[pmr_]

Neither of the two languages a bilingual person speaks is considered foreign. Otherwise the person would not be bilingual. What would be the result of such a study? Keep in mind that in linguistics the difference between being a native speaker and having learned a language after the critical period is considered huge.

[mercer]

The critical period is until around the age of seven, right? The reason I'm asking is that I started speaking/reading a lot of English from the age of 8 on, and as far as I can tell I'm bilingual. Could you explain why that would not be the case, or how that's possible?

[barry-cotter]

tl:dr It's fluency that impacts utilitarianism, not nativeness.

Being able to communicate in two languages is not the same as being bilingual. The study in question suggests that thinking/communicating in a language that one is less than fluent in leads to more utilitarian decisions.

The important thing here is fluency, not nativeness. I am fluent in German but I started learning it at 12. German is not a native language for me but I am fluent in it. As such the study suggests I should be equally utilitarian in it and English, my mother tongue. But my French and Mandarin are both quite bad so I should be more utilitarian in them because I must be more deliberate.

[TazeTSchnitzel]

Right. Presumably for a bilingual person (where both languages are native), both languages they speak would have equal emotional impact.