“I believe that so much research has come out lately suggesting that we may have underestimated certain aspects of the mental ability of dogs that even the most hardened cynic has to think twice before rejecting the possibilities,” said Stanley Coren, a psychology professor at the University of British Columbia and an author of several books on dogs.

Dr. Coren’s work on intelligence, along with other research suggesting that the canine brain processes information something like the way people do, has drawn criticism. And there is good reason. For most of the last century the specter of a horse named Clever Hans hung over anyone who tried to prove that dogs were acting in thoughtful ways  not merely mimicking or manipulating people into believing that they in fact grasped human concepts.

Clever Hans was said to be able to count, make change and tell time by tapping his hoof, until investigators in the early 1900s learned that Hans was merely responding to his trainer’s body language, tapping when the trainer nodded his head. This provided an enduring example for those who believed thought was the exclusive domain of humans.

But in 2004, German researchers reported that a border collie named Rico could learn the name of an object in one try, had 200 objects in his repertoire and remembered them all a month later, all very human. Even skeptical animal behavior researchers found the Rico results impressive and sound. Is it possible that Rico turned the tide on the Clever Hans problem, even though there is debate about how we can reliably measure what dogs know?

By giving dogs language learning and other tests devised for infants and toddlers, Dr. Coren has come up with an intelligence ranking of 100 breeds, with border collies at No. 1. He says the most intelligent breeds (poodles, retrievers, Labradors and shepherds) can learn as many as 250 words, signs and signals, while the others can learn 165. The average dog is about as intellectually advanced as a 2- to 2-and-a-half-year-old child, he has concluded, with an ability to understand some abstract concepts. For example, the animal can get “the idea of being a dog” by differentiating photographs with dogs in them from photographs without dogs.

But Clive D. L. Wynne, an associate professor of psychology at the University of Florida who specializes in canine cognition and has himself said he met a border collie who knew 1,500 words, takes issue with efforts to compare human and canine brains.

He argues that it is dogs’ deep sensitivity to the humans around them, their obedience under rigorous training, and their desire to please that can explain most of these capabilities. They may be deft at reading human cues  and teachable  but that doesn’t mean they are thinking like people, he says. A dog’s entire world revolves around its primary owner, and it will respond to that person to get what it wants, usually food, treats or affection.

“I take the view that dogs have their own unique way of thinking,” Dr. Wynne said. “It’s a happy accident that doggie thinking and human thinking overlap enough that we can have these relationships with dogs, but we shouldn’t kid ourselves that dogs are viewing the world the way we do.”