How does the human nervous system maintain stability in a variable environment through the regulation of sensory input? William T. Powers, a physicist and cyberneticist, argues that behavior is not a response to external stimuli, but rather the process of controlling one's own perceptions. By applying control theory to biological systems, the author proposes a hierarchical model of human functioning that challenges traditional stimulus-response psychology.

Experts in cognitive science and cybernetics recognize this work as a foundational text for Perceptual Control Theory. Readers frequently note the technical density of the prose, which requires a firm grasp of systems theory to fully synthesize the author's arguments.