[From Greek epiphenomenon: something that appears in addition, a secondary symptom.]
(metaphysics) The doctrine that consciousness is merely a secondary symptom of the underlying processes of the physical brain. An analogy is that consciousness is like a panel of multi-colored lights on a science-fiction computer: it's attractive, but it does not affect the operation of the machine. Unlike some radical forms of behaviorism, epiphenomenalism does not deny the subjective experience of consciousness, although it does deny that consciousness has causal efficacy.