It's not as if the psychotricorder of "Wolf in the Fold" is ever exactly described as a lie detector, either. Rather, it is credited with the powers of giving the heroes a "detailed account" on what has happened to Scotty in the past twenty-four hours. Sounds like the device, if applied properly, would be able to recover and record Scotty's experiences and sensations somehow, playing back his memories. Hard to tell if that would help in determining whether those memories are truthful or not.
Timo Saloniemi
I actually was not referring to the psychotricorder. In the briefing room Scott puts his hand on a pad and the computer is able to tell without fail whether he is lying or not.
The "psycho-tricorder", BTW, is another device that is mentioned in only one episode of Trek . . . and it figures that it was Robert Bloch who came up with the concept. Get it? PSYCHO-tricorder??
Also, in "Journey to Babel," Mister Spock makes the comment about Thelev the "Andorian:" He has been subjected to questioning under Verifier Scan and truth drug; he reveals nothing." So evidently there is some kind "extract the truth" technology that they can and do employ.