In this text, Mario Castillo describes the underpinnings of the term Perceptualism, a concept he developed for creating and perceiving paintings, which he has used to characterize his work since 1993. In terms of his creative process, Castillo explains that he draws on intellectual sources encompassing Postmodernism and Surrealism, as well as the lessons of the Yaqui Indian don Juan Matus (as told by the Peruvian-born American anthropologist Carlos Castaneda). In terms of his desired effect, Castillo says that he would like viewers’ optical experiences of his paintings to combine the spiritual aspect of gazing at mandalas with the optical vibrations of Op Art (that is, the shamanism of Don Juan Matus with the optics of Impressionism). Castillo ends by summarizing the process of experiencing his Perceptualist paintings in four steps: 1) the viewer is drawn into the painting, 2) the viewer focuses attention for at least thirty seconds, thereafter perceiving vibration on the picture’s surface, 3) the viewer affects the appearance of the painting by moving his or her body, and 4) after prolonged viewing, images begin to morph and “ . . . the viewer may begin to perceive a blackout, whiteout, or a field of active energy.” “By this final stage,” he concludes, “the viewer has experienced Perceptualism.”