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How does the human startle reflex differ from the startle reflex of most other mammals?
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Avoidance behaviour
Cat fleeing by upward climbing.
In the context of avoidance behaviour, the startle reflex is a protective mechanism shared by humans and other mammals. While the reflex generally involves the closing of eyes, the checking of breathing, and the pulling back of mouth corners to expose teeth across many species, there is a distinct difference in limb movement:
- Most mammals: The limbs typically flex as if the animal is preparing to leap.1
- Humans: The arms are thrust outward, as if the individual is preparing to grasp at a support.1
This rapid, involuntary response is considered an instinctive mechanism for self-defense, occurring in all normal humans and mammals when tested under uniform conditions.2