Imagine you are sitting at a table covered with objects: a cabbage, a pen, a cup, a child’s shoe. A researcher asks you, in English, to “pick up the shoe”. You do it in less than a second. But a tiny camera that follows your eyes has noticed something you were not even aware of: just before you reached for the shoe, your eyes jumped to the cabbage. Why? Because you also speak French, and in French a cabbage is called chou — a word that sounds almost exactly like “shoe”.
Experiments like this one, first carried out by the psychologists Viorica Marian and Michael Spivey in the early 2000s, revealed something surprising about people who speak two languages. Even when they are using only one of them, the other one is quietly working in the background. Researchers often estimate that more than half of the world’s population uses two or more languages in everyday life, so this is not a strange exception — it is how a huge number of human brains work. The real question is what living with two languages at the same time does to the mind. The answer, as you will see, is far more interesting — and far more controversial — than the popular headlines suggest.
Two languages that never switch off
For a long time, people imagined that a bilingual brain worked like a radio with two stations: you choose one, and the other one goes silent. The “marker and stamp” experiment, and many others like it, showed that this picture is wrong. When a bilingual person hears a word, the brain activates possible matches in both languages, especially when the words sound similar. Then, in a fraction of a second, it has to decide which language is relevant and push the other one aside.
This constant competition is the key idea behind most research on bilingualism. To speak one language without accidentally slipping into the other, the brain needs a kind of internal traffic controller. Psychologists call this ability inhibitory control — the skill of ignoring information that is not useful right now. It belongs to a wider group of mental abilities known as executive functions, which also include switching between tasks and keeping information in mind while you work with it.
The logic seemed simple. If bilinguals use their mental traffic controller hundreds of times a day, just to stay in the right language, perhaps that controller gets stronger, the way a muscle grows with exercise. And if it gets stronger, perhaps it helps with other things too: concentrating in a noisy office, ignoring distractions, or switching quickly from one job to another. This idea became known as the bilingual advantage, and for about twenty years it was one of the most exciting stories in psychology.
From “confused children” to “super-brains”
It is worth remembering how recently the story was the exact opposite. In the first half of the twentieth century, many teachers, doctors and researchers in Britain and the United States believed that bringing up a child with two languages was harmful. Several studies from that period reported that bilingual children scored lower on intelligence tests, and parents were sometimes advised to speak only the majority language at home.
The problem was that those early studies were badly designed. They often compared poor immigrant children, tested in a language they barely knew, with richer children tested in their native language. Not surprisingly, the immigrant children did worse — but it had nothing to do with bilingualism itself.
The turning point came in 1962, when two researchers at McGill University in Montreal, Elizabeth Peal and Wallace Lambert, carefully compared ten-year-old children who spoke French and English with children who spoke only French. This time the groups were matched for social background. The result shocked many people: the bilingual children performed better on a range of tests, especially those that required flexible thinking.
From the 1990s onwards, the Canadian psychologist Ellen Bialystok and her colleagues published a long series of studies suggesting that bilingual children and adults were faster and more accurate on tasks that required ignoring misleading information. A typical example is a test where you must press a button according to the direction of an arrow while ignoring which side of the screen it appears on. Bilinguals often seemed to handle the conflict more efficiently. By the 2010s, newspapers were confidently telling readers that learning a second language makes you smarter, better at multitasking and more creative.
The problem with good news
Science, however, has a habit of checking its own results — and when other teams tried to repeat the bilingual advantage studies, many of them found nothing. A particularly important challenge came from Angela de Bruin and her colleagues at the University of Edinburgh. Instead of running another experiment, they looked at the research system itself.
They collected 104 abstracts about bilingualism and executive control that had been presented at scientific conferences between 1999 and 2012. Conference talks are a useful sample because researchers present their results there before anyone decides whether they are worth publishing. Then the team checked which of these studies later appeared in scientific journals.
About 63% of the studies that supported a bilingual advantage were eventually published. Of the studies that mostly or completely failed to find one, only 36% made it into a journal.
This is a classic example of publication bias: positive, exciting results are more likely to be published than boring or negative ones. As a result, someone reading only the published literature would get a much more optimistic picture than the full set of evidence actually supports. The reason is not necessarily dishonesty — editors and authors simply find “we discovered an effect” more interesting than “we found no difference”.
Later, larger analyses made the picture even less clear. A major review published in 2018 by Minna Lehtonen and her colleagues combined the results of 152 studies on adults and concluded that, once publication bias was taken into account, there was no convincing evidence that bilingualism improves executive functions in general. Other researchers, including the psychologist Kenneth Paap, have argued that the small differences found in some studies are better explained by other factors, such as education, income or cultural background.
Does this mean the whole idea was a myth? Not quite. Some scientists still believe that real but small effects exist in particular groups — for example, in people who switch between languages very often, or in older adults. What has clearly changed is the confidence. The honest summary today is that bilingualism does not turn ordinary people into mental superheroes, and if it gives an everyday cognitive boost at all, the boost is modest and difficult to measure.
A shield against dementia?
The most hopeful claim of all concerns the ageing brain. In 2007, Ellen Bialystok and her colleagues looked at the records of 184 patients at a memory clinic in Toronto. Those who had spoken two languages throughout their lives had developed the first symptoms of dementia, on average, about four years later than those who spoke only one.
Many people suspected that this result could be explained by immigration. Many of the bilinguals in Toronto were immigrants, and people who move to another country may differ in health, education or lifestyle. So a study from India attracted a lot of attention. In 2013, a team led by Suvarna Alladi examined 648 patients at a memory clinic in Hyderabad, a city where using several languages is completely normal and is not linked to immigration. Of these patients, 391 were bilingual. On average, their dementia symptoms appeared about four and a half years later — at around 65 and a half rather than 61. Remarkably, the effect was also found among patients who could not read or write, which suggests that formal education was not the hidden explanation.
How could a second language possibly delay dementia? The leading explanation is the idea of cognitive reserve. Bilingualism does not seem to stop the disease from damaging the brain. Instead, a brain that has spent decades managing two languages may build extra networks and learn to compensate, so that it can keep working normally for longer despite the damage. Brain scans support this to some extent: a 2011 study from Toronto found that bilingual patients with Alzheimer’s had considerably more physical damage in their brains than monolingual patients at the same level of symptoms.
Here too, however, the evidence is mixed. Some later studies, especially those that followed healthy people over many years rather than looking back at clinic records, found little or no protective effect. So the safest conclusion is cautious: lifelong bilingualism may help the brain cope with damage, but it is not a guaranteed shield, and scientists are still arguing about how strong the effect really is.
Does each language come with its own view of the world?
So far, we have talked about how efficiently the brain works. But there is another, perhaps even more fascinating question: does the language you are using change what you notice and how you understand events? This is an old idea, often connected with the American linguist Benjamin Lee Whorf. Its strongest version — that language completely controls thought — has been rejected. A weaker version, however, has found real support in experiments.
Consider colour. English has one basic word, blue, while Russian has two: goluboy for light blue and siniy for dark blue. In a 2007 study, Jonathan Winawer and his colleagues showed Russian and English speakers pairs of blue squares. Russian speakers were faster at telling two shades apart when the shades fell into different Russian categories. Interestingly, this advantage disappeared when they had to remember a series of words at the same time, which suggests that language was actively involved in the task.
Bilinguals add an extra twist to this story, because they carry two languages and can switch between them. A study published in 2015 by Panos Athanasopoulos and his colleagues looked at how people describe motion. German speakers tend to mention the goal of an action (“a woman is walking towards her car”), while English speakers more often describe just the action itself (“a woman is walking”), partly because the English “-ing” form focuses attention on what is happening right now.
The researchers showed people short videos of ambiguous scenes, such as a woman walking along a road with a car parked in the distance, and asked them to judge which other scene it resembled more. German speakers were more likely to see the action as goal-directed. Then came the clever part. German-English bilinguals were asked to repeat strings of numbers aloud while watching the videos — sometimes in German, sometimes in English. Keeping one language busy in this way blocked it. When English was blocked, the bilinguals behaved like German speakers; when German was blocked, they behaved like English speakers. And when the language of the numbers was changed halfway through the experiment, their way of seeing the scenes changed with it.
In other words, the bilinguals were not stuck with one fixed perspective. Their perception seemed to follow whichever language was active at that moment.
A different person in each language?
Many bilinguals say they feel slightly different depending on the language they are speaking — more polite in one, more direct or funny in another. Scientists have tried to test this feeling. In a classic study from the 1960s, the linguist Susan Ervin-Tripp asked Japanese-English bilingual women in the United States to finish incomplete sentences. When a sentence about a conflict between personal wishes and family expectations was completed in Japanese, the answers tended to express sadness or duty; in English, the same women were more likely to say they would simply follow their own wishes.
Part of the explanation is that each language is connected to different memories, cultural norms and social situations. Another part has to do with emotion. For most people, the first language feels emotionally “hotter” than a language learned later, perhaps because it was learned in childhood, surrounded by family, feelings and strong experiences. Many bilinguals say that swearing, praying or saying “I love you” feels much stronger in their native language.
This emotional distance can even change moral decisions. In 2014, a team led by Albert Costa, working with Boaz Keysar and Sayuri Hayakawa, gave 725 people a famous moral puzzle. A train is about to kill five people, and the only way to save them is to push a large stranger off a bridge onto the track, killing him. Most people refuse to push. However, when the dilemma was presented in a foreign language rather than in the participants’ native language, people were roughly twice as likely to choose to sacrifice one person to save five. The researchers called this the foreign language effect: thinking in a second language seems to reduce the emotional reaction and lets cooler, more calculating reasoning win.
Later work has shown that the effect is not simple. It is weaker in people who learned the second language very well or used it in emotional situations, such as living abroad. Still, the main lesson is striking: the same person, facing the same problem, may make a different decision depending on the language in which the problem is presented.
So, does it change how you think?
Put together, the research tells a more subtle story than the old headlines. Speaking two languages probably does not make you generally smarter, and the evidence for a big, everyday boost in concentration has become much weaker under careful examination. The possible protection against dementia is real enough to keep scientists interested, but not strong enough to be called a cure.
Yet bilingualism clearly does change something. Both languages remain active at the same time, constantly competing. The language you are using can influence what you notice in a scene, how you remember a conflict, and even how coldly you judge a moral choice. Perhaps the most accurate way to describe a bilingual mind is not as a better brain, but as a more flexible one — a mind that has learned, at least sometimes, to look at the same world through two different windows.
This raises a question worth thinking about if you are learning a language right now: as your new language becomes stronger and gathers its own memories and emotions, at what point does it stop being a tool you use and start becoming a second way of seeing things?
Sources
- Peal, E. & Lambert, W. E. (1962). The relation of bilingualism to intelligence. Psychological Monographs.
- de Bruin, A., Treccani, B. & Della Sala, S. (2015). Cognitive advantage in bilingualism: An example of publication bias? Psychological Science.
- Lehtonen, M. et al. (2018). Is bilingualism associated with enhanced executive functioning in adults? A meta-analytic review. Psychological Bulletin.
- Bialystok, E., Craik, F. I. M. & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia.
- Alladi, S. et al. (2013). Bilingualism delays age at onset of dementia, independent of education and immigration status. Neurology.
- Athanasopoulos, P. et al. (2015). Two languages, two minds: Flexible cognitive processing driven by language of operation. Psychological Science.
- Costa, A. et al. (2014). Using a foreign language changes moral decisions. University of Chicago News.
