As a reader of the research paper, another limitation of the study is that the study did not appear to differentiate between people who learned a second language as an adult, versus people who grew up bilingual.
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To add context on how participants self-reported their bilingualism, the authors wrote: "To obtain information about the number of languages spoken, which languages were spoken, and demographic variables (such as age, country of origin, SES, and education), we asked participants to complete a detailed questionnaire. The questions used in the present study are available in Appendix S1 in the Supplemental Material available online."
From the downloaded supplementary material, the only questions asked related to language assessment were:
"5. What language(s) do you primarily speak at home?
"6. How many languages do you speak?
Select one: 1-20"
I could not find any other questions related to language assessment.
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From the questionnaire, it looks like the researchers did not examine whether studying a second language as an adult to a very high level could confer cognitive advantages. The study possibly treated people who grew up bilingual and didn't acquire a second language as an adult, and also people who self-reported as bilingual but did not reach a high level in the language, into the same group.
The conclusions of the study would be stronger if the researchers examined how the cognitive abilities of monolingual people who undergo training in a second language and practice it to an advanced level, could change their cognitive abilities over time.
In fact, it remains plausible that adult language acquisition could still provide cognitive benefits. Another research paper with conflicting conclusions [1] studied the effect of language acquisition on older adults aged 59–79 years old. The authors of this different study concluded that "learning a foreign-language may represent a potentially helpful cognitive intervention for promoting healthy aging."
~~
To add context on how participants self-reported their bilingualism, the authors wrote: "To obtain information about the number of languages spoken, which languages were spoken, and demographic variables (such as age, country of origin, SES, and education), we asked participants to complete a detailed questionnaire. The questions used in the present study are available in Appendix S1 in the Supplemental Material available online."
From the downloaded supplementary material, the only questions asked related to language assessment were:
"5. What language(s) do you primarily speak at home?
"6. How many languages do you speak? Select one: 1-20"
I could not find any other questions related to language assessment.
~~
From the questionnaire, it looks like the researchers did not examine whether studying a second language as an adult to a very high level could confer cognitive advantages. The study possibly treated people who grew up bilingual and didn't acquire a second language as an adult, and also people who self-reported as bilingual but did not reach a high level in the language, into the same group.
The conclusions of the study would be stronger if the researchers examined how the cognitive abilities of monolingual people who undergo training in a second language and practice it to an advanced level, could change their cognitive abilities over time.
In fact, it remains plausible that adult language acquisition could still provide cognitive benefits. Another research paper with conflicting conclusions [1] studied the effect of language acquisition on older adults aged 59–79 years old. The authors of this different study concluded that "learning a foreign-language may represent a potentially helpful cognitive intervention for promoting healthy aging."
[1] https://www.frontiersin.org/articles/10.3389/fnins.2019.0042...