Dogs can pick up emotional cues from another dog by watching the direction of its wagging tail, a new study suggests.
In a series of lab experiments, dogs got anxious when they saw an image of a dog wagging its tail to its left side. But when they saw a dog wagging its tail to its right side, they stayed relaxed.
This isn't the first time scientists have shown that the direction of a wagging tail can be linked to doggy emotions. In a previous study, Giorgio Vallortigara of the University of Trento in Italy and his colleagues showed that dogs tended to wag to their right side when seeing something friendly, like their owners. Seeing something threatening, like a dominant unfamiliar dog, made them wag more to their left side.
That study made the scientists wonder if other dogs might actually watch another dog's tail wagging and use its direction as a clue to figure out whether that dog might be a potential friend or foe.
"The question was at this point: Does asymmetric tail wagging convey meaning to other dogs?" says Vallortigara.
To find out, they had 43 dogs wear some little vests that would monitor their heart rates. Then they had the dogs watch some special images of dogs that were designed to remove all stimuli except the wagging tail.
Some of the tested dogs saw a video that showed a silhouette of a dog, while others saw a manipulated image of a real dog. In both cases, the only thing that moved in the image was the tail.
When dogs saw a dog image or silhouette wagging its tail to its right side, they stayed relaxed. But when they saw a dog wagging its tail to its left side, their hearts began to race and they looked anxious. The results are reported in the journal Current Biology.
Tom Reimchen, a biologist at the University of Victoria, calls this an "elegant" study. He says there's been a lot of work showing asymmetries in animals' bodies, but "what has not been found is whether there is information that others can gain from that type of laterality," says Reimchen. "And so that's why I think their current paper is very, very interesting and important."
Reimchen and his colleagues had previously tested how dogs would respond to asymmetrical tail-wagging by videotaping dogs as they approached a robotic dog with a remote-controlled tail.
They found that the number of stops that a dog would make when approaching the robodog was higher when tail-wagging was to the right. It may be that dogs were attracted to this apparently friendly tail-wagging, but were confused by the immobile robot's lack of other signals that might convey friendship.
Reimchen says that once people become aware of left vs. right in terms of communicating information, "it suddenly opens up a whole new range of type of questions and the type of observations you're making that you before sort of completely overlooked. These animals are probably far more cognizant of those subtle differences than we would have suspected before."
And while it would be a lot harder for people to spot asymmetrical tail-wagging than it is for dogs, scientists say there could be some practical reasons to try to understand left-right differences in these animals. "These results suggest that dogs have perceptual and attentional asymmetries," says Vallortigara. "So for example, if you are going to visit a dog, if you are vet, there will be probably a side which is better with respect to the probability to evoke a more friendship response or to evoke a more aggressive response."
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Here's something to contemplate on a Friday. When dogs wag their tails, they sometimes wag more on the right side of their bodies, and other times more on the left. It turns out which side the tail is wagging is actually a clue to the dog's emotional state. And a new study shows that other dogs react to the direction of the wag, as NPR's Nell Greenfieldboyce reports.
NELL GREENFIELDBOYCE, BYLINE: Giorgio Vallortigara is a biologist at the University of Trento in Italy. And he says the point of his experiments is not just to understand dogs.
GIORGIO VALLORTIGARA: I have a dog, actually. And I love dogs. But in this particular case, the reason was scientific interest.
GREENFIELDBOYCE: Vallortigara studies how asymmetries in the brain lead to left-right differences in how animals behave. Years ago, his research team did an experiment that showed one example in dogs. Dogs that saw friendly things, like their owners, wagged their tails more to the right side. Dogs that saw threatening things - like an aggressive, unfamiliar dog - had more wagging to the left.
Vallortigara says this seems to be related to how those different stimuli got processed in the dogs' asymmetrical brains, but it made him wonder.
VALLORTIGARA: The question was, at this point: Does asymmetric tail wagging convey meaning to other dogs?
GREENFIELDBOYCE: To find out, the researchers had 43 dogs come to a lab. The dogs wore some little vests that monitored their heart rates. And these dogs watched videos. The videos showed either a natural-looking dog, or just a silhouette of a dog, with the tail wagging to the right or to the left.
It turns out, the dogs did respond to the direction of the wagging. When the video dog wags to its left - the kind of wagging that's linked to negative emotions - the watching dogs got anxious, and their hearts began to race. If the video dog wagged to its right, the watching dogs stayed relaxed. The results are reported in the journal "Current Biology."
TOM REIMCHEN: I really felt that their paper was elegant.
GREENFIELDBOYCE: Tom Reimchen is a biologist at the University of Victoria, in Canada. He once tested whether dogs paid attention to the direction of another dog's tail wagging, by going to a park and setting up a robotic dog with a remote-controlled tail.
REIMCHEN: Our robo-dog is so realistic, it does, actually, trick many, many dogs until they finally get to it, and they realize that they've been duped.
GREENFIELDBOYCE: His group found that when the robo-dog wagged to its right, other dogs would stop and pause more often as they approached. It's not clear exactly why, since right wagging should be a more positive signal. But Reimchen says the important thing is that, like this new study, it shows that animals seem to get information about each other by watching for left versus right.
Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.