HENRY

Erica Cartmill and Richard Byrne announce in today’s Current Biology, that Orangutans Modify Their Gestural Signaling According to Their Audience’s Comprehension (doi:10.1016/j.cub.2007.06.069):

When people are not fully understood, they persist with attempts to communicate, elaborating their speech in order to better convey their meaning. We investigated whether captive orangutans (Pongo pygmaeus and Pongo abelii) would use analogous communicative strategies in signaling to a human experimenter, and whether they could distinguish different degrees of misunderstanding.

To do this, the Orangutans were offered two types of food - one which they really like, and one which is less tasty, and were given the one they gestured for. All the gestures were directed towards the tasty food, whilst the experimenter sat silently for 30 seconds, before giving the orangutan some food.

Some of the time, the experimenter gave the apes all of the tasty food they wanted, so that the gestural communication was successful: the orang communicated that they wanted the tasty food, and received the tasty food too. In other cases, the experimenter gave out a mix of half the tasty food, and half the less-tasty food (partially successful communication), or gave them all the disliked food (a complete failure to communicate effectively).

The types of gestures from the orangutans were quite varied:

The fascinating thing here, is that the Orangs responded differently to each condition. Once they communicated successfully, and gotten the food, the gestures stopped almost completely. In contrast, when they were partially successful, they tended to repeat the original gesture, but when communication was unsuccessful (and they got the yuck-food), they changed to a different gesture.

These results suggest that the Orangutans are actively monitoring their gestures with regard to their effectiveness at communicating: if the gesture only partially worked, they repeated it (stupid humans), or if it completely failed, they tried a different gesture.

The authors conclude that:

Although the communication sequences of the orangutans are perhaps not as sophisticated, they nonetheless accomplish the same objectives. By maximizing efficiency at searching for an understood signal and homing in on those that achieve partial success, orangutans are able to overcome misunderstandings. In the absence of a shared lexicon, one way of arriving at a shared meaning is to adopt a charades-like strategy, transmitting not only the content of the intended message but also a signal indicating how well you have been understood.

If the recipient can use this information, then the signaler and recipient will be able to arrive at a common understanding much faster. This strategy offers one possible pathway toward constructing a shared lexicon from learned or ritualized signals. Investigations into the structures of intentional communication by apes may therefore provide insight into the prelinguistic devices that helped construct the very earliest forms of hominid language.

Posted on August 7th, 2007 by Simon Greenhill