What is the earliest age that a rudimentary knowledge of object permanence has been found?

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Researchers have found that infants as young as 3.5 months old may have a rudimentary understanding of object permanence. This means that they may be able to realize that an object still exists even if it has been temporarily hidden from view. However, their understanding of object permanence becomes more developed as they grow older, with most infants fully grasping the concept by 8 or 9 months old.

What Is the Earliest Age That a Rudimentary Knowledge of Object