USCO was an American art collective and commune that from 1963 to 1968 produced an array of immersive installations and nonlinear events aimed at heightening its audience’s consciousness and perception of surrounding reality, while exposing how this was becoming increasingly mediated. Quintessential figures of the 1960s psychedelic counterculture, the group’s vividly multicolored environments consisted in slide, film and light projections, kinetic sculptures, tie-dye fabrics, soundscapes, and stroboscopic devices that overloaded the human sensorium with audiovisual stimuli. The article explores USCO’s pioneering use of the sensitive media-based atmosphere as a medium with references to the theoretical discourses on the “medium” by Walter Benjamin and Marshall McLuhan. In order to contextualize USCO’s peculiar production, at the crossroads of art and technology, references will be made also to coeval art movements such as Pop Art, Happening and radical architecture, and practices such as “intermedia” and “expanded cinema.”