When it comes to doggy intelligence, bigger may be better. Bigger dogs seem to outperform their smaller brethren in terms of short-term memory and self-control. Larger brain size is the likely reason, according to findings in people and other primates.

Nobody had thought to test this in dogs before now; but study author, Daniel Horschler, a University of Arizona doctoral student in Biological Anthropology, wanted to know.

Brain size did not seem to affect all types of intelligence, including the dogs' social intelligence and reasoning ability.

“Previous studies have been composed mostly or entirely of primates, so we weren't sure whether the result was an artifact of unique aspects of primate brain evolution,” said Horschler. “We think dogs are a really great test case for this because there's huge variation in brain size, to a degree you don't see in pretty much any other terrestrial mammals. You have Chihuahuas versus Great Danes and everything in between.”

The Chihuahuas didn't fare too well.

The study looked at data from over 7,000 purebred dogs from 74 different breeds. The data came from Dognition.com, a website that allows dog owners to test their dogs' mental/cognitive abilities by using a variety of game-based activities. Owners can, if they want, then submit their results to the site, where researchers can analyze them.

Short-term memory was tested by dog owners hiding a treat under one of two plastic cups while their dog watched. They then waited for up to two and a half minutes before permitting their dog to go after the treat. Smaller dogs had more difficulty remembering where the treat had been hidden.

To test self-control, owners placed a treat in front of their dog and then told their dog not to take it. When owners covered their eyes or turned away, larger dogs tended to wait longer before taking the forbidden treat than smaller dogs did.

No matter how they had been previously trained, larger breeds performed better on these two tests, presumably because of their larger brains.

While larger dogs outperformed smaller dogs on these tests that measure executive function — their mental control and self-regulation — brain size did not appear to affect all types of intelligence, including the dogs' social intelligence and reasoning ability.

In the future, Horschler is hoping to compare the cognitive abilities of specific breeds, such as the miniature poodle and the standard poodle, two breeds that essentially differ only in size.

The study appears in Animal Cognition.