Assessing metacognition skills in non-human animals is made difficult by our limited ability to communicate with animals about abstract information or concepts. But in past work, metacognition in primates had been successfully probed by employing an ingenious technique: Animals were familiarized with a test that assessed a certain kind of knowledge that they may or may not have obtained during a "study period," and were then given a choice of taking the test or declining it. Animals were taught that by electing to take the test and passing it, they would receive a large reward, but that failing the test would yield no reward. Declining the test would yield a small reward. Therefore, animals faced with the decision of taking or declining the test would, in principle, have the chance to weigh the likelihood that they would pass the test (and receive a large reward) against the option of declining the test and receiving a certain, but smaller, reward.
In the new work, researchers utilized this approach to study the knowledge rats had of the information they possessed. During the "study phase" of the experiments, rats were presented with a brief noise of either short duration (between 2 and 3.6 seconds in length) or long duration (between 4.4 and 8 seconds). In the subsequent test, rats had to classify the recent noise as either "short" or "long"—a relatively easy choice if the noise fell to one extreme or another (for example, 8 seconds), but a difficult choice if the n