PHILADELPHIA (CBS) – The idea that dogs are easy-going, laidback and optimistic might be true, but only for some pups.

According to new research out of Australia’s University of Sydney, some dogs are actually more of the glass half-empty type.

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Researchers say they taught dogs to associate two different sounds two octaves apart with whether they’d get a reward of milk, which was preferable over the same amount of plain old water.

Once the canines learned the discrimination task, the scientists tried the same test with more ambiguous tones.

Apparently, if the dogs responded to the ambiguous tones, it meant they expected a reward. Those dogs were deemed optimistic, and according to the researchers, “a very optimistic dog may even respond to tones that sound more like those played before they were given water.”

On the other hand, a pessimistic dog might be cautious and risk averse, though not necessarily unhappy. Those dogs responded to fewer tones and were more likely to give up on tasks easily.

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“Pessimistic dogs appeared to be much more stressed by failing a task than optimistic dogs. They would whine and pace and avoid repeating the task while the optimistic dogs would appear unfazed and continue,” said Dr Melissa Starling, from the Faculty of Veterinary Science, who conducted the study.

Interestingly, Starling says that her findings could help train service dogs. For instance, a more pessimistic animal would be a better guide dog, since he or she is more risk averse, while an optimistic dog would be better suited to detecting drugs or explosives since those animals tend to be more persistent.

Dr. Starling’s research is published in the journal PLOS One.

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