Human beings communicate in nearly 7,000 different languages. A surprisingly—and perhaps concerningly—large number of those languages is “endangered”, with nearly 500 (or 6%-7%) being listed by UNESCO. Scholars have warned that “World languages are now rapidly being lost”, and like the loss of species diversity, this language extinction has been attributed to economic development—the more successful a country was economically, the more rapidly its languages were being lost.

One way in which languages might be lost is by the assimilation of native speakers into a new culture, and their inability to pass on their linguistic heritage to their children. For example, given that there are only 8 known speakers of the Busuu language in the world, if any of them immigrated to the U.S. and failed to pass on their language to their offspring, it would not be surprising if Busuu went extinct in short order.

What are the processes by which parents pass on their “heritage language” to their children growing up in a different linguistic environment? How can heritage language skills be fostered and protected?

A recent article in the Psychonomic Bulletin & Review tackled those issues. Researchers Gollan, Starr, and Ferreira examined the factors that determine the acquisition of a heritage language spoken at home (such as Chinese, Spanish, or Hebrew) in children who grow up in America.

The researchers invited bilingual participants to complete a language history questionnaire, which was followed by a picture-naming task in their heritage language and English (either in that order or in the reverse sequence). This simple task—seeing a picture of, say, a butterfly and saying “butterfly” (or “פרפר”)—is predictive of more complex language abilities.

The results identified two factors that determined a person’s proficiency in their heritage language: The first one was rather obvious and not unexpected. The more people spoke English during their childhood, the less they mastered their heritage language (and vice versa). The second variable was less obvious and more intriguing. The more different people a bilingual person regularly spoke to in the heritage language during their childhood, the better their heritage language skills, all other variables being equal.

This is an intriguing result because it shows that it is not linguistic “quantity” per se that matters, but also the diversity of exposure. If your aunt and grandmother also contribute to your linguistic environment, you learn more than if your mother triples her output. Indeed, Gollan and colleagues suggest that the number of different speakers might be more powerful than frequency of use as a predictor of heritage language fluency.

The results were roughly the same irrespective of whether the heritage language was Spanish, Chinese, or Hebrew.

So why would diversity matter so much? What makes it easier to learn Spanish at home when there are three speakers rather than one who speaks the same amount?

There is a large literature in cognitive psychology on the important role of contextual diversity in learning generally: we learn better when episodes are spaced apart in time or when material is presented in multiple different contexts (e.g., in different learning environments, such as school vs. work). Even for over-learned stimuli, such as our knowledge of words, contextual diversity—rather than, say, word frequency—predicts how quickly we can recognize and read a word. That is, it is the number of different passages or documents in which a word occurs that supports our knowledge more than the simple number of times we have encountered a word.

The research by Gollan and colleagues thus extends a theme that has become a main plank of current cognitive knowledge: repetition alone does not build better memories. Indeed, we now know that even 1,000 (or more) exposures to a message do not guarantee its accurate uptake. What is required to build effective memories and to acquire skill is contextual diversity.

So if you are one of the last Busuu speakers, then your language might stand a better chance of survival if you emigrate together with the other 7 remaining speakers rather than on your own—no matter how much you plan to speak to your children in Busuu.