Janine completed several tours of duty in Afghanistan. She suffers from PTSD. Now, back home in Texas, she is frightened by firecrackers and cars backfiring. The fact that these sounds scare her reflects a process of stimulus:

generalization

Explanation:

Stimulus generalization: In psychology, the term "stimulus generalization" is determined as one of the concepts associated with the conditioning theory. Stimulus generalization referred to as the propensity of a particular conditioned stimulus to give rise to a familiar response once a specific response had already been conditioned.

In the question above, the fact that these sounds scare Janine reflects a process of stimulus generalization.