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Humans adapt their behavior not only by observing the consequences of their actions but also by internally monitoring their performance. This capacity, termed metacognitive sensitivity [1 ; 2], has traditionally been denied to young children because they have poor capacities in verbally reporting their own mental states [3; 4 ; 5]. Yet, these observations might reflect children’s limited capacities for explicit self-reports, rather than limitations in metacognition per se. Indeed, metacognitive sensitivity has been shown to reflect simple computational mechanisms [1; 6; 7 ; 8], and can be found in various non-verbal species [7; 8; 9 ; 10]. Thus, it might be that this faculty is present early in development, although it would be discernible through implicit behaviors and neural indices rather than explicit self-reports. Here, by relying on such non-verbal indices, we show that 12- and 18-month-old infants internally monitor the accuracy of their own decisions. At the behavioral level, infants showed increased persistence in their initial choice after making a correct as compared to an incorrect response, evidencing an appropriate evaluation of decision confidence. Moreover, infants were able to use decision confidence adaptively to either confirm their initial choice or change their mind. At the neural level, we found that a well-established electrophysiological signature of error monitoring in adults, the error-related negativity, is similarly elicited when infants make an incorrect choice. Hence, although explicit forms of metacognition mature later during childhood, infants already estimate decision confidence, monitor their errors, and use these metacognitive evaluations to regulate subsequent behavior.


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