updated 10/14/2010 11:17:21 AM ET 2010-10-14T15:17:21

Optimists and pessimists don't only inhabit the human world, dogs may also see the glass -- or, in this case, bowl -- as half full or half empty, determined new research.

The findings suggest that dogs, and probably other animals too, have underlying states of mind, which can affect their judgments and behavior. Pessimistic dogs are more likely to engage in unwanted activities, such as barking, destruction, and toileting when and where they shouldn't.

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"In humans, at least, research shows that 'optimistic' or 'pessimistic' decisions are useful indicators of an individual's emotional state," project leader Michael Mendl told Discovery News. "Happy people tend to be more optimistic. This may also be the case in animals, including dogs."

Mendl, who is head of the Animal Welfare and Behavior research group at Bristol University's School of Clinical Veterinary Science, and his team came to this conclusion after putting 24 male and female dogs, representing different ages, through a few tests.

For the first test, each dog was taken to a room where a researcher interacted with it for 20 minutes. The next day, the researcher did the same thing, but left after just five minutes of interaction. The scientists documented how the dog, when left alone, acted. Some dogs, for example, happily awaited the person's return, while others barked and became anxious.

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Next, the researchers trained the dogs to understand that a bowl on one side of a room was full of yummy food, while a bowl on the other side was empty. The researchers then placed bowls at ambiguous places and observed how quickly the dogs would go to the bowls.

"Dogs that ran fast to these ambiguous locations, as if expecting the positive food reward, were classed as making relatively optimistic decisions," explained Mendl. "Interestingly, these dogs tended to be the ones who also showed least anxiety-like behavior when left alone for a short time."

The findings are published in the latest issue of Current Biology.

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Prior work by this team and others suggests that sheep, monkeys, pigs and a bird (the starling) also appear to either be optimists or pessimists. Since genetics may be involved, it's possible that, for dogs, certain breeds are more prone to judging events more pessimistically than others, but more research is needed to identify those breeds.

According to Samantha Gaines, deputy head of the Companion Animals Department from the Royal Society for the Prevention of Cruelty to Animals, "Many dogs are relinquished each year because they show separation-related behavior."

She added, "Some owners think that dogs showing anxious behavior in response to separation are fine, and do not seek treatment for their pets.

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This research suggests that at least some of these dogs may have underlying negative emotional states.

Mendl points out that many dog owners probably don't even realize that their pet may be suffering from the blues.

This condition could be similar to human depression. Probable causes range from genetic predisposition to life experiences and other factors. Even if owners do recognize such a problem in their dogs, Mendl thinks they may be unaware that help is available.

Therapy "might involve teaching dogs to be less dependent on owner attention, and getting them progressively more relaxed about being left by their owners," he said. "Some severe cases may also need drug therapy in addition to behavior therapy."

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© 2012 Discovery Channel


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