Most dog owners have seen their dogs showing what we consider to be signs of jealousy. In fact, dog trainers have long been using jealousy as a training tool by removing unresponsive dogs during training, allowing the dogs to watch their handlers working another dog close by. This appears to be a great motivator for many dogs. But do dogs really experience the emotion of jealousy? Researchers have argued about whether dogs can become jealous since this requires complex cognition.

In a 2014 University of California, San Diego study published in PLOS ONE, researchers Dr. Caroline Prouvost and Dr. Christine Harris addressed this topic. In this study, dog owners had to recount stories of when their dogs were "jealous." Most of the dog owners described similar characteristics of jealousy that their dogs had displayed in the past. When their dogs were jealous, they would engage in attention-seeking behaviors like pressing up against their owners, or going in between the owner and the person who was the object of the jealousy. They would bark, growl, whine and sometimes become aggressive. Some dog owners also claimed that their dogs felt guilty after being jealous, yet researchers say there is no empirical data that demonstrates a dogs guilt.

According to the new research paper in PLOS ONE, Dr. Harris and Dr. Prouvost modified a test used to assess jealousy in six-month-old babies. This is the first test used on dogs to measure jealousy. Thirty-six dogs participated in this study for three different tests. These dogs were videotaped inside their homes by the researchers who recorded the dog's owners ignoring their dogs and focusing on a stuffed, animated dog or jack-o-lantern pail. In this scenario, the dog owners had to treat the objects like real dogs. They petted and talked to them affectionately, pretending that they were real dogs. Next, the owners had to read a pop-up book that played melodies to the pretend dog. Two independent researchers then rated the videos for different forms of aggression and other behaviors that are associated with jealousy. 

None of the dog owners were aware of what was being tested, and did not know what the hypothesis of the experiment was. In that way, they could not influence their dog's reactions during testing. All testing was videotaped. The owner then completed a questionnaire, and could interact freely between testing so that there would be a limited amount of carryover effects from the earlier tests. Each test took a minute.

The researchers used a stuffed dog that looked real, barked, whined and wagged its tail for eight seconds after a button was pressed. The participants were told to ignore their own dogs and to focus on the stuffed dog. They also had to do the same thing with a jack-o-lantern and a pop-up book that played songs.