How thinking in a foreign language makes you more rational in some ways but not others

Back in 2012, US researchers showed that when people used their second, non-native language, they were less prone to a mental bias known as loss aversion. This bias means we're averse to the same outcome when it's framed in a way that highlights what's to be lost, as compared with when it's framed in a way that emphasises what's to be gained. For example, a vaccine is more appealing if it's stated that it will save 200,000 out of 600,000 people; far less appealing if it's explained the vaccine means 400,000 will die. In a sense then, the US research suggested that using a second language makes our thinking more rational.

Now Alberta Costa and his colleagues have investigated the limits of this "foreign language effect". "… [M]any people in today's world interact and make decisions in a foreign language making it crucial to understand how decisions are affected by language," they said.

In all, the researchers tested over 700 people. Most were Spanish students whose first language was Spanish, but who also spoke English learned in a classroom. Some native Arab speakers were also tested (second language Hebrew), and some native English speakers (second language Spanish).

Costa's team first tested their participants on decision-making tasks that involved loss aversion and other forms of uncertainty. For example, they used the Ellsberg Paradox in which participants were offered the chance of rewards if they picked the right coloured token (black or red) out of a jar where they knew the balance of colours (50-50), or out of a jar where they didn't know the balance. The Ellsberg Paradox describes the fact that people usually prefer to make successive gambles from the jar where they know the balance, even though this behaviour suggests they sometimes think first jar has a higher proportion of one colour than the second jar, and yet other times they think it has a higher proportion of the other colour – a logical impossibility.

The main result here was that the participants tended to show less irrationality when completing these decision-making tasks in a foreign language. A feasible explanation, the researchers said, is that the emotional element of these kinds of tasks – ones based on uncertainty and fear of loss – usually encourages more intuitive, less rational thinking. But when a second language is used, this dulls the emotional intensity of the decisions, thereby encouraging deeper, more rational thought.

If this explanation is correct, then we'd expect the foreign language effect to be absent or reduced for decision making tasks that are emotionally neutral. That's exactly what Costa and his colleagues found. For example, the participants completed several tests of cognitive reflection. These involved questions like "If it takes 5 machines 5 minutes to make 5 keyboards, how long would it take 100 machines to to make 100 keyboards?" Answering these questions correctly involves deliberate reflection, and answers based on intuition tend to be wrong. This time, there was no evidence of a foreign language effect – participants tended to answer these kinds of questions wrongly even when using their second language.

Costa and his colleagues acknowledged there's lots more research to be completed on the foreign language effect. Other possible factors at play include effects of cognitive fluency and cognitive load – the mental effort of speaking a foreign tongue. For now, however, the results are consistent with the idea that using a second language can make us more rational on decision tasks that have an emotional element. If you're bilingual and confronted with such a decision, it could be worth thinking it through in your second tongue. Bonne chance!
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Costa A, Foucart A, Arnon I, Aparici M, and Apesteguia J (2014). "Piensa" twice: on the foreign language effect in decision making. Cognition, 130 (2), 236-54 PMID: 24334107