Final answer:
Habituation is a simple form of learning in which an animal stops responding to a stimulus after repeated exposure. Leslie's decreased startle response is an example of habituation.
Step-by-step explanation:
Habituation is a simple form of learning in which an animal stops responding to a stimulus after a period of repeated exposure. In this case, Leslie's startle response to loud noises has decreased over time because she has been exposed to the loud noise of a closing door multiple times. This is an example of habituation, which is a non-associative form of learning.