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WordNet
startle reaction

n. a complicated involuntary reaction to a sudden unexpected stimulus (especially a loud noise); involves flexion of most skeletal muscles and a variety of visceral reactions [syn: startle response]

Usage examples of "startle reaction".

Hippocampus significantly smaller, strong startle reaction, a tendency toward dissociation.

The ticcing had started up, the head jerk reminding me of the sort of startle reaction I sometimes experience when I'm on the verge of sleep.

I have read that there are two fears that cannot be trained out of us: the startle reaction upon hearing an unexpected noise, and vertigo.