The "Clever Hans Effect"
So how do we know the Clever Hans' effect isn’t at work with Rico? Rico was able to find a requested item in a room alone (with his owner out of sight), which convinced the researchers that the dog could not merely be picking up physical cues from his owner.
What Rico tells us about a dog's understanding of language
After being featured on a television show for his ability to understand 200 words, a border collie named Rico intrigued some researchers at the Max Planck institute. These researchers asked if they could bring Rico in to perform some experiments to find out just how far they could stretch the dog's language ability. The answer: surprisingly far.
At first, the researchers wanted to verify in a controlled setting whether Rico really knew 200 words. To do this, they collected 10 items with which Rico was familiar. At the verbal command of his owner, they had him fetch a specific item from a separate room. Rico performed very well at this task, but the researchers wanted to challenge him further. Next, they chose a new item -- one that Rico had never seen in his life -- and placed it in the room among the familiar items. The owner requested that new item by name and, lo and behold, Rico brought back the new item.
Researchers performed this test several times, each time with another new item, and found that Rico brought back the correct item an impressive 70 percent of the time. This demonstrated not only that the dog had a large vocabulary, but also that he knew how to use process of elimination.
Impressed as they were, researchers pushed Rico further with an even more difficult task. They wanted to find out whether Rico could remember the items that he learned in the experiment after only one exposure, a process called fast-mapping, which children can do. One month after Rico proved his language abilities in the lab, researchers brought him back in. This time, they put one of the new items that Rico correctly fetched a month earlier in a room with four familiar and four unfamiliar items. When his owner requested it, Rico was able to correctly fetch the item he had learned a month previous as much as 50 percent of the time. Though that might not seem remarkable, it was to the researchers, because this success rate compares with that of 3-year-old children.
However, whether a dog's "understanding" of a word compares to a child's is another matter. In order to address that question, we'll need to get a better grasp on how language works, and we'll do that on the next page.