How would you tell the difference between a human-level AI and a human? Sentience is not a well defined term. The best thing you can do is to ask the intelligence in question whether has subjective experience, if it says yes you have to believe that. I couldn't prove to you that I have subjective experiences. I think it's irrational to say that every cognitive ability a human has can be simulated perfectly fine on a computer, but only a biological brain is capable of subjective experiences.