Thoughts don't just flit around in our heads unobserved: humans know when something's going on in our own brains, and we evaluate our own thoughts. For example, we can judge when we're not certain about something, and act accordingly. This ability, called metacognition (thinking about thinking), has been found in a number of species, but humans are unusual in our ability to communicate what we know about our own thoughts and knowledge.

How early in life do we develop metacognition? Children under the age of four, who confidently proclaim knowledge of things they can’t possibly know, seem to be pretty bad at it. Babies, on the other hand, point at things to ask questions about them. They shouldn't be able to do this unless they've worked out that they don't know something.

It’s possible that previous experiments haven’t found evidence of metacognition in younger children because they just weren’t testing it in the right way. After all, other species have metacognition, and experimenters have found ways to test that even though the animals can’t talk about what they know. What if children under four-years-old experience and use metacognition but are just bad at realizing it and letting anyone know?

Researchers at a cognitive science lab at Paris Sciences et Lettres Research University investigated this question by setting up an experiment that tested babies’ metacognition without forcing them to talk about it. They found evidence that the babies looked to their parents for help when they didn't know the answer to something.

Here's how the researchers adapted an experiment that had previously been used with rhesus monkeys: show a toy to an infant before hiding it. After waiting 3 to 12 seconds for the baby's mind to wander, instruct the baby to point to where the toy is hidden in order to get it back.

The researchers did this with 80 infants, all between 19 and 21 months. Each baby did this four times as practice (what professionals call "training trials") then a further 10 times. Half of those times the babies saw where the toy was hidden—that is, they knew where it had gone—and half of the time they didn’t get to watch, meaning that they couldn’t know where the toy was.

Two different groups were set up. All the babies had a parent or other caregiver present, but for half of them (the control group) the parent was told to be unresponsive if the baby looked at them for help. During the training trials, the parents in the other group demonstrated that they knew where the toy was all the time and would help the baby find it—but only if the baby looked at them for help.

The researchers found that the babies who were able to ask for help performed with better accuracy than the control group, finding the toy 66 percent of the time compared to the control group’s 56 percent—a statistically significant result. Fourteen of the babies in the group with help never actually asked for it, and their performances suffered accordingly: they had a similar accuracy rate to the babies who weren’t able to ask for help. Among those who asked for help, they were more likely to ask after a longer delay, or when they had not seen where the toy was hidden.

The researchers also looked at how many right and wrong guesses each group made. They reasoned that if the babies were thinking about what they didn’t know, they should ask for help more when they were unsure of where the toy is. This means the toddlers should make fewer mistakes but not necessarily find the toy more often. This turned out to be the case. There were more incorrect guesses in the control group, but around the same number of correct guesses for both groups (the babies sometimes didn't respond, so the number of total responses wasn't identical for each baby).

A problem with this experiment is that the babies were actually taught that they could ask their parents for help. This eliminates the possibility of knowing whether they would do so spontaneously. So, this experiment doesn't really tell us whether babies would normally and naturally communicate their uncertainty without any suggestions.

However, this problem doesn't undermine the finding that when the babies were shown that help was an option, they knew when to ask for it. That result does suggest that they were able to track their own uncertainty. More experiments on metacognition in very young children could help researchers to establish why there's a difference between this result and the previous studies that showed toddlers fail dismally at metacognition tasks—whether it's true that babies really are good at thinking about thinking and just bad at talking about thinking about thinking.

An earlier version of this article stated that one of the findings was statistically insignificant. This error has been corrected.

PNAS, 2015. DOI: 10.1073/pnas.1515129113 (About DOIs).