It was Donald Rumsfeld who said something about known knowns, known unknowns, and unknown unknowns, and whilst that might have sounded like just more gibberish, he did have a point. Think back to the last time you sat an exam; perhaps you had a reasonable idea of whether or not you were going to do well in it. This is because you had an understanding of your knowledge on the subject that was to be tested and could make a prediction. This reflection about your mental processes is termed metacognition, and it has been identified in humans and other primates, but the trait was always thought to be the preserve of our extended family tree.

Now, new data published online in Current Biology shows that rats have this ability too. You're probably wondering how one would test for metacognition in a species that isn't too good with essay questions. The way it works is as follows: the animals are familiarized to a test that utilizes knowledge that they might have gained during a study period. The animals are then given the chance to accept or decline the test. If the test is accepted and passed, there is a large reward, and if it is declined there is a small reward. If the test is accepted but failed, then there is no reward at all.

In this study, Allison Foote and Jonathon Crystal at the University of Georgia tested rats' abilities to pass a duration-discrimination test where they heard either a short (2-3 sec) or long (4-8 sec) noise and then had to class the noise as either short or long by poking their noses into one of two holes. The study found that the harder the discrimination task was, the more often it would be declined by the rats, and that if they were not given the option to decline the test, their accuracy declined.

This is the first time that such behavior has been demonstrated in animals other than primates, and may well provide the opportunity to further study the molecular basis of metacognition, and also the evolution of different cognitive skills across the animal kingdom.