Answer:
Expectancy
Explanation:
Expectancy is the way people expect a certain thing to occurs.
Infants like Lucia still hasn't develop enough brain capacity to understand that individuals can move freely from one place to another. So, she most likely expected that her brother remain in the same place even after she stop paying attention to him.
When she looked back and she noticed her brother is gone and replaced by her mother, she would consider it something outside the realm of possibility. This would explain why she is amazed by the whole situation.
