Several studies on new-born and infant are based on the gaze, but depending on the age of the subject, the assumption is different. For new-born, a long gaze is supposed to mean that what they look at is agreeable. For infants, a long gaze is supposed to means that they are surprised.
On what are these two assumptions based? Can they be verified? If yes, at what age does the meaning of a long gaze change? And why does it change?