Excerpt of a study report:
“The previous study used ultrasound to see whether fetuses recognized changes in language by measuring changes in fetal heart rate,” Minai says. “The speech sounds that were presented to the fetus in the two different languages were spoken by two different people in that study.
Speech is “muffled, like the adults talking in a Peanuts cartoon, but the rhythm of the language should be preserved and available for the fetus to hear.”
“They found that the fetuses were sensitive to the change in speech sounds, but it was not clear if the fetuses were sensitive to the differences in language or the differences in speaker, so we wanted to control for that factor by having the speech sounds in the two languages spoken by the same person.”