PT121 · S1 · Q1 The effort involved in lying

This somewhat diminishes the conclusion. We could try to argue that lie-detector tests aren't going to be a perfect method because there are some reactions they can't measure. But that's a potentially irrelevant response. If there are things that always accompany lying (like a sped up heartbeat), and a lie-detector can measure those reactions reliably well, then the lie-detector would still theoretically work.

People's awareness or lack thereof of their physiological reactions doesn't have anything to do with our goal, unless the answer is telling us that their awareness of being tested gives way to false positives. i.e., if we heard that "the awareness of subjects that their physiological reactions are being measured often triggers physiological reactions that are similar to those when people lie", that would weaken. That would make it seem like the test would produce false positives, because honest people who are just nervous about being measured might trigger the test to think that they were actually lying. But this answer doesn't take us into that useful objection territory. It only mentions people being unaware that their physiological symptoms are being measured.

If we were told that "lies about crimes are easier to detect than are lies about other things", that would give us a way to say that lie-detectors are not a sure way of determining when someone is lying. We could argue that when you're lying about unimportant things, it's a fainter reaction and so the test might not detect our lie. But this answer is ruling out the objection that crime-lies produce much stronger reactions than other-lies. When we rule out an objection, we mildly strengthen.

This talks about people's incentive to lie, but we're only here to evaluate whether the test itself will be a reliable indicator of determining when someone is lying. This doesn't say anything that affects our judgment about how reliable the test will be.