This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Imagine that you walk into a room, where three people are sitting, facing you. Their faces are oriented towards you, but all three of them have their eyes directed towards the left side of the room. You would probably follow their gaze to the point where they were looking (if you weren't too unnerved to take your eyes off these odd people).
As a social species, we are particularly cued in to social cues like following others' gazes. However, we're not the only animals that follow the gazes of members of our species: great apes, monkeys, lemurs, dogs, goats, birds and even tortoises follow each other's gazes too. However, we don't all follow gazes to the same extent. One species of macaque monkey (the stumptailed macaque) follows gazes a lot more than other macaque species, bonobos do it more than chimpanzees and human children follow gazes a lot more than other great ape species do.
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Species also differ in their understanding of what the other animal is looking at. For example, if we saw a person gazing at a point, and between them and this point was a barrier, whether the barrier was solid or transparent would affect how far we followed their gaze. This is because we imagine ourselves in their physical position and what they might be able to see. Bonobos and chimpanzees can also do this, but not the orang-utan. Like us, great apes and old world monkeys also will follow a gaze, but then look back at the individual gazing if they don't see what the individual is gazing at ('are you going crazy or am I just not seeing what you're seeing?'). Capuchin and spider monkeys don't seem to do this.
So, even though a lot of animals are capable of following the gazes of others, there is a lot of variation in the extent and flexibility of this behaviour. A recent study looked to see whether chimpanzees, bonobos, orang-utans and humans would be more likely to follow their own species' gazes than another species.
To do this, the researchers showed the test subjects videos of either an animal of the same species or of a different species (the 'model') looking in a particular direction. The scientists then looked to see if the animal watching the video looked in the same direction as the model. To more easily see where the non-human primates' gazes fell, the researchers wanted to keep their heads in a particular position (facing straight ahead). To do this, they gave the animals a straw that they could suck on to get grape juice. They filmed these animals, and then used computer software that tracked which direction the individuals' eyes moved.
Image above: a) the participants of the study, sucking on grape juice to keep their heads still. b) the models of the study, that the participants watched on video
All four primates (the chimpanzees, bonobos, orang-utans and humans) followed the gaze of the model in the video when they were the same species as themselves. This is not surprising, as all of these species are known to follow gazes.
However, while human adults, orang-utans and bonobos all would follow the gaze of both their own species, and of a different species, human infants and chimpanzees only followed the gaze of their own species. Why might this be? Well, the human infants and chimps were particularly inattentive to the videos being shown to them. Therefore, it's likely that they didn't follow the gaze of the video demonstrator not because they were incapable of it, but simply because they lacked the motivation to do so. Given this lower level of motivation, it is only the more salient stimulus of seeing their own species on the video that gets them to pay attention.
Photo Credits
Man's gaze: Llima Orosa
Stump-tailed macaque: Thomas Quine
Experimental photos taken from Kano & Call 2014
Reference
Kano, F., & Call, J. (2014). Cross-species variation in gaze following and conspecific preference among great apes, human infants and adults. Animal Behaviour, 91, 136-149.