Researchers have discovered what pet lovers have known for a long time - dogs are incredibly astute at reading human emotions. It's not merely a matter of recognising facial expressions, but an assessment of a mood based on a combination of sensory information, according to scientists. It's an ability until now only identified in primates and humans.

"It has been a long-standing debate whether dogs can recognise human emotions," Professor Daniel Mills of the UK's University of Lincoln told Medical News Today. "Many dog owners report anecdotally that their pets seem highly sensitive to the moods of human family members. Our findings are the first to show that dogs truly recognise emotions in humans and other dogs."

Dogs are capable of integrating "two different sources of sensory information into a coherent perception of emotion," wrote co-author Kun Guo from the School of Psychology at Lincoln. "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."

For the study by the professors, written up in Biology Letters, researchers showed 17 domestic dogs pictures of both humans and other dogs displaying positive or negative emotional expressions, and played positive and negative audio clips from unfamiliar people and dogs.

When the picture and sound "matched" — that is, they were both negative or both positive — the dogs recognized that and stared longer at the pictures. The findings indicated that dogs are capable of combining different sensory information to form a mental portrayal of positive and negative emotional states of humans and canines, noted the scientists.

Dogs' uncanny ability to read emotions and, presumably, respond appropriately would have provided evolutionary advances as dogs threw in their lot with humans. "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," said Mills.