Final answer:
Piaget would attribute the infant's reaction to their lack of object permanence.
Step-by-step explanation:
According to Piaget, the infant's reaction can be attributed to the fact that they lack object permanence. Object permanence is the understanding that even if something is out of sight, it still exists. In the scenario described, when the rattle is covered by the blanket, the infant looks away and picks up another nearby toy, indicating that they do not have the ability to remember or recognize that the rattle is still there.