A major diagnostic feature of autism is self-stimulation. Self-stimulation is identified as repetitive, stereotyped behavior with the sole purpose of stimulating one's own senses. Examples include rocking one's body, spinning oneself, inappropriate jumping and hand flapping. Other forms of self-stimulation can be manipulation of objects (twirling a string, rolling paper, etc.), visual tracking of objects or hand regarding. The production of vocal sounds like grunting, humming, yelling, and repeating phrases out of context is also considered a form of self-stimulation. Yet another form involves obsessions with rituals or routines, such as lining objects up and holding items. Many people with autism report that some forms of self-stimulation may serve a regulatory function for them (i.e., calming, shutting out an overwhelming sound, reducing stress in uncomfortable situations).