Dogs are more interested in humans than they are in objects, European researchers say. Their attention level changes throughout their lives just as in humans.

Scientists at Vienna's University of Veterinary Medicine say that a large part of why dogs are man's best friend, is that they adjust so well with our lifestyles.

Dogs have personalities, are aware and have high levels of learning or training ability. But to learn or be trained, they must have certain levels of concentration and attention, the researchers said.

However, just as in humans, that attentiveness changes over the span of a dog's life.

Study leader Lisa Wallis and colleagues observed more than a hundred Border Collies with ages varying from 6 months to 14 years, in a laboratory setting to investigate their attentiveness as they age.

In a test where the dogs were suddenly presented with a small children's toy suspended from a ceiling, dogs of all ages reacted to the object stimulus with the same speed, but dogs of older age lost interest faster than younger dogs did.

In a second test, a person who was known to all the dogs came into the room to begin miming painting a wall with a paint roller. All the dogs watched the person pretending to paint longer than they had paid attention to the toy.

"So-called social attentiveness was more pronounced in all dogs than 'non-social' attentiveness." Wallis says. "The dogs generally tended to react by watching the person with the object for longer than an object on its own."

Dogs, like humans, also experience a difficult phase in adolescence (one to two years for dogs) during which they have difficulty paying attention, the researchers found.

During that period, dogs experience hormonal changes similar to what people undergo in puberty.

With age, dogs -- again like humans -- are less likely to react strongly to new experiences or objects in their environment, Wallis says.

"We found that older dogs -- like older human beings -- demonstrated a certain calmness. They were less affected by new items in the environment and thus showed less interest than younger dogs."

The finding that attentiveness levels change over a dog's life makes them an appropriate model to study some psychological, age-related human diseases like Alzheimer's or ADHD, the researchers said.