Fetuses might be able to differentiate between languages, a new study from the University of Kansas suggests. Researchers say the differences were clear from changes detected in the fetuses' heart rhythms.

In the study, a single bilingual speaker made two recordings — one in English and one in Japanese — that were then played to the fetuses of two dozen pregnant women. English and Japanese are thought to be rhythmically distinct, providing a helpful case study in language contrast. The fetuses were on average about one month away from full term.

Using a device called the magnetocardiogram, researchers saw that fetal heart rates changed when fetuses heard the recording of the unfamiliar language (Japanese) after hearing the recording of the familiar language (English). The heart rates did not change when the familiar English recordings were played back to back.

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"These results suggest that language development may indeed start in utero," linguistics professor and lead researcher Utako Minai said in a statement. The study was published this week in the journal NeuroReport.

According to experts at the Mayo Clinic, the sense of hearing develops in the second trimester, starting at about 18 weeks of gestation. The fetus is exposed to a multitude of sounds in the womb: the rumblings of the mother's gut, her heartbeat and voice, as well as external noises.

"It's muffled, like the adults talking in a 'Peanuts' cartoon," Minai said to describe how sounds reach the womb.

(Baby Einstein consumers take note: Contrary to popular belief, there's no meaningful evidence that listening to Mozart or other musicians in utero does anything for general intelligence or cognition down the line.)

This is not the first study to affirm that babies start absorbing language while still in the womb. In 2013, a study conducted in the U.S. and Sweden showed that newborns only 30 hours old were able to differentiate between their native language and a foreign language, leading researchers to conclude that language awareness must begin even before birth. The newborns in that study sucked longer on their pacifiers when listening to foreign languages, a behavior indicating the babies were intently focused on the unfamiliar, researchers said.

The new research is unique in that it relied on a magnetocardiogram, a device that detects tiny magnetic fields that surround electrical currents in the heart. The researchers called this technology a step forward, as it captures more sensitivity in heartbeats, breathing, and other movements than the ultrasounds used in similar studies in the past.

Christine Moon, a psychology professor at Pacific Lutheran University who was not involved with the study, described the University of Kansas researchers as "very experienced" in the challenging science of fetal measurements. Moon has authored multiple studies on how fetuses learn voices and language in the womb.

"Measurements of fetal learning and cognitive development are devilishly difficult to do well," Moon told CBS News via email, adding that the study is bolstered by the fact that it was led by a linguist.

"This sort of basic research into very early learning and cognition can help in creating therapies for atypical development during a period when the brain is unusually open to change," Moon said.

Experts believe that robust sound stimulation can make a world of difference in young lives. Over the past 25 years, encouraging parents to talk, read and sing to their babies — behaviors proven to build up babies' brains — has become a top public health priority.

Those efforts kickstarted in 1995, when another team of University of Kansas researchers reported their stunning findings on the "word gap" between babies in low-income households and babies in higher-income households. The researchers found that by age 3, a poor child would have heard 30 million fewer words spoken in his or her home environment than a child from a professional family. Those differences were tightly linked to significant differences in IQ and academic success down the road. That research spurred hundreds of follow-up studies and programs to encourage healthier child development, from the local level to the White House.

The new research sheds light on the complexity and sensitivity of fetuses' brains just before birth.

"Fetuses are tuning their ears to the language they are going to acquire even before they are born, based on the speech signals available to them in utero. Pre-natal sensitivity to the rhythmic properties of language may provide children with one of the very first building blocks in acquiring language," Minai said.