The startle response is a heightened arousal state where you are jumpy and easily startled by any sudden noises or movements. You can see this startle response when you have hypervigilance, which is a state where you are constantly scanning your environment for any signs of danger. It is this hyperawareness that makes you jumpy and easily startled, as you are constantly looking for any stimuli. Thus a sudden stimulus sets you off, and you are jumpy and your body prepares for fighting or fleeing. You can see this hypervigilance startle response in PTSD (post traumatic stress disorder).