Sheep study spies on what a fetus can hear.
2 February 2003

MICHAEL HOPKIN

A team of US researchers has made an inventive attempt to discover how much an unborn baby can hear in the womb — by making recordings from the inner ear of a fetal sheep.

They found that low frequencies reach the womb with ease, whereas higher-pitched sounds are more muffled. This implies that vowel sounds — the 'melody' of speech — reach the fetus's ears, says Ken Gerhardt of the University of Florida, who led the study. But consonants, which are spat out at higher frequencies, are obscured. "A fetus would hear the low notes on a piano but probably not the higher ones," Gerhardt says.

The researchers made the recordings by removing a sheep fetus from the womb and inserting tiny electrodes into its inner ear. The implants picked up the electrical signals generated in the ear in response to sound. The team then returned the fetus to the womb and played it human speech through a loudspeaker next to its mother's body.

When the researchers asked human volunteers to listen to sounds recorded in the womb, the listeners correctly identified only about 40% of the words1.

The recordings should be very similar to how an unborn baby would hear voices, including that of its mother, says developmental psychologist Anthony DeCasper of the University of North Carolina-Greensboro. So a baby in the womb would presumably hear the muffled sing-song of speech without much definition. "It would be like Lauren Bacall speaking from behind a heavy curtain," says DeCasper.

Animal of choice

Gerhardt is confident that the acoustics of human and sheep wombs are roughly the same. "It's all inferential of course," he says, "but the sheep is generally the animal of choice for pregnancy research."

The study adds to our understanding of what it's like to be an unborn baby. Revealing how sound reaches infants could help us to understand how hearing and speech develop after birth, for example.

The fact that the womb's walls soak up sound from outside will be a relief to those concerned about the effect of outside noise on unborn babies. Health experts had worried that expectant mothers who work in loud factories or attend rock concerts might be putting their children's hearing at risk. This study suggests that some of the sound is being filtered out.

It also suggests that mothers who play music to their unborn children should chose something with a lot of bass if they want their babies to hear the notes. But we're still no nearer to knowing whether the practice gives them a head start in life, says Alexandra Lamont, who studies early development at Keele University, UK. "People try to 'teach' their babies by playing them music in the womb, but there's little evidence to suggest that it's advantageous," she says.
 
 
References
Smith, S. L., Gerhardt, K. J., Griffiths, S. K., Huang, X. & Abrams, R. M. Intelligibility of sentences recorded from the uterus of a pregnant ewe and from the fetal inner ear. Audiology and Neuro Otology, 8, 347 - 353, doi:10.1159/000073519 (2003).|Article|