Human behavior, in a physiologic sense, may be defined as visceral and muscular activity. If one starts with the premise that activity of the central nervous system is expressed by muscular movements, then direct observation of such phenomena should be an important and valid method for the study of normal as well as abnormal human behavior.
The investigation of muscular movements abounds with many difficulties and limitations. The various types of motor phenomena which come under this heading are so numerous and ambiguous as to kind and frequency that no two authors agree entirely in their designation. The definitions of these phenomena, referred to in medical and psychologic literature as tics, habit spasms, stereotyped acts or motor automatisms, vary with the school of thought. The most comprehensive definition was first propounded by Meige and Feindel in 1906:
A tic is a coordinated purposive act, provoked in the first instance by