The visual effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is "seeing black",[citation needed] an apparent sense of blindness. A flickering ganzfeld causes geometrical patterns and colors to appear, and this is the working principle for mind machines and the Dreamachine.[1] The ganzfeld effect can also elicit hallucinatory percepts in many people, in addition to an altered state of consciousness.