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Dogs can tell when you're happy or sad, study finds

Dog owners tend to feel like their pets understand them. A new study shows that might in fact be the case.

Animal behavior experts and psychologists from the University of Lincoln, in the U.K., and University of Sao Paulo, Brazil, presented 17 domestic dogs of various breeds with images of human or dog faces showing expressions of either happiness or sadness. The sound of a bark or a human voice in Portuguese (a language that none of the dogs knew) was also played.

Video recordings of the dogs showed that they looked much longer at the picture when the facial expression matched the tone of voice being played, for both humans and canines.

The researchers say the results, published in the journal Biology Letters, reveal that dogs can interpret the facial and vocal expressions of another species, an abstract form of thinking that has only been seen in humans.

Examples of stimuli used in the study: faces (human happy versus angry, dog playful versus aggressive) and their correspondent vocalizations. Natalia Albuquerque, et al.

"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," Dr. Kun Guo, from the University of Lincoln's School of Psychology, said in a press release. "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."

The dogs in the trial did not receive any training prior to the study and were not familiar with the subjects in the images or the sounds. "This suggests that dogs' ability to combine emotional cues may be intrinsic," said co-author Prof. Daniel Mills, from the School of Life Sciences at the University of Lincoln. "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."

The researchers say the discovery could be valuable for pet owners and those who work with the animals. "Studying dog behavior and cognition allows us to better understand who dogs are and what they need, why we interact and relate to these animals and why they are so important to us," lead author Natalia Albuquerque, from the School of Life Sciences at the University of Lincoln, told CBS News in an email. "Also, this is a fundamental knowledge towards a better and more functional relationship with them and to develop the techniques, routines and procedures when having them as assistants in different therapies, for example."

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