Altercentric Memory Error at 9 Months But Correct Object Memory by 18 Months Revealed in Infants' Pupil

It was recently proposed that infants have a memory bias for events witnessed together with others. This may allow infants to prioritize relevant information and to predict others' actions, despite limited processing capacities. However, when events occur in the absence of others, for example, an object changes location, this would create altercentric memory errors where infants misremember the object's location where others last saw it. Pupillometry presents a powerful tool to examine the temporal dynamics of such memory biases as they unfold. Here, we showed infants aged 9 (N = 97) and 18 months (N = 79) videos of an agent watching an object move to one of two hiding locations. The object then moved from location A to B, which the agent either missed (leading to her false belief) or witnessed (true belief). The object subsequently reappeared either at its actual or, surprisingly, its initial location. As predicted by the altercentric theory, 9-month-old infants expected the object where the agent falsely believed it to be and not where it really was, as indicated in their pupil dilation. In contrast, 18-month-old infants seemed to remember the object's actual location. Infants' memory errors did not predict correct action anticipation when the agent reached into one of the locations to retrieve the object. This indicates that infants show altercentric memory errors at a young age, which vanish in the second year of life. We suggest that this bias helps young infants to learn from others, but recedes as they become more capable of acting on the world themselves.