Dogs combine sensory information to identify the emotional states of both dogs and humans, say researchers.
Previous research claims that dogs' ability to differentiate between human emotions is down to "associate behavior" - in which they link certain emotional states to facial expressions or other cues that they have learned.
But according to study coauthor Prof. Daniel Mills - of the School of Life Sciences at the UK's University of Lincoln - and colleagues, their research challenges this theory.
"It has been a long-standing debate whether dogs can recognize human emotions," notes Prof. Mills. "Many dog owners report anecdotally that their pets seem highly sensitive to the moods of human family members."
"However, there is an important difference between associative behavior, such as learning to respond appropriately to an angry voice, and recognizing a range of very different cues that go together to indicate emotional arousal in another," he adds.
"Our findings are the first to show that dogs truly recognize emotions in humans and other dogs."
Dogs combine sensory info to form mental image of emotional states
For their study, published in the journal Biology Letters, the team showed 17 domestic dogs pictures of both humans and other dogs displaying positive (happy or playful) or negative (angry or aggressive) emotional expressions.
Alongside the picture presentation, the researchers also played positive or negative audio clips (voices or barks) from unfamiliar human and canine subjects.
The team found that when the dogs were shown a picture that matched the emotional state of an audio clip - for example, if an angry voice matched an angry facial expression - they spent much longer looking at it. This was the case for both human and canine pictures and audio clips.
The team says their findings indicate that dogs combine different sensory information to form a mental portrayal of the positive and negative emotional states of humans and canines.
Study coauthor Dr. Kun Guo, from the School of Psychology at Lincoln, explains:
"Our study shows that dogs have the ability to integrate two different sources of sensory information into a coherent perception of emotion in both humans and dogs.
To do so requires a system of internal categorization of emotional states. This cognitive ability has until now only been evidenced in primates and the capacity to do this across species only seen in humans."
Prof. Mills notes that the dogs in the study had no prior training and were unfamiliar with the human and canine subjects in the pictures and audio clips, suggesting that dogs' ability to draw on different sources of sensory information may be inherent.
"As a highly social species, such a tool would have been advantageous, and the detection of emotion in humans may even have been selected for over generations of domestication by us," he adds.
Last year, Medical News Today reported on a study that claimed to explain why we are unable to resist dogs' famous "puppy dog eyes" glare.