The trope of a dog bounding to the rescue of a human is a well established one – from the helpful St. Bernard to Lassie – but does it have any scientific backing?

A new study says that yes, our canine companions really do want to rescue us from harm - as long as they know how, that is.

To try and get a clear idea of whether dogs were acting on an impulse to rescue, rather than a desire to get food or simply to make contact with their owners, the researchers ran a series of carefully constructed experiments.

The main tests involved 60 pet dogs, presented with their owner trapped inside a large box, with a lightweight door that could easily be shifted by the pooches.

The dog owners were coached to cry out for help from inside the box in an authentic way.

"About one-third of the dogs rescued their distressed owner, which doesn't sound too impressive on its own, but really is impressive when you take a closer look," says psychologist Joshua Van Bourg, from Arizona State University.

"The key here is that without controlling for each dog's understanding of how to open the box, the proportion of dogs who rescued their owners greatly underestimates the proportion of dogs who wanted to rescue their owners."

In other words, the research suggests more of the canines wanted to rescue their owners, but didn't know how.

In a test where food was dropped into the box in view of the dogs, with no owner present, 19 out of the 60 dogs retrieved the snack – compared with 20 out of 60 for the owners-in-distress tests.

Of those 19 dogs, 16 of them also released their owners from captivity in the other experiment: a hit rate of 84 percent. It seems most canine companions want to help us in times of distress, but they need to know how to be able to do it first.

The researchers took other steps to try and figure out the dogs' motivations. Owners weren't allowed to say their dogs' names – to make sure the dogs weren't just following orders – and a separate test had the owners simply reading a magazine inside the box to compare it with the test where they were in distress.

"During the distress test, the dogs were much more stressed," says Van Bourg.

"When their owner was distressed, they barked more, and they whined more. In fact, there were eight dogs who whined, and they did so during the distress test. Only one other dog whined, and that was for food."

In the test where the owner sat and read in the box, 16 of the dogs opened the door to let the owner out (or to get closer to the owner). The researchers say that just being with their owner is a strong motivation for dogs, but that knowing owners are in distress adds even more urgency.

Some of the tests were repeated too. With repeated distress tests, the dogs' anxiety levels stayed about the same, but with repeated reading tests, the pooches seemed to be less stressed each time around.

That would appear to show "emotional contagion", according to the researchers – where emotions are passed from owner to dog.

The fact almost as many dogs opened the box to get food as to rescue their owners suggests that the two actions are seen as similarly rewarding by the pets.

Of course, we can't read dogs' minds (unfortunately). So to get a better understanding of what's going on and what drives the rescue impulse, further experiments are needed.

"What's fascinating about this study is that it shows that dogs really care about their people," says psychologist Clive Wynne, from Arizona State University. "Even without training, many dogs will try and rescue people who appear to be in distress – and when they fail, we can still see how upset they are."

"The results from the control tests indicate that dogs who fail to rescue their people are unable to understand what to do – it's not that they don't care about their people.

"Next, we want to explore whether the dogs that rescue do so to get close to their people, or whether they would still open the box even if that did not give them the opportunity to come together with their humans."

The research has been published in PLOS One.