jkaufman, the dimmer-switch metaphor of consciousness is intuitively appealing. But consider some of the most intense experiences that humans can undergo, e.g. orgasm, raw agony, or blind panic. Such intense experiences are characterised by a breakdown of any capacity for abstract rational thought or reflective self-awareness. Neuroscanning evidence, too, suggests that much of our higher brain function effectively shuts down during the experience of panic or orgasm. Contrast this intensity of feeling with the subtle and rarefied phenomenology involved in e.g. language production, solving mathematical equations, introspecting one's thoughts-episodes, etc - all those cognitive capacities that make mature members of our species distinctively human. For sure, this evidence is suggestive, not conclusive. But the supportive evidence converges with e.g. microelectrode studies using awake human subjects. Such studies suggest the limbic brain structures that generate our most intense experiences are evolutionarily very ancient. Also, the same genes, same neurotransmitter pathways and same responses to noxious stimuli are found in our fellow vertebrates. In view of how humans treat nonhumans, I think we ought to be worried that humans could be catastrophically mistaken about nonhuman animal sentience.