Perceptual Control Theory (PCT), pioneered by the American systems scientist, physicist and psychologist W. Powis, advanced N. Wiener's control theory in the following three ways: (1) It combined control theory with theoretical biology, considered control mechanisms as the essence of life, and proposed a more complete model of control of life. (2) It developed the concept of purposiveness in control systems, created the scientific concept of baseline signal or baseline information, and established the purposive formulation of cybernetics. It transforms the ancient concept of purposivity into a concept of modern science and modern philosophy. (3) It proposes a multi-level control theory model and establishes a new discipline of cybernetic psychology, which is different from both behaviorist psychology and psychoanalysis. Because of this, the authors of this paper first provide a comprehensive introduction to this new theory. This theory is then applied to some extended studies of certain valueological, epistemological, and philosophical issues of technology.