I gave this some more thought, because I find this topic fascinating and important in light of recent developments in the field. Sentience requires the ability

I gave this some more thought, because I find this topic fascinating and important in light of recent developments in the field. Sentience requires the ability to perform computations and to store information. This is the most basic necessary precondition and rules out most inanimate objects from being sentient right away. The scenario of a patient incapable of any kind of perception (keep in mind that this includes touch, taste, smell, and pain) and incapable of conscious interaction (e.g. locked-in syndrome) can still be observably sentient (testable by monitoring brain patterns and various pain- and reflex tests). Pain response and cranial nerve reflexes in your example, would be considered signs of brain activity and sentience. They also qualify as perceiving and interacting with the environment, though passively. Their absence in many jurisdictions is equivalent to the death of the patient (specifically they are declared brain dead). This understanding of being alive or dead, however, is separate from our understanding of sentience. In the context of human being specifically, being alive is a requirement for being sentient. Generally, though, these are two different matters entirely. So back to your example: > I think I can imagine a patient who contacts a horrific virus that cuts off all external and bodily sensations. Locked-in syndrome comes to mind. > She is still fully cognizant but now feels herself to be bodiless, floating in nothingness. Speculation, but sure, why not. > From the outside, she seems to be asleep or paralyzed. She is kept alive by caretakers and her own autonomous processes but she can perceive none of it. Every coma patient can be described by that. > Is she sentient? Id say yes, but she nevertheless lacks some of the required conditions. The answer depends on what I outlined above. If she has pain response or cranial nerve reflexes, she's medically considered alive and if you want to also sentient. If the physical examinations return negative results, an EEG several days apart can be used as another indication. Flat-line EEGs some days apart are a good indicator of non-sentience due to lack of any activity thought to be required for sentience (i.e. the computation-part mentioned earlier). In addition, cerebral blood flow can be tested as well. The absence of intracranial blood flow would again indicate a complete lack of brain activity and therefore lack of sentience of any measurable kind. This of course is done over a period of time, not in an instant, as patients may still recover (though usually within days, not months or even years). So this adds another important part to the equation: time. So I need to clarify my previous proposal by including it: "Capable of perceiving and interacting with the environment at any point in its existence for a significant period of time." There. I think that's much better already, because it also excludes otherwise functional humans from being sentient (e.g. children born without a cerebrum, aka anencephaly) while including people who are temporarily (due to trauma or illness) incapable of perception or interaction.