startle response
an unlearned, rapid, reflexlike response to sudden, unexpected, and intense stimuli (e.g., loud noises, flashing lights). This response includes behaviors that serve a protective function, such as closing the eyes, frowning by drawing the eyebrows together, compressing the lips, lowering the head, hunching the shoulders, and bending the trunk and knee. The reaction can be neutralized by context, inhibition, and habituation. Also called startle reaction.