One thing that seems to set humans apart from all other animals is our ability to reason. When the barometer falls, for example, we expect bad weather, but we don't think the barometer causes the weather. Scientists have assumed that such an understanding is beyond other animals. But a study of the reasoning abilities of rats now shows that we may not be so unique after all.
Even young children have a deep understanding of cause and effect--they are not surprised when a toy train derails at a break in the tracks--but the rest of the animal world seems to be limited to learning by association. In a classic experiment by the Russian physiologist Ivan Pavlov, dogs learned to associate dinner with the sound of a bell. The dogs would salivate whenever a bell rang even if no dinner was around, indicating a simple association between events that happen closely in time.
The new experiment started out much the same way. First, the researchers trained rats to associate a tone with the appearance of sugar snack inside a small niche in the wall. Then, instead of just observing events, the rats were given an opportunity to cause them. A lever was introduced which, when pressed, sounded the tone. The question was: Would the rats expect food to follow the tone even though they had caused it? If they had learned by association, the rats should expect a treat.
But the rats did not look for food after causing the tone. This suggests that rats understand the difference between events they cause and those they merely observe, the team reports 17 February in Science. "When it rains, you expect that both your lawn and your neighbor's lawn will be wet," says Michael Waldmann, an experimental psychologist at the University of Göttingen, Germany, "but if you water your lawn, you wouldn't expect your neighbor's to also be wet. And this is the type of reasoning the rats are using." Waldmann co-led the work with Aaron Blaisdell, a behavioral neuroscientist at the University of California in Los Angeles, California.
The study is "very surprising," says Anthony Dickinson, an experimental psychologist at the University of Cambridge, U.K., because the mainstream view is that "causal reasoning is restricted to humans and possibly dependent upon language." The reason that such abilities have escaped detection is that researchers "have just never thought of [an experiment] as clever as this."