> Is it that I'd have to account for the fact that they might irrationally believe in the machine, and adjust my performance to fit that irrational belief? We

> Is it that I'd have to account for the fact that they might irrationally believe in the machine, and adjust my performance to fit that irrational belief? Well, yeah, wouldn't you? I mean, the fact that you're being given a polygraph implies that your interrogator believes it has some effect that benefits them. And if you're completely convinced that that isn't true, meaning the human-with-polygraph is not more reliable than an unaided human, that still leaves the possibility that the human-with-polygraph is worse in a way that affects you. If there's a possibility for the device to convince your interrogator that you're being deceptive, but you're honest, you're taking a risk unless you attempt to avoid causing a false positive. Conversely, if there's a possibility for the device to convince your interrogator that you're being truthful, and you're deceitful, you're missing out on an advantage unless you attempt to cause a false negative. There's no case where your interrogator is better off, so your premise isn't invalidated; the polygraph itself is still bunk. But it's your interrogator's trust in it which has created a relative advantage for you if you play along. The exact same applies if they show up with a "psychic", although it might be harder -- or easier -- to manipulate.