The response to a sudden unexpected stimulus is conditioned not only by the nature of the stimulus itself, but also by the preceding general state of muscular tonus. When an individual is extremely relaxed a sudden loud stimulus causes little or no start and seems to lose its irritating character; while the same kind of stimulus, when an individual is in a state of muscular tenseness, will bring about a start and very considerable muscular contraction. (PsycINFO Database Record (c) 2006 APA, all rights reserved)