An agent's partial knowledge of a hidden array impacts infants' representations of object quantity.

Infants can represent the quantity of a set of hidden objects, but if the number of objects hidden in a location exceeds three, infants experience "catastrophic forgetting", failing to represent even a subset of the objects. Infants' representations of an object also are impacted by other agents' visual access to an object; infants represent what an agent observed about an object instead of what they themselves observed. Here, we asked whether an agent's partial visual access to a set of objects would impact infants' representations of the set's quantity, and if so, whether this impact would apply when infants' own representational limits are exceeded. Ten-14-month-olds (n = 85) completed an ordinal choice task in which they watched an experimenter distribute different quantities of crackers across two containers, and were allowed to crawl to one of the containers to obtain its contents. We manipulated whether the quantities hidden were within or outside of infants' capacity limits (1 vs. 2 or 1 vs. 4) and whether a second experimenter, who infants saw had also observed the crackers being distributed, had partial knowledge of the arrays (observing 1 vs. 1 or 1 vs. 2, respectively) or no knowledge. Infants' container choices suggested that they used the observing agent's perspective to represent quantity whenever she had partial knowledge of the arrays. Our results suggest that an agent's quantity representations may mandatorily supplant infants' own, and this may allow infants to represent a subset of objects in situations in which they would normally experience catastrophic representational failure.