in studying the scratch reflex, researchers have named a number of regions on the surface of the body as they relate to the reflex. a "pure form domain" is a region on the surface of the body, that when stimulated, elicits only one form of the scratch reflex. a "form" is a movement-related strategy used by the animal to perform the scratch; for example, to scratch the upper back, humans are limited to one scratch form, involving the elbow raised above the shoulder to provide access to the upper back. in addition to pure form domains, there also exist a number of "transition zones", which can be successfully targeted by more than one "form" of the reflex, and which usually lie at the boundary of two pure form domains.