This is an automatic response established by training to an ordinarily neutral stimulus. Like Pavlov’s dogs salivating at the sound of bell which was conditioned to associate with food.
Sensitization: This refers to an increased reaction to many stimuli following exposure to one strong stimulus. It could lead certain stimuli becoming triggers over time due to repeated association with a traumatic event.
This is the tendency for the conditioned stimulus to evoke similar responses after the response has been conditioned. For example, if a car backfiring (which sounds like gunfire) triggers someone with PTSD, other loud noises might also become triggers.