Scientists at the Messerli Research Institute's Clever Dog Lab in Vienna trained dogs to associate pictures of happy or angry faces with a reward.

 

In a subsequent test, the scientists showed the dogs images of human faces they had not seen in their training.

 

This suggested that dogs could spot the difference between the expressions.

 

"The main focus [of our research] is the big question of communication," lead researcher Prof Ludwig Huber said.

 

"How is it that dogs are so adapted to humans, and what's happened during the process of domestication¹?"

 

The scientists repeatedly showed 20 dogs half pictures - either the lower mouth region or the upper eye area - of happy or angry human faces.

 

Half the dogs received a treat when they touched an angry face with their nose. The other half were rewarded for touching² happy faces.

 

Just over half the dogs learned the task well enough to be tested, and there were then a number of different tests to find out if they could tell the difference solely³ on the basis of facial expression.

 

"[In one test condition], we showed them new faces - faces they've never seen before," Prof Huber told BBC News.

 

"In another, we showed them different parts of the faces."

 

Showing dogs the opposite half of the face to the half they had learned to recognise in their training, showed they could "transfer their knowledge" of human facial expressions.

 

"So, for example, in the training, they see the mouth region of the happy face," said Prof Huber, "and they associate that with what the eyes would look like."

 

This study, published in the journal Current Biology, is part of a larger project studying how humans and their canine⁴ companions interact.

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