Fetus Knows Mom's Voice
NEW YORK (Reuters Health) - New
study findings suggest that shortly before birth, a fetus may
be able to distinguish mom's voice from others.
U.S. researchers found that heart
rate in full-term fetuses increased when a recording of their
mothers' voices was played, but decreased in response to the voice
of a female stranger.
This shows that the fetus can distinguish
between the voices of its mother and other women before it is
even born, study author Dr. Barbara S. Kisilevsky of Queen's University
in Canada told Reuters Health.
"It is not the increased heart
rate per se, but the different ways in which the fetuses responded
to the two voices ... that tells us that the fetus had to recognize
its own mother's voice," she said. "If not, then the response
to both voices would have been the same."
These results add to a body of
research suggesting that biology prepares the fetus to bond to
its mother after birth and take on the daunting task of learning
language, Kisilevsky noted.
Furthermore, showing that a fetus
can distinguish its mother's voice adds credence to the theory
that both genes and experience help a fetus understand speech,
because the tendency to respond differently to different voices
"had to occur through experience," Kisilevsky said.
During the study, reported in the
May issue of the journal Psychological Science, Kisilevsky and
her colleagues played a tape recording through speakers held around
10 centimeters over the mothers' abdomens.
The tapes consisted of two minutes
of silence followed by two minutes of either the mother or a female
stranger reading the same poem, then two more minutes of silence.
On average, the fetuses had spent
about 38 weeks in the womb, and so were full-term. Thirty fetuses
were exposed to tapes of their mothers speaking, and another 30
the voices of a female stranger.
Although mothers' voices did not
appear to elicit significantly more body movement in the fetuses
than did the voices of female strangers, fetal heart rate increased
when listening to their mothers, and appeared to decrease in response
to a recording of a female stranger.
In terms of why a stranger's voice
might lower a fetus's heart rate, Kisilevsky said that a decrease
in heart rate is often a sign of attention, and the fetus may
have paid more attention to a voice it didn't recognize.
"I think it already knew its mother's
voice, and was now learning about other voices," she said.
SOURCE: Psychological Science 2003;14:220-224.
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