The ability to reflect on one’s own cognitive processes, which psychologists call metacognition, was believed to be restricted to humans and other primates. But a study published in Current Biology now shows that rats are capable of assessing their own knowledge.
Jonathan Crystal and Allison Foote, of the University of Georgia’s Department of Psychology, taught rats to associate two different auditory stimuli with different levers. A short burst of static, lasting around 2 seconds, was associated with one lever, and a longer burst, lasting up to 8 seconds, with another. In the second phase of the trials, the sounds were played back to the rats. When the lever associated with each sound was correctly pressed, the rats were given a large reward – 6 food pellets. But if the wrong lever was pressed, they received no reward. The rats were also given the option to decline taking the test – they learnt that they could retrieve a smaller reward – 3 food pellets – without making a decision about which lever to press, by poking their snout through an aperture in a food trough.
During the test phase, the rats were presented with the short and long bursts of static, as well as with bursts of intermediate length, and their responses were recorded. When the length of the sound burst was unambiguous (i.e. either short or long) they ignored the food trough and pressed the lever associated with the sound, so that they received the large reward. But when sounds of an intermediate length (approximately 3 seconds) were played, the rats frequently declined to take the test, and chose instead to retrieve food pellets from the food trough, suggesting that the rats knew that they did not know how to respond in the duration discrimination test.
In these trials, the rats had a choice: if they knew the “answer”, they could press the correct lever and receive the reward, but if they didn’t know which lever to press when a sound was played back, they could choose to decline the test and instead opt to retrieve the smaller reward from the food trough. In order to determine that the rats were indeed avoiding the test because they didn’t know how to respond, Crystal and Foote devised another experimental procedure. The food trough was removed, so that the only option available to the rats was to press one of the levers. It was found that the wrong lever was pressed far more frequently than the right one in response to sounds of intermediate length. The more difficult it was for the rats to discriminate the length of the sound played back to them, the more frequently they pressed the wrong lever.
This study shows that the cognitive processes of rats are more similar to those of humans than we believed they were. It is one of a number of recent studies which show that animals are capable of cognitive processes once thought to be either restricted to primates or uniquely human. Last year, Plotnik et al showed that elephants are capable of self-awareness. Earlier this year, psychologists from the University of Cambridge showed that scrub-jays can plan for the future, and a group of anthropologists from the University of Iowa filmed chimps making spears and using them to stab bushbabies.
Foote, A. L. & Crystal, J. D. (2007). Metacognition in the rat. Curr. Biol. DOI: 10.1016/j.cub.2007.01.061 [Full text]