Such a consciousness-meter needs to be valid for subjects in the following five conditions
(1) neuro-typical adults in wake and different stages of sleep (REM sleep, deep sleep); (2) neuro-typical infants and children in wake and different stages of sleep; (3) neurological and psychiatric patients such as those in coma, vegetative-state, minimal conscious state, locked-in stage, late-state dementia, catatonia, delirium and dissociative states (some of which are and some of which are not conscious) (4) patients put “to sleep” using a range of anesthetic agents (enflurane, isoflurane, methoxyflurane, midazolam, propofol) (5) neuro-typical adults using hallucinogenic drugs (such as ketamine at low doses, LSD, psilocybin).
Such well-validated methods need to have been published, by two or more independent groups, in the peer-reviewed literature involving hundreds of subjects. The procedures must be validated on individual, clinically unambiguous cases, have a very low miss rate (labeling somebody unconscious when they are, indeed, conscious) and a low false alarm rate (labeling somebody conscious when they do not feel anything).
A reliable device that can detect, from the perspective of an external observer, whether a person is or is not consciousness – even when they are behaviorally impaired, is a major achievement in the two millennia-long debate concerning the mind-body problem. Brain science & technology is sufficiently advanced that this is becoming a real possibility now
Such a device could then be extended to other mammals such as primates or rodents, and to other species, including those with very different brain architectures, such as corvids, cephalopods and bees.
For references to the literature, see Koch C. (2017) How to make a Consciousness Meter. Scientific American November, 28-33.
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