Multilinguals say it feels as though learning another language interferes with old ones. New research put this to the test
When Julie Sedivy’s father died, she returned home to the Czech Republic and discovered another loss: Czech, her native tongue. In her book Memory Speaks: On Losing and Reclaiming Language and Self (2021), Sedivy, a language scientist in Canada, describes her experience with language attrition – the forgetting of a language once known, even one learned long ago. For her, language attrition felt connected to her learning English, which crowded out the Czech.
‘Like a household that welcomes a new child, a single mind can’t admit a new language without some impact on other languages already residing there,’ Sedivy wrote. This is a frequent observation among multilinguals, that ‘Languages can co-exist, but they tussle, as do siblings, over mental resources and attention,’ as she put it.
A recent study in the Quarterly Journal of Experimental Psychology provides some of the first experimental evidence of this process. The study included Dutch native speakers who also knew English, but not Spanish. The participants took an English vocabulary test, and each person was assigned 46 words that they already knew. Then, they learned half of those words in Spanish.
After learning these 23 Spanish versions, the participants were again tested on all of the 46 words in English. Since they had already been quizzed on the English words once, participants were generally quicker to respond on this re-test. But, overall, they showed less of an increase in speed when recalling English words that they had also just learned in Spanish. ‘Hence,’ the researchers write, ‘we can conclude that learning words from a new language does come at the cost of at least retrieval ease for words in previously learnt foreign languages.’ In one of the experiments, learning the Spanish versions of words also seemed to make participants slightly less accurate when recalling those words in English.
Words compete in our minds, and a delay in retrieval could result from a person having to pause to select the right one
The experimenters examined whether giving the Spanish words a day to sink in would lead them to interfere more with the English versions, compared with when participants were retested the same day. But the delay didn’t make much of a difference in the results.
Past studies have suggested that learning something new can drive out other information through a memory process called interference. As far back as 1900, researchers demonstrated this by asking people to learn and remember sets of words, such as ‘rose – window, horse – cloud’, and then new sets that had only the first item in each pair: eg, ‘rose – chair, horse – balloon’. People who saw the second list had more trouble remembering the first. Words compete in our minds, and a delay in retrieval could result from a person having to pause to select the right one.
When new learning interferes with older learning, it’s called ‘retroactive interference’. This is common when learning more than one language, says Kristin Lemhöfer, the senior author on the recent paper, and an associate professor in psycholinguistics at Radboud University in the Netherlands. If you first learn that ‘dog’ is chien in French, and then you learn that it’s perro in Spanish, remembering un chien could become more effortful later.
One lingering question about retroactive interference is whether new learning can interrupt much older learning that’s been consolidated into long-term memory, rather than something learned more recently. This new study showed it’s possible; Lemhöfer was surprised that learning Spanish words impacted the recall of the English that the Dutch participants had learned many years previously. And interestingly, the experiments also revealed that interference can arise from simply learning a new language, whether or not it is used.
After seeing this interference demonstrated in the lab, Lemhöfer says it’s something that language learners should be prepared for: multilingualism may simply be taxing on the brain. Multilinguals have been shown to take longer to find and produce a word in any of the languages they speak, and they can experience tip-of-the-tongue-states more often, she says.
Lemhöfer is German, spent a year in London, and then went to the Netherlands for her PhD – so she has plenty of firsthand experience with this phenomenon. ‘When I started to learn Dutch, my English was suddenly blocked,’ she says. ‘When I tried to speak it, a lot of Dutch words came out, which was embarrassing at times. It only disappeared once my Dutch became more stable, and I spoke more English again.’
It may not be completely avoidable, but Lemhöfer thinks that these effects can be alleviated by continuing to use the language that’s being forgotten or interfered with. ‘Even though we did not empirically test that in that study, we strongly believe that the forgetting effects we observed can be avoided by continuing to use the other language, too,’ Lemhöfer says.
For Sedivy, spending time in the Czech Republic and reacclimating herself with the language was awkward at first, but the words came rushing back – and parts of herself came with them. ‘English was the language in which I forged my independence, the language of my individuation,’ she wrote in an essay in 2015. ‘But it was in Czech that I was nurtured, comforted, and sung to.’