Most humans believe their dog’s wildly wagging tail is the key indicator of recognition of its owner; however, there may be more subtle and involuntary signals which even more quickly differentiate a dog’s bond to a particular human.
A new study has found that dogs use involuntary facial expressions that can be quickly decoded to show they are happy to see their owners, reports Business Standards. Japanese researchers tracked changes in the faces of dogs in the moments after meeting a stranger for the first time or being reunited with their owners and found that subtle physical reactions convey their emotional reaction within half a second.
"Ownership is a significant social factor for dogs. This suggests that human-dog bonding relationships have a biological basis," says Dr Miho Nagasawa, from the department of animal science at Azabu University in Sagamihara, Japan.
When the animals were introduced to someone they had never met before, they moved their left ear back slightly. If presented with an object they didn't like--such as pair nail clippers--the animals moved their right ear instead.
But the canines tested tended to move their left eyebrow upwards around half a second after seeing their owner.
The researchers suggest that the subtle changes on different sides of the dogs' face are a reflection of activity in key parts of the brain that control emotions.
The study was conducted by placing 12 dogs in a room divided by a partition with black curtains that opened briefly to all the dogs to glimpse what was on the other side.
Colored tags were placed on the dog's faces to allow a high speed camera to track the movement of their features.
When the curtain opened, their owner, a stranger, a toy or an item they did not like was on the other side, allowing the researchers to record their response.
They found that the dogs moved their eyebrows upwards whenever they saw someone behind the screen, but far more when it was their owner, particularly on the left side. “Eyebrow movement might indicate a visible response whereby dogs attempted to look at their owners more intently," Nagasawa said.
The researchers also believe it could be because the animals were experiencing conflicted emotions - joy at seeing their owner but sadness at not being able to reach them through the partition.
Dogs are highly social and communicate using an abundant array of facial expressions, Dr. Nagasawa states, “These communication methods might play an important role in their communication with humans.”
The study is published in the journal Behavioural Processes.