Socrates is often quoted as having said, "I know that I know nothing." This ability to know what you know or don't know -- and how confident you are in what you think you know -- is called metacognition.

When asked a question, a human being can decline to answer if he knows that he does not know the answer. Although non-human animals cannot verbally declare any sort of metacognitive judgments, Jessica Cantlon, an assistant professor of brain and cognitive sciences at Rochester, and PhD candidate Stephen Ferrigno, have found that non-human primates exhibit a metacognitive process similar to humans. Their research on metacognition is part of a larger enterprise of figuring out whether non-human animals are "conscious" in the human sense.

In a paper published in Proceedings for the Royal Society B, they report that monkeys, like humans, base their metacognitive confidence level on fluency -- how easy something is to see, hear, or perceive. For example, humans are more confident that something is correct, trustworthy, or memorable -- even if this may not be the case -- if it is written in a larger font.

"Humans have a variety of these metacognitive illusions -- false beliefs about how they learn or remember best," Cantlon says.

Because other primate species exhibit metacognitive illusions like humans do, the researchers believe this cognitive ability could have an evolutionary basis. Cognitive abilities that have an evolutionary basis are likely to emerge early in development.

"Studying metacognition in non-human primates could give us a foothold for how to study metacognition in young children," Cantlon says. "Understanding the most basic and primitive forms of metacognition is important for predicting the circumstances that lead to good versus poor learning in human children."

Cantlon and Ferrigno determined that non-human primates exhibited metacognitive illusions after they observed primates completing a series of steps on a computer.

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The monkey touches a start screen.

He sees a picture, which is the sample. The goal is to remember that sample because he will be tested on this later. The monkey touches the sample to move to the next screen.

The next screen shows the sample picture among some distractors. The monkey must touch the image he has seen before.

Instead of getting a reward right away -- to eliminate decisions based purely on response-reward -- the monkey next sees a betting screen to communicate how certain he is that he's right. If he chooses a high bet and is correct, three tokens are added to a token bank. Once the token bank is full, the monkey gets a treat. If he gets the task incorrect and placed a high bet, he loses three tokens. If he placed a low bet, he gets one token regardless if he is right or wrong.

Researchers manipulated the fluency of the images, first making them easier to see by increasing the contrast (the black image), then making them less fluent by decreasing the contrast (the grey image).

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The monkeys were more likely to place a high bet, meaning they were more confident that they knew the answer, when the contrast of the images was increased.

"Fluency doesn't affect actual memory performance," Ferrigno says. "The monkeys are just as likely to get an answer right or wrong. But this does influence how confident they are in their response."

Since metacognition can be incorrect through metacognitive illusion, why then have humans retained this ability?

"Metacognition is a quick way of making a judgment about whether or not you know an answer," Ferrigno says. "We show that you can exploit and manipulate metacognition, but, in the real world, these cues are actually pretty good most of the time."

Take the game of Jeopardy, for example. People press the buzzer more quickly than they could possibly arrive at an answer. Higher fluency cues, such as shorter, more common, and easier-to-pronounce words, allow the mind to make snap judgments about whether or not it thinks it knows the answer, even though it's too quick for it to actually know.

Additionally, during a presentation, a person presented with large amounts of information can be fairly confident that the title of a lecture slide, written in a larger font, will be more important to remember than all the smaller text below.

"This is the same with the monkeys," Ferrigno says. "If they saw the sample picture well and it was easier for them to encode, they will be more confident in their answer and will bet high."