Mime artists: The interactions are likened to a game of charades because the orangutans are passing information back to the researchers to indicate whether they are close to – or very far from – understanding.
Credit: Erica Cartmill/Durrell Wildlife Conservation Trust
SYDNEY: Orangutans can distinguish between when they are partially or completely misunderstood during communication, and modify gestures to get their point across.
A new study reports that the great apes use gestures to communicate, and rely on much the same strategy that people employ during a game of charades.
"We were surprised that the orangutans' responses so clearly signalled their assessment of the audience's comprehension," said Richard Byrne, evolutionary psychologist at the University of St. Andrews in Fife, Scotland, co-author of the study published today in the journal Current Biology.
"Looking at the tapes of the animal's responses, you can easily work out whether the orangutan thinks it has been fully, partially, or not understood – without seeing what went before," said Byrne.
Communicating intention
Though orangutans are already known to react when people are observing them, researchers didn't know whether they could communicate their intentions to humans with gestures, as chimpanzees do.
So the researchers set out to test if the apes would modify their behaviour depending on whether or not people appeared to understand their intentions.
In experiments with six captive, female orangutans at the Durrell Wildlife Conservation Trust on the British island of Jersey, they presented two food options, one desirable (a banana or bread), one unwanted (a leek or celery).
The orangutans used gestures to indicate their goal (i.e. give me the entire more tempting snack) to the researcher and received one of three responses. The first outcome was that they were understood and received their food, attaining their goal. Under the next two outcomes, initial gestures appeared to be misunderstood by the researcher, resulting in the apes receiving the less tempting snack or only part of the desired one.
When the goal was met, on almost all occasions, the primates would cease to gesture. When the goal was not met, a second attempt to communicate intention was recorded; but with distinctly different gestures representing an alternative strategy to communicate and depending on the degree of understanding indicated by the researcher.
Theory of mind
"The orangutans made a clear distinction between total misunderstanding, when they tended to give up on the signals they'd used already and use new, but equivalent, ones to get the idea across, and partial misunderstanding, when they tended to repeat the signals that had already partly worked, keeping at it with vigour," said psychologist and study co-author Erica Cartmill also of St. Andrews University.
"The result is that understanding can be achieved more quickly," She added.
The researchers liken the interaction to a game of charades because the orangutans are passing information back to the audience to indicate whether they were close to, or very far from, understanding in order to point them in the right direction.
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A 30 second clip from one of the trials. A 42-year-old Sumatran orangutan, Gina (and her infant Jaya), communicating with researcher Gordon Hunt. The clip ends when Gordon gives Gina half of the desired banana. (Courtesy of Erica Cartmill and the Durrell Wildlife Conservation Trust). div> |
These 'hints' indicate that the apes are tracking the degree to which their gestures are understood, potentially providing insight into non-verbal methods that shaped the earliest forms of human language, said the researchers.
The findings suggest that "the orangutans are to some extent capable of 'theory of mind'" – which is the ability to understand what is going on in the minds of others – commented Michael Corballis, psychologist at the University of Auckland in New Zealand.
Danielle Clode, psychologist specialising in animal behaviour at the University of Melbourne, Australia, has reservations about the conclusions of the study, however. "The very simple and powerful explanation is that their results can be explained with operant conditioning where animals learn to repeat behaviours when they are rewarded," she said. "This experiment doesn't require comprehension."
Clode argued that alternative methods would need to be developed to effectively gauge levels of comprehension and understanding.
