Source: Skybrary

Definition

The startle response, which in professional circles is also referred to as amygdala (or limbic) hijack, is the physical and mental response to a sudden intense and unexpected stimulus. This physiological reaction, which is most commonly known as the “fight or flight” reflex, will occur in response to what may be perceived as a harmful event: an attack, a threat to survival, or more simply, to fear itself. The fight or flight response enables us to react with appropriate action: to run away, to fight, or sometimes, to freeze to be a less visible target. In some circumstances, it can also lead to actions inappropriate for the situation.

In aviation, startle effect can be defined as an uncontrollable, automatic reflex that is elicited by exposure to a sudden, intense event that violates a pilot’s expectations.[1]