Metacognition in the rat

Abstract

The ability to reflect on one's own mental processes, termed metacognition, is a defining feature of human existence [1, 2]. Consequently, a fundamental question in comparative cognition is whether nonhuman animals have knowledge of their own cognitive states [3]. Recent evidence suggests that people and nonhuman primates [4-8] but not less "cognitively sophisticated" species [3, 9, 10] are capable of metacognition. Here, we demonstrate for the first time that rats are capable of metacognition--i.e., they know when they do not know the answer in a duration-discrimination test. Before taking the duration test, rats were given the opportunity to decline the test. On other trials, they were not given the option to decline the test. Accurate performance on the duration test yielded a large reward, whereas inaccurate performance resulted in no reward. Declining a test yielded a small but guaranteed reward. If rats possess knowledge regarding whether they know the answer to the test, they would be expected to decline most frequently on difficult tests and show lowest accuracy on difficult tests that cannot be declined [4]. Our data provide evidence for both predictions and suggest that a nonprimate has knowledge of its own cognitive state.

Figure 1. Schematic Representation of Experimental Design Showing Trial Sequence in Study, Choice, and Test Phases

After presenting a white noise (2–8 s; study phase), a choice phase provided an opportunity to take or decline a duration test; declining the test produced a guaranteed, but smaller, reward than was earned if the test was selected and answered correctly (test phase). To the extent that a rat is uncertain about how to classify the interval, it will (1) decline to take the test and (2) show lower accuracy when forced to take the test relative to trials on which it chose to take the test. Grey shading indicates an illuminated nose-poke (NP) aperture.

Figure 2. Rats Decline Difficult Tests and Show Degraded Accuracy When They Cannot Decline the Difficult Test

(A–D) Difficult tests (defined as stimulus duration near the subjective middle of the shortest and longest durations) were declined more frequently than easy tests (defined as stimulus durations near the shortest and longest durations). (E–H) The decline in accuracy as a function of stimulus difficulty was more pronounced when tests could not be declined (forced test) compared to tests that could have been declined (choice test). The x-axes are plotted in reversed order. Error bars represent SEM.