Potential research participants are told enough about an upcoming study to enable them to choose whether or not to participate. This illustrates:
the practice of seeking a representative sample.
informed consent.
an operational definition.
a placebo effect.

During early infancy, babies are extremely egocentric. They have no concept that the world exists separate from their point of view and experience. To understand that objects continue to exist even when they are unseen, infants must first develop a mental representation of the object.

hope this helps. Have a great night:)