Oct. 19 (UPI) -- New research suggests dogs make a wider variety of facial expressions when their owners or companions are paying attention to them.
When researchers at the University of Portsmouth studied the interactions between dogs and owners, they found canines were more expressive when their human companion was looking at them.
The study -- published this week in the journal Scientific Reports -- suggests a dog's facial expressions are more than just the simple byproduct of a dog's mood but an attempt to communicate.
"We can now be confident that the production of facial expressions made by dogs are dependent on the attention state of their audience and are not just a result of dogs being excited," Juliane Kaminski, researcher at Portsmouth's Dog Cognition Center, said in a news release. "In our study they produced far more expressions when someone was watching, but seeing food treats did not have the same effect."
"The findings appear to support evidence dogs are sensitive to humans' attention and that expressions are potentially active attempts to communicate, not simple emotional displays," Kaminski added.
Biologists have mostly operated under the assumption that the majority of animal facial expressions are involuntary, but the latest research suggests otherwise.
Kaminski acknowledged that the flexibility of canine facial expression may be a result of domestication. But it's also possible animals boast more expressive agency than given credit for.
The study included 24 dogs of various breeds. Each dog's face was filmed while walking and interacting with its owner. Scientists modified facial movement tracking technology called FACS -- originally designed for human faces -- to record changes in each dog's expression.
"DogFACS captures movements from all the different muscles in the canine face, many of which are capable of producing very subtle and brief facial movements," said researcher Bridget Waller.
Researchers say their findings don't yet reveal whether or not dogs have the capacity to judge another being's mental state, or whether communicative responses are learned or hard-wired reactions. The most common expression during the experiment was the widening of the eyes, or "puppy dog eyes."
The expression most closely resembles a look of sadness among humans, and previous research has shown humans react more emphatically to dogs with puppy dog eyes.
Are dogs having a conversation with their owners, or have they learned new and sophisticated ways to get what they want? To answer that question, researchers say more work in necessary.