Despite their constant grinning, research shows that some dogs are distinctly more pessimistic than others.

Given that the biggest daily challenge in many dogs’ life involves the choice of bathroom location, it would be easy to assume that they choose to see a glass half full, but a new study from the University of Sydney shows otherwise.

“This research is exciting because it measures positive and negative emotional states in dogs objectively and non-invasively. It offers researchers and dog owners an insight into the outlook of dogs and how that changes,” said Dr Melissa Starling, from the Faculty of Veterinary Science.

Dr Starling’s PhD research findings are published in PLOS today.

“Finding out as accurately as possible whether a particular dog is optimistic or pessimistic is particularly helpful in the context of working and service dogs and has important implications for animal welfare.”

Dogs were taught to associate two different sounds (two octaves apart) with whether they would get the preferred reward of milk or instead get an equal amount of water.

Once the dogs learned the discrimination task, they were presented with ‘ambiguous’ tones.

If the dogs responded after ambiguous tones, research took it to show that they expect good things will happen to them, and they are deemed optimistic.

It was even possible to show how optimistic they were by which tones they respond to.

A very optimistic dog appeared to respond to tones that sounded more like those played before water was offered.

“Of the dogs we tested we found more were optimistic than pessimistic but it is too early to say if that is true of the general dog population,” said Dr Starling.

Dr Starling has been working with Assistance Dogs Australia, a charity organisation that provides service and companion dogs to people with disabilities, to investigate whether an optimism measure could aid in selecting suitable candidates for training.

“This research has the potential to completely remodel how animal welfare is assessed,” she said.

“If we know how optimistic or pessimistic an animal usually is, it's possible to track changes in that optimism that will indicate when it is in a more positive or negative emotional state than usual.”