Like humans, dogs -- who generally seem to be cheerful, happy-go-lucky characters, so you might expect that most would have an optimistic outlook on life -- can be distinctly pessimistic, according to a recent study.

Optimistic canines have a distinctly sunnier outlook on life, while pessimistic pups are likely to expect the worst.

"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," researcher Dr. Melissa Starling said in a statement.

For the study, dogs were taught to associate two different sounds (two octaves apart) with whether they would get the preferred reward of milk or instead get the same amount of water. Once the dogs have learnt the discrimination task, they are presented with "ambiguous" tones.

If dogs respond after ambiguous tones, it shows that they expect good things will happen to them, and they are called optimistic. They can show how optimistic they are by which tones they respond to. A very optimistic dog may even respond to tones that sound more like those played before water is 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," Starling said.

Based on the findings, a dog with an optimistic personality expects more good things to happen, and less bad things. The dog will take risks and gain access to rewards. The dog isn't bothered by minor setbacks.

A pessimistic dog expects less good things to happen and more bad things. This may make the dog cautious and risk averse. They may readily give up when things don't go their way, because minor setbacks distress them.

"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," Starling added.

The findings, which were published in PLOS, could help working dog trainers select dogs best suited to working roles.

"If we knew how optimistic or pessimistic the best candidates for a working role are, we could test dogs' optimism early and identify good candidates for training for that role," Starling said.