Learning a new language makes you forget other languages

Learning words in a new foreign language makes it more difficult to remember those same words in another foreign language. That is the conclusion of a research study by Kristin Lemhöfer, Psycholinguist at Radboud University and The Donders Institute, and her colleagues. For the first time, a situation for which there was only anecdotal evidence was replicated under controlled conditions.

’You sometimes hear people say that they used to be good at French until they started learning Spanish,’ says Kristin Lemhöfer. ’We wanted to find out what actually happens at such moments and whether we could mimic this process in the lab.’ Participants were first tested on their word knowledge: they were shown pictures, asked for the English word for what they saw, and then asked to learn half of the English words they already knew in Spanish as well. ’We checked immediately afterwards to see whether those English words had become less accessible. In particular, we saw that the speed with which test subjects came up with the words had decreased.’


This process of forgetting got worse after two nights of sleep. ’Sleep does a lot to our memory. At night, you reinforce what you have learnt during the day, and you also start throwing things out of your memory that you don’t think are important,’ says Lemhöfer. In this study, after two nights of sleep, subjects were not only slower but also less accurate in their English words than immediately after learning the Spanish words. ’You could say that Spanish got in the way, so they could no longer access their English memory.’


Previous research has shown that people forget things when they do not use certain knowledge, or because of competition from other memories. ’In this research study, we see that it is mainly this competition with other memories that is the problem. The Spanish words crowd out the English ones and you have a harder time getting to the English ones.’ This means that if you take a Spanish course, chances are your English will deteriorate. But this is something you can prevent. ’It’s mostly a matter of continuing to practise your English; if you do so, you will be able to speak several languages without any problems.’

Literature reference

Mickan, Anne, et al. EXPRESS: New In, Old Out: Does Learning a New Language Make You Forget Previously Learned Foreign Languages? 29 May 2023, p. 174702182311813-174702182311813, https://doi.org/10.1177/1747021­8231181380