Dogs can 'read emotion' in faces

Dogs have a special ability that really marks them out as man's best friend, scientists have discovered.

They appear to read emotion in human faces in just the same way people do. It may be evidence that they can see at a glance if we are happy, sad, pleased or angry.

When humans look at a new face their eyes tend to wander left, falling on the right hand side of the person's face first. This "left gaze bias" only occurs when we encounter faces and does not apply any other time, such as when inspecting animals or inanimate objects.

A possible reason for the tendency is that the right side of the human face is better at expressing emotional state.

Researchers at the University of Lincoln have now shown that pet dogs also exhibit "left gaze bias", but only when looking at human faces. No other animal has been known to display this behaviour before.

A team led by Dr Kun Guo showed 17 dogs images of human, dog and monkey faces as well as inanimate objects. Film of the dogs' eye and head movement revealed a strong left gaze bias when the animals were presented with human faces. But this did not occur when they were shown other images, including those of dogs.

New Scientist magazine reported: "Guo suggests that over thousands of generations of association with humans, dogs may have evolved the left gaze bias as a way to gauge our emotions."

Surprisingly, when the dogs in the study were shown an upside-down human face, they still looked left. In contrast, humans lose their left gaze bias altogether when shown an inverted face.

This may be because the right side of a dog's brain, which processes information from the left visual field, is better adapted to interpreting human facial emotion than the left side, the scientists believe.

Whether or not a "left gaze bias" means that dogs really do read human emotions remains to be tested. But a follow up study showed that angry human faces induce a much stronger left gaze bias in dogs than neutral or happy faces.