New York Times
July 1, 2003
Monkey See, Monkey Speak: Facial Expressions as a Guide to Speech
By HENRY FOUNTAIN
Scientists have long known that there is more to speech perception than meets
the ear. Humans, even infants who cannot yet speak, pick up visual cues from
the movement of the lips and other parts of the face to help understand what it
is they are hearing.
Now there is evidence that this ability may go back a long way. Researchers in
Germany say they have found that rhesus monkeys can also combine visual and
auditory information to perceive vocal signals, suggesting that the ability had
some kind of evolutionary precursor before humans and other primates diverged
millions of years ago.
The researchers, Dr. Asif A. Ghazanfar and Dr. Nikos K. Logothetis of the Max
Planck Institute for Biological Cybernetics in Tübingen, tested monkeys by
showing them side-by-side video images of another monkey making two sounds,
while playing a soundtrack of just one of the sounds. Time after time, the test
monkeys were able to match the sound with the correct video image. The research
was reported in the current issue of the journal Nature.
"We know that for human speech perception, when you communicate one on one with
someone, you glean a lot of information not only from sound, but from facial
expressions," Dr. Ghazanfar said. But with other animals, he said, "we didn't
know if perceivers use that multimodal means of perception as well."
The experiment is very similar to the kind that has been done with infants as
young as 18 to 20 weeks to show that even at a prelinguistic age, they use
facial expressions as an aid to perceiving speech.
But Dr. Ghazanfar said such studies had not been done on other animals,
particularly closely related primates.