting Bilingualism in Developmental Research. Collabra: Psychology, 5(1). https://doi.org/10.1525/collabra.233
3. Byers-Heinlein, K., Morin-Lessard, E., & Lew-Williams, C. (2017). Bilingual infants control their languages as they listen. Proceedings of the National Academy of Sciences, 114(34), 9032–9037. https://doi.org/10.1073/pnas.1703220114
4. Genesee, F., Boivin, I., & Nicoladis, E. (1996). Talking with strangers: A study of bilingual children’s communicative competence. Applied Psycholinguistics, 17(4), 427–442. https://doi.org/10.1017/s0142716400008183
5. Genesee, F., Nicoladis, E., & Paradis, J. (1995). Language differentiation in early bilingual development. Journal of Child Language, 22(3), 611–631. https://doi.org/10.1017/s0305000900009971
6. Kuipers, J. R., & Thierry, G. (2012). Event-related potential correlates of language change detection in bilingual toddlers. Developmental Cognitive Neuroscience, 2(1), 97–102. https://doi.org/10.1016/j.dcn.2011.08.002
7. Morini, G., & Newman, R. S. (2019). Dónde está la ball? Examining the effect of code switching on bilingual children’s word recognition. Journal of Child Language, 46(6), 1238–1248. https://doi.org/10.1017/s0305000919000400
8. Potter, C. E., Fourakis, E., Morin-Lessard, E., Byers-Heinlein, K., & Lew-Williams, C. (2019). Bilingual toddlers’ comprehension of mixed sentences is asymmetrical across their two languages. Developmental Science, 22(4). https://doi.org/10.1111/desc.1279