What makes yawning so contagious? Empathy, as it turns out, causes us to respond to a friend’s boredom. Children as young as two can display the basic capacity to understand how others feel, and respond accordingly, and several studies have indicated that this trait is so ingrained that we even respond to computer-generated animations, cartoons, and puppets.

Empathy isn’t only limited to humans. The chimpanzee and many of our other primate relatives are fully capable of processing complex emotions and behaviors. Chimps can also learn new abilities by watching their peers' actions and copying them. Matthew Campbell, a post-doctoral fellow at Emory University who studies primate behavior, and his colleagues wanted to see whether chimps identify with computer animations the same way they do with expressions from real-life animals. The (perhaps) surprising answer: yes, they do. The results are reported in the Proceedings of the Royal Society B.

You may be wondering why scientists are so interested in finding out whether or not chimps respond to computer-animated stimuli. It turns out to be a practicality issue. To study the full range of behaviors in primates, researchers need to be able to replicate them, which they do by filming real-life examples. But therein lies the problem.

Scientists need to have reproducibility in their experiments so that other scientists, working independently, can repeat them later on. Few things are less reproducible than complex animal behaviors. Scientists are also interested in obtaining examples of "impossible" behaviors, which the authors define as "behaviors not in the repertoire of the subjects or species." While these could yield crucial new insights into animal cognition, emotion, and behavior, they are, by definition, impossible to generate, much less replicate.

A computer program that recreates behaviors and expressions would therefore allow researchers to circumvent these nagging issues. A study done last year concluded that chimps interpret computer animations in the same way that they did real images, but Campbell and his co-authors wanted to determine whether the chimps would also respond to the animations. They chose to test their response to animated yawns for two reasons: contagious yawning is involuntary, and the behavior has been observed in chimps before.

The authors made 24 chimps watch three-dimensional computer animations of chimpanzees yawning or controls where they were just moving their mouths. The soundless animations were presented from several different viewing angles and perspectives and lasted 10 seconds each. The 10 second animation clips were then assembled into 15 minute long yawn and control videos.

To put the chimps at ease while viewing the videos, they were tested in pairs chosen for compatibility. Half of the subjects watched the yawn video first while the other half started with the control video. Their responses to the animations were evaluated for the number of yawns and the amount of time they spent watching the monitor.

Overall, the subjects yawned much more often in response to the yawn video than they did to the control video. Contagious yawning in chimps, as in humans, thus seems to occur as an act of subconscious identification rather than as an act of purposeful imitation. However, they spent roughly equal amounts of time looking at each video, suggesting that one stimulus was not more compelling than other.

Repeated viewings didn't change the number of yawns induced, so the authors concluded that boredom on the part of the chimps did not bias their results. (The number of yawns during the control video did go up as its novelty wore off, though.)

The authors are currently investigating whether animated yawns produce a greater or lesser response than real-life yawns. In the next phase of their experiment, they also plan on separating the chimps before making them watch the videos in order to ensure that one isn't simply imitating another's actions.

The obvious way to expand on these results is to determine how many other animals, primates or otherwise, respond to computer animations. If this technique can be applied to a range of other mammals, it could open the door to many innovative experiments in cognitive and behavioral science, and teach us something new about ourselves in the process.

Proc. R. Soc. B, 2009. DOI: 10.1098/rspb.2009.1087

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